Bryant Thermostat Q674 Users Manual 60 2485 T874 Multistage Thermostats And Subbases

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T874 Multistage Thermostats
and Q674 Subbases
PRODUCT DATA

FEATURES
• T874 Thermostat has silent, dust-free mercury
switches operated by coiled bimetal elements.
• Heat anticipator(s) are adjustable or fixed cooling
anticipator(s) are fixed.
• Individual heat and cool levers and scales (most
models) for temperature setting located on top of
thermostat case.
• Cover thermometer on most T874 Multistage
Thermostat models.
• Locking cover and locking lever screws available for
T874 Multistage Thermostats.
• Versaguard™ Thermostat Guard or custom key lock
thermostat guards available for T874 Multistage
Thermostats.
• T874 Thermostat requires a Q674 Subbase.

APPLICATION
These thermostats and subbases provide low voltage control
of multistage heating and cooling systems, including heat
pump systems.

• Q674 Subbase provides system and fan switching,
wiring terminals and mounting base for T874
Multistage Thermostat.
• Adapter plate available for mounting Q674 on wall or
horizontal outlet box.
• Light-emitting diodes (LEDs) located on subbase for
easy reference.
• Up to three stages each of heating and cooling control
possible.
• Models with setpoint restrictions and locking cover
with no thermometer available for Department of
Defense (DoD) and other special applications.
• Outdoor reset used on some models to improve
thermal performance.

Contents
Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Understanding Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Cross Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

® U.S. Registered Trademark
Copyright © 2001 Honeywell • All Rights Reserved

60- 2485-8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SPECIFICATIONS

Tradeline Models

IMPORTANT
The specifications given in this publication do not
include normal manufacturing tolerances. Therefore,
this unit may not exactly match the listed specifications. This product is tested and calibrated under
closely controlled conditions, and some minor differences in performance can be expected if those conditions are changed.

T874 THERMOSTAT
• T874 TRADELINE models provide staged heat and/or cool
operation. See Table 1.
Table 1. Heating and Cooling Stages.
Models

A

B

C

D

E

F

Heating Stages

1

1

2

2

—

2

Cooling Stages

1

2

1

2

2

—

Super Tradeline®/Tradeline® Models

• T874A-F are standard models.

SUPER TRADELINE controls offer features not available on
TRADELINE or standard models, and are designed to replace
a wide range of Honeywell and competitive controls.

TRADELINE FEATURES:
• TRADELINE package with cross reference label and
special instruction sheet.
• T874A,C model available with factory stops for DoD
applications.
• T874A,C model available with adjustable temperature
locking stops.

TRADELINE models are selected and packaged to provide
ease of stocking, ease of handling, and maximum
replacement value. Specifications of SUPER TRADELINE
and TRADELINE controls are the same as those of standard
models except as noted below.

Super Tradeline Models
T874 THERMOSTAT
T874D Thermostat. Provides two stages of heating and two
stages of cooling. Use with Q674A-F Subbases.
Y594D (T874D/Q674E/TG504A) Thermostat/Subbase/key
lock cover package. Provides two stages of heating and
two stages of cooling. Includes a key lock cover for setpoint protection.
Y594G (T874G/Q674F) Thermostat/Subbase package for
heat pump. Provides two stages of heating and one stage
of cooling. Automatic changeover in heat or cool mode.
Available in beige or Premier White® color.
Y594R (T874R/Q674L) Thermostat/Subbase package for
heat pump. Provides two stages of heating and one stage
of cooling. Manual changeover in heat or cool mode. Available in beige or Premier White® color.
SUPER TRADELINE FEATURES:
• SUPER TRADELINE package with cross reference label
and special instruction sheet.
• SUPER TRADELINE model supplied with locking lever and
locking cover accessories.
• Includes adjustable temperature locking stops.
• T874D replaces T874A-F TRADELINE or standard models.

Q674 SUBBASE
Q674 switching subbases provide system and fan switching.
See Table 2.
Table 2. System and Fan Switching.
Q674

System

Fan

A

Heat-Auto-Cool

Auto-On

B

Heat-Off-Cool

Auto-On

C

Off-Auto

Auto-On

D

None

None

E

Off-Heat-Auto-Cool

Auto-On

F

Em. Ht.-Off-Heat-Auto-Cool

Auto-On

G

Off-Auto

None

J

Em. Ht.-Auto-Off

Auto-On

L

Em. Ht.-Heat-Off-Cool

Auto-On

TRADELINE FEATURE:
• TRADELINE package with cross reference label and
special instruction sheet.
• Q674A-E,G are standard (non-heat pump) models.
Q674F,J,L are heat pump models.

ORDERING INFORMATION
When purchasing replacement and modernization products from your TRADELINE® wholesaler or distributor, refer to the
TRADELINE® Catalog or price sheets for complete ordering number.
If you have additional questions, need further information, or would like to comment on our products or services, please write or
phone:
1. Your local Home and Building Control Sales Office (check white pages of your phone directory).
2. Home and Building Control Customer Relations
Honeywell, 1885 Douglas Drive North
Minneapolis, Minnesota 55422-4386 (800) 328-5111
In Canada—Honeywell Limited/Honeywell Limitée, 35 Dynamic Drive, Scarborough, Ontario M1V 4Z9.
International Sales and Service Offices in all principal cities of the world. Manufacturing in Australia, Canada, Finland, France,
Germany, Japan, Mexico, Netherlands, Spain, Taiwan, United Kingdom, U.S.A.
60-2485—8

2

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Standard Models

Thermometer Range: 42° to 88°F (6 to 31°C)

T874 THERMOSTATS

Changeover Differential: 4°F (2°C) minimum between heating and cooling (5°F [3°C] on T874W). Levers can be set
apart for greater separation.

Models: See Table 3.

Interstage Differential:
Standard Models: Mechanical differential is 1°F (0.6°C)
between heating or cooling stages; operating differential is
approximately 1.9°F (1°C) between stages in heating or
cooling.
Special Models: See Table 3.

Electrical Rating: 24 to 30 Vac.
Switching: Coiled bimetal elements operate mercury
switches.
Temperature Adjustment: Heating and cooling setting
levers, with separate scales located on top of thermostat
base. Common lever for heating and cooling on T874R;
one cooling lever on T874E,V; and one heating lever on
T874F,Q.

Finish: Beige or Premier White® finish.
Mounting Means: T874 Multistage Thermostat mounts on
Q674 Subbase. Subbase mounts horizontally on wall or
outlet box. Mounts on vertical outlet box with optional
193121A Adapter Plate Assembly.

Dimensions: See Fig. 1.
Temperature: Scale Range: 42° to 88°F (6° to 31°C) standard; optional ranges available.
THERMOSTAT MOUNTED
ON SUBBASE

SUBBASE
SIDE

FRONT
3/8 (10)
5-5/8 (143)

HEAT

50 60 70 80

3-9/32 (83)

50 60 70 80

COOL

1-1/2
(38)

50 60 70 80
3-7/16
(87)

3-1/2
(89)

FAN

AUTO

ON

FAN

OFF EM. HT. HEAT AUTO COOL

1-7/8 (48)

AUTO

ON

OFF EM. HT. HEAT AUTO COOL

5-1/8 (130)

2-3/16 (56)

M5849

Fig. 1. T874 Thermostat and Q674 Subbase dimensions in in. (mm).
Optional Specifications (T874 Only):
Temperature scale ranges are 40° to 75°F (4° to 24°C) heating and 75° to 90°F (24° to 32°C) cooling with stop; 44° to
68°F (7° to 20°C) heating, 80° to 86°F (27° to 30°C) cooling; 6° to 29°C (43° to 85°F) Celsius scale; 3° to 22°C (38°
to 72°F) and 26° to 32°C (78° to 90°F) cooling with stop.
Nonadjustable factory-added stop limits heating setpoint to
72°F (22°C) maximum and cooling setpoint to 78°F (26°C)
minimum.
OEM customer personalization.
Locking cover and locking lever (see Thermostat Accessories).
Thermostat cover without thermometer.
Adjustable locking temperature stops.
Voltage heat anticipation for first or second stage heat or both.
See Table 3.
Fast cycling on heating stage(s) for electric heat applications.
C815A Outdoor Thermistor for improved performance on
specified models.

Thermostat Accessories:
Locking Cover and Locking Lever Assembly: Part no.
194559R with thermometer; 194559S without thermometer. See Fig. 2. Includes cover, screws, and Allen wrench
for locking cover. The screws must be used to assure
proper operation.
Adjustable Lever Stop: Part no. 4074ECK; includes lever stop
and screws.
Universal Versaguard™ Thermostat Guard: Includes wallplate, ring base, guard cover, tumbler lock, two keys and
optional Honeywell logo insert. Double-wall construction
provides extra measure of tamper-resistance. Tamperresistant lock; key cannot be removed without being in
locked position. Vents in guard base allow airflow for optimum thermostat performance. See form 68-0104 for more
information.
—
TG511A1000: Clear cover.
—
TG511B1008: Opaque cover.
—
TG511D1004: Painted steel (off-white) cover. See
Fig. 2.

3

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Key Lock Cover: Part no. TG504A replaces existing T874
cover. Mounts on T874 base and covers thermostat settling levers and subbase switches. Includes LED window
and two keys. Should not be used with 193121A Adapter
Plate.

194559R Locking Cover
with Thermometer
Allen Wrench

—
—

TG504A1025: Blank face, internal thermometer.
TG504A1033: External thermometer. See Fig. 2.

TG511D1004 Includes
Painted Steel Cover,
Opaque Base and Wallplate

TG504A1033 Key Lock
Cover with External
Thermometer
Fig. 2. T874 Thermostat accessories.
Table 3. T874 Thermostat Specifications.

Anticipation
System Stages
Models and Options

Heating (Adj)

Replaces Applications Heat Cool Other Stage 1

Cooling (Fixed)

Stage 2 Stage 1 Stage 2

T874A—Standard and TRADELINE®.
— 72°F/78°F (22°C/26°C)setpoint
stops with locking cover.
— Adjustable anticipator set 0.4A.
— Adjustable locking temperature
stops (TRADELINE®).
— 72°F/78°F (22°C/26°C) setpoint
stops with locking cover, no
thermometer (for DoDa).

T872A

Standard

1

1

—

0.1-1.2A

—

0-1.5A

—

T874B—Standard and TRADELINE.

T872B

Standard

1

2

—

0.1-1.2A

—

0-1.2A

0-1.0A

T874C—Standard and TRADELINE.
— 72°F/78°F (22°C/26°C)set stops
with locking cover, no thermometer
(for DoDa).
— 12°F (7°C) differential between
H1 and H2 stages (T874C1125).

T872C

Standard

2

1

—

0.1-1.2A 0.1-1.2A

0-1.5A

—

0-1.2A

0-1.0A

0-1.2A

0-1.0A

—

—

0.120.6A

— Fast cycling.
T874D—Standard and SUPER
TRADELINE®.
— Adjustable locking temperature
stops (SUPER TRADELINE).

T872D

T874E—Standard and TRADELINE.
T874F—Standard and TRADELINE.
— Locking cover.
a
b
c
d
e
f
g

Standard

2

2

—

T872E

2-Stage Cool

T872F

2-Stage Heat

—

2

—

2

—

—

Department of Defense.
Changeover stage operates with heating.
Fixed voltage type anticipation.
Changeover stage operates with heating; a secondary changeover is provided in cooling switch.
Provides night setback used with standard T874 and timer-operated remote switching.
Manual changeover stage—use Q674B,L subbase.
Changeover stage operates with cooling.Q674 Subbases

60-2485—8

4

0.120.6A

0.1-1.2A 0.1-1.2A

—

—

0.1-1.2A 0.1-1.2A

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

— Fast cycling.
T874G—Heat pump, cool
changeover, with fast cycling.

Electric Heat
T872G

Heat Pump or
Standard

2

1

1b

0.120.6A

0.120.6A

0-1.0Ac

0.1-1.2A

— Fixed anticipator for H2.

0-1.0A

—

0.1-1.5A
0.120.6A

— Fast cycling.
T874H—Use with Q674C.

T872H

Heat Pump or
Standard

1

1

1b

0-1.0Ac

—

0-1.0A

—

T874J—Heat pump.

None

Heat Pump

2

1

2d

0-1.0Ae

0-1.5Ac

0-1.0Ac

—

T874K—Heat pump.

None

Heat Pump

2

1

1b

0.1-1.2A 0-1.5Ac

0-1.5A

—

T874L—Heat pump.

None

Heat Pump

2

1

—

0.1-1.2A 0.1-1.2A

0-1.5A

—

T874N—Heat pump, heat
changeover.

T872N

Heat Pump

2

1

b

0.1-1.2A 0.1-1.2A

0-1.0A

—

2

1

—

0.1-1.2A 0.1-1.2A

0-1.5A

—

e

—

0.1-1.2A

—

—

—

T874P—Heat pump.

1

None

Heat Pump

T874Q—Night setback heating.

T872Q

Standard

1

—

T874R—Heat pump.

T872R

Heat Pump

f

2

1

—

0-1.5Ac

0.1-1.2A

0-1.5A

—

T874S—Two-speed compressor heat
pump.

None

Heat Pump

2

2

1g

0-1.2Ac

0-1.2Ac

0-1.2A

0-1.0A

T874V—Standard.

None

Standard

—

1

—

—

—

0-1.5A

—

T872W

Heat Pump or
Standard

3

2

—

T874W—Heat pump and standard.
— Night setback heating.
a
b
c
d
e
f
g

0-1.2Ab 0-1.2Ac,d 0-1.2A

0-1.0A

Department of Defense.
Changeover stage operates with heating.
Fixed voltage type anticipation.
Changeover stage operates with heating; a secondary changeover is provided in cooling switch.
Provides night setback used with standard T874 and timer-operated remote switching.
Manual changeover stage—use Q674B,L subbase.
Changeover stage operates with cooling.Q674 Subbases

Mounting: Designed to mount horizontally on an outlet box
or the wall. Adapter plate assembly available for mounting
on a vertical outlet box (see Subbase Accessory).

Models:
See Table 4.
Electrical Ratings:
Switch Contacts: 2.5A at 30 Vac (7.5A inrush).
LED Lights (Optional): 30 Vac.

Finish: Dark brown or gray.

Switches: Two slide switches (one switch on Q674G and K;
no switches on Q674D) operated by levers. Switch position
is shown on scaleplate.

Dimensions in in. (mm): 3-1/2 (89)height; 5-5/8 (143) width;
5/16 (8) depth. See Fig. 1.

Table 4. Q674 Subbase Specifications.
Switch Positions
Models and Options

Replaces

Application

System

Fan

Use With

Q674A—Standard and TRADELINE®.
— Indicator LEDs.

Q672A

Standard

HEAT-AUTO-COOL

AUTO-ON

T874A-D

Q674B—Standard and TRADELINE.

Q672B

Standard

HEAT-OFF-COOL

AUTO-ON

— Provision for fan relay operation from

Heat Pump

external fan switch (isolate G terminal).

OVERRIDE-HEAT-

— Indicator LEDs.
Q674C—Standard and TRADELINE.

AUTO-ON

T874P

OFF-COOL
Q672C

— Indicator LEDs.

Standard

OFF-AUTO

AUTO-ON

T874A-H,W

Heat Pump

OVERRIDE-AUTO-

AUTO-ON

T874K,L,N

Standard

None

None

T874A-F

OFF
Q674D—Standard and TRADELINE.
— For use when subbase switching is not
required.

T874A-D
T874G,H,L,R

Q672D

5

T874P

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Q674E—Standard and TRADELINE.

Q672E

Standard

OFF-HEAT-AUTOCOOL

AUTO-ON

T874A-D

Q674F—Two LED models.
— EM.HT. light.

Q672F

Heat Pump

OFF-EM.HT.-HEATAUTO-COOL

AUTO-ON

T874C,D,G,N,S

OFF-COOL-AUTOHEAT-EM.HT.

AUTO-ON

— Provision for AUTO fan operation in
EM.HT.
Q674G—O and B terminals.

Q672G

Standard

OFF-AUTO

None

T874A-F

Q674J—Provision for AUTO fan operation

Q672J

Heat Pump

EM.HT.-AUTO-OFF

AUTO-ON

T874A,D,G,J

in EM.HT.
— Provision for outdoor thermistor.
Q674K—Standard.

Q672K

Q674L—Provision for AUTO fan operation in
EM.HT.

Q672L

Standard

Heat Pump

— Indicator LEDs.

EM.HT.-ON-OFF

AUTO-ON

SUPL.HT.-ON-OFF

AUTO-ON

OFF-HEAT-AUTOCOOL

None

OFF-WOOD-WOOD/
OIL-OIL

None

EM.HT.-HEAT-OFFCOOL

AUTO-ON

SUPL.HT.-HEATOFF-COOL

AUTO-ON

T874F

T874R,W

Q674N—Standard.

Q672N

Evaporative
Cooler

EVAP-COOL-OFFHEAT

AUTO-ON

T874C

Q674P—Standard.

Q672P

Heat Pump

SUPL.HT.-HEATCOOL

AUTO-ON

T874G

Q674Q—Standard.

None

Fan Coil

HEAT-OFF-COOL

LO-MED-HION

T874A

Q674R—Standard.
— International symbols.

None

Fan Coil

OFF-COOL

LO-HICONT.

T874V

Q674S—Indicator LED.

None

Standard

HEAT-COOL

None

T874C

Optional Specifications (Q674 Only):
Models available with up to four LEDs; for example, LEDs can
show EM. HT, AUX. HT, SERVICE, CHECK, FILTER, and
LOCKOUT. See Fig. 3.
System switching marked HEAT-OFF/RESET-COOL for systems requiring impedance relay reset. Available on Q674B
only.
G terminal isolated on heating to provide fan relay operation
from external low voltage fan switch (Q674B only).
Auto fan operation on both heat and cool.

T874 Thermostat with
One Setpoint Lever

L terminal is used for system monitoring devices.
Common R terminal for heating/cooling.
Changeover in cool or heat mode for heat pumps.
Auto fan in EM.HT. for heat pumps.
Subbase Accessory: 193121A Adapter Plate Assembly for
mounting on vertical outlet box. Assembly includes adapter
ring and cover plate. Use to cover wall marks from
replaced thermostat.

T874 Thermostat with
Separate
Heating and Cooling Levers
Fig. 3. Heating, cooling levers and system LED indicators.

60-2485—8

6

Q674 Subbase
with Four LEDs

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

— concealed pipes and chimneys.
— unheated (uncooled) areas such as an outside wall behind
the thermostat.

MERCURY NOTICE

This control contains mercury in a sealed tube. Do not
place control in the trash at the end of its useful life.
If this control is replacing a control that contains
mercury in a sealed tube, do not place your old control
in the trash.
Contact your local waste management authority for
instructions regarding recycling and the proper
disposal of this control, or of an old control containing
mercury in a sealed tube. If you have questions, call
the Honeywell Customer Response Center at
1-800-468-1502.

INSTALLATION
When Installing this Product…
1.
2.
3.
4.

Read these instructions carefully. Failure to follow them
could damage the product or cause a hazardous condition.
Check the ratings given on the product to make sure the
product is suitable for your application.
Installer must be a trained, experienced service technician.
After installation is complete, check out product operation as provided in these instructions.

Mount Subbase
The subbase can be mounted on a vertical outlet box,
horizontal outlet box or directly on the wall.
1. If the subbase is mounted on a vertical outlet box, order
Honeywell part no. 193121A Adapter Assembly. See
Fig. 4. The assembly includes an adapter ring, two
screws and a cover plate to cover marks on the wall.
Install the ring and cover plate on the vertical outlet box.
NOTE: For a wall installation, hold subbase in position and
mark holes for anchors. See Fig. 5. Wall anchors
must be obtained from local hardware store. Be
careful that the wires do not fall back into the wall
opening. Set aside subbase. Drill four
3/16 in. (4.8 mm) holes and gently tap anchors into
the holes until flush with the wall.
2.

Pull wires through the cover plate (if used) and subbase
cable opening. See Fig. 6.
3. Secure the cover plate (if used) and subbase with the
screws provided. Do not fully tighten the subbase
screws.
Level the subbase using a spirit level, see Fig. 7, and firmly
tighten subbase mounting screws. The subbase mounting
holes provide for minor out-of-level adjustments.
VERTICAL
OUTLET
1
BOX

MOUNTING
SCREWS (2)

CAUTION
Hazardous Voltage.
Can damage heating/cooling system.
1.
Disconnect power supply before beginning installation to prevent electrical shock or equipment
damage.
2.
Do not short across coil terminals on relay. This
can burn out thermostat heat anticipator.
3.
To prevent interference with the thermostat linkage, keep wire length to a minimum and run wires
as close as possible to the subbase.
4.
Do not overtighten thermostat captive mounting
screws because damage to subbase threads can
result.

COVER
PLATE 2

ADAPTER
RING 2

1
HORIZONTAL
OUTLET
BOX

THERMOSTAT

IMPORTANT
An incorrectly leveled thermostat will cause the temperature control to deviate from setpoint. It is not a
calibration problem.

CO

50

SUBBASE
HE

AT

50

60

70

60

70

THERMOSTAT
COVER

OL

80

80

SUBBASE
MOUNTING SCREWS (2)

Location
Install the thermostat about 5 ft (1.5m) above the floor in an
area with good air circulation at average temperature.

CAPTIVE
MOUNTING SCREWS (2)

Do not mount the thermostat where it can be affected by:
— drafts or dead spots behind doors, in corners or under
cabinets.
— hot or cold air from ducts.
— radiant heat from the sun, fireplace, or appliances.

1

NOT INCLUDED WITH UNIT.

2

ACCESSORY PART AVAILABLE (193121A).

50

60

70

80

M6009

Fig. 4. Installing Q674 Subbase on outlet box.

7

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

All wiring must comply with local electrical codes and
ordinances.
WALL

IMPORTANT
Use 18 gauge, solid-conductor wire whenever possible. If using 18 gauge stranded wire, no more than
10 wires can be used. Do not use larger than
18 gauge wire.

WIRES THROUGH
WALL OPENING

WALL
ANCHORS
(2)

M926

Follow equipment manufacturer wiring instructions when
available. To wire subbase, proceed as follows:
1. Connect the system wires to the subbase as shown in
the applicable diagram. A letter code is located near
each terminal for identification. Typical terminal designation and wiring connections are listed in Table 5. The
terminal barrier permits straight or wraparound wiring
connection. See Fig. 7. The subbase can require one or
more jumpers that may or may not be factory-supplied.
See Fig. 8 and the wiring diagrams for specific terminals
to be jumpered.

MOUNTING
HOLES

MOUNTING
SCREWS (2)

SUBBASE

Fig. 5. Installing Q674 Subbase on wall.

WIRING
TERMINAL

FOR STRAIGHT
INSERTION–
STRIP 5/16 IN. (8 MM)

THERMOSTAT
CABLE OPENING

FOR WRAPAROUND–
STRIP 7/16 IN. (11 MM)

SPIRIT LEVEL

BARRIER
SUBBASE TERMINAL SCREW

M928

Fig. 7. Barrier configuration.

CAUTION
POST FOR
MOUNTING
MOUNTING
HOLES (4)
THERMOSTAT (2)

Equipment Damage Hazard.
Never install more than one wire per terminal unless
using factory-supplied jumper with spade terminal.

TO SPRING FINGER
CONTACTS ON
THE THERMOSTAT
M927
(UP TO 12)

2.
3.

Fig. 6. Subbase components and leveling procedure.

4.

Wire Subbase
Disconnect power supply before beginning installation to
prevent electrical shock or equipment damage.

60-2485—8

8

Firmly tighten each terminal screw.
Fit wires as close as possible to the subbase. Push
excess wire back into the hole.
Plug hole with nonflammable insulation to prevent drafts
from affecting the thermostat.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

JUMPER WIRE
(SUPPLIED WITH SOME MODELS)

1

1
1 TWO ADJACENT TERMINALS SHOWN JUMPERED ARE FOR EXAMPLE ONLY. COMPARE WIRING
DIAGRAM AND SUBBASE TO IDENTIFY TERMINALS TO BE JUMPERED.
M5899

Fig. 8. Jumper adjacent terminals for special system hookup using stripped wire 3/4 in. (19 mm).
For nonadjacent terminals and using jumper wire supplied with subbase.
Table 5. Terminal Designationsa
Standard Terminal
Designation

Alternate Designations or
Customer Specials

E

K

Emergency heat relay

G

F

Fan relay coil

L

System monitor

O

R

Cooling damper motor; changeover valve

R

V

Power connection to transformer (internally connected for heating
and cooling)

RC

Power connection to cooling transformer

RH

Power connection to heating transformer

W1

H1, R3

Stage 1 heating control

W2

H2, Y, R4

Stage 2 heating control

W3

Stage 3 heating controlb

Y1

C1, M

Stage 1 cooling control

Y2

C2

Stage 2 cooling control
Stage 3 cooling control

Y3
X

X1,X2,C

T

A

Outdoor thermistor

L, C, H

HSII control panel

P
O
A, A1, A2, Z, C, L
a

b

Typical Connection
Heating damper motor; changeover valve

B

Clogged filter switch or common connection

Defrost
Momentary circuit, changeover
LEDs

Other terminal designations can be used that are not listed on this table. Refer to the hookup drawing and internal schematic
for exact connections.
W3 controls the auxiliary heat like W2, and allows adding additional stages of auxiliary heat with outdoor thermostats while
maintaining the proper second stage anticipation.

9

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 5. Terminal Designationsa
Standard Terminal
Designation

Alternate Designations or
Customer Specials

Typical Connection

T

External temperature readout, T relay

R1, R2
Y
a

b

LO and HI speed fan relays

RS

Cooling contactor

M

Compressor contactor

Other terminal designations can be used that are not listed on this table. Refer to the hookup drawing and internal schematic
for exact connections.
W3 controls the auxiliary heat like W2, and allows adding additional stages of auxiliary heat with outdoor thermostats while
maintaining the proper second stage anticipation.

Outdoor Disconnect
The National Electrical Code requires the installation of a
disconnect switch within sight of the outdoor unit of an air
conditioner or heat pump. The switch is for the safety of any
technician working on the unit. The technician can assure that
the unit remains unpowered.

Install and Adjust Stop Brackets
The stop brackets should be installed only if there is a need to
restrict the adjustable range of the heating and cooling
temperature setpoint levers. If adjustable lever stops are
desired, order 4074ECK Envelope Assembly, which contains
two adjustable lever stop brackets, one brass insert, one

mounting screw and two locking screws with insulated heads.
When installed, the stop brackets limit the movement of the
T874 HEAT and COOL levers.
TO INSTALL:
1. Remove the thermostat cover by pulling the bottom
edge of the cover upward until it snaps free of the
mounting slots.
2. Turn to the back of the T874 Thermostat. Locate the
hole for the brass insert in the plastic base below the
LED window.
3. Push the brass insert into the hole with finger.
4. Turn to the front of the T874 Thermostat.
5. Place the two stop brackets in position with the tabs in
the slot between the HEAT and COOL levers. See
Fig. 9.

HOLES FOR INSULATED
LOCKING LEVER SCREWS
COOL
LEVER
HEAT
LEVER

HOLE WITH
BRASS INSERT
BRACKET
TABS
ADJUSTABLE LOCKING LEVERS

ADJUSTABLE
LEVER STOP
BRACKETS

BRACKET
SLOTS

NONADJUSTABLE STOPS
WITH LOCKING LEVER SCREWS
75°F (24°C) MAX. HEAT
75°F (24°C) MIN. COOL

MOUNTING
SCREW

NONADJUSTABLE D.O.D. STOPS
72°F (22°C) MAX. HEAT
78°F (26°C) MIN. COOL

ADJUSTABLE STOPS

M7626

Fig. 9. Range limiting and lever locking methods.
6.

Insert the mounting screw into the two slots in the stop
brackets and attach to the brass insert. Tighten the
screw to pull the brass insert into the back of the ther-

60-2485—8

10

7.

mostat.
Loosen the mounting screw enough to free the stop
brackets for adjustment.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

8.
9.
10.
11.

Move the HEAT and COOL levers to the maximum temperature desired.
Slide the stop brackets until one rests against the HEAT
lever and the other against the COOL lever.
Firmly tighten the mounting screw.
If the HEAT and COOL levers are to be locked in place
at a specific temperature, use the two insulated head
screws supplied instead of the two adjustable lever stop
brackets.

ALLEN
RETAINING
SCREWS (2)

CAUTION
Equipment Damage Hazard.
Do not use standard screws that provide metal-tometal contact with the stop brackets. Short circuit and
potential equipment damage can result.
M956

Mount Thermostat
1.

Fig. 10. Installation of locking cover assembly.

Remove the thermostat cover by pulling the bottom
edge of the cover away from the base until it snaps free
of the cover clip.

SETTINGS

NOTE: The cover is hinged at the top and must be removed
by pulling up at the bottom.
2.
3.

4.

5.
6.
7.
8.

Carefully remove and discard the polystyrene packing
insert that protects the mercury switches during shipment.
If LED indication (EM.HT., CHECK, etc.) is to be used
with the Q674 Subbase, install the preprinted insert
under the thermostat setpoint scale. To install, push
both thermostat setpoint levers to the far ends of the
thermostat. Use index finger to gently pull out the plastic
setpoint scale about 1/4 in. (6 mm). Position the desired
preprinted insert in the space above the LED lights.
Reposition setpoint levers.
Turn over the thermostat base and note the spring fingers that engage the subbase contacts. Make sure the
spring fingers are not bent flat, preventing proper electrical contact with the subbase.
Set the heat anticipator indicator(s) to the respective
current setting of each stage. See Set The Heat Anticipator section.
If the thermostat provides optional locking cover assembly, start the Allen locking screws in the cover with the
wrench provided. See Fig. 10.
Note the two tabs along the top inside edge of the thermostat base. The tabs fit into corresponding slots on top
of the subbase. Mount the thermostat on the subbase.
Align the two captive mounting screws in the thermostat
base with the posts on the subbase. Tighten both
screws. Do not overtighten screws or damage to subbase posts can result.

CAUTION
Equipment Damage Hazard.
On systems using a gas valve, never apply a jumper
across the valve coil terminals, even temporarily. This
can burn out thermostat heat anticipator(s).

Set the Heat Anticipator
Move the indicator to match the primary control current draw.
When using a T874 Thermostat with two stages of heating,
set each heat anticipator to match its respective primary
control current draw. If you cannot find the current rating on
the primary control, or if further adjustment is necessary, see
NOTE and use the following procedure to determine the
current draw of each stage.
The current draw of each heating stage must be measured
with the thermostat removed and power on to the heating
system.
1.

2.
3.

Connect an ac ammeter of appropriate range between
the heating terminals of the subbase:
a. Stage 1—between W1 and RH or R;
b. Stage 2—between W2 and RH or R
c. Stage 3—between W3 and RH or R.
Move the system switch to HEAT or AUTO.
After one minute, read the ammeter and record the
reading:
a. Stage 1—__________A;
b. Stage 2—__________A;
c. Stage 3—__________A.

NOTE: If equipment cycles too fast, set the indicator to a
higher current rating, but not more than one-half division at a time, and recheck the cycle rate. Most conventional two-stage heating equipment is designed
to operate at three cycles per hour per stage, and
one-stage heating equipment at six cycles per hour,
at 50 percent load conditions. When using the T874
Thermostat in heat pump systems, set the heat

11

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

anticipator at 140 percent of the actual primary control current draw to reduce the cycling rate. See Fig.
11.
Most heat pump systems should cycle 2-1/2 to 3 times per hour.
Hang the upper edge of the thermostat cover on top of
the thermostat base and swing the cover downward
until it engages with the cover clip.

STAGE ONE
ANTICIPATOR
HEATING
CONTROL

.1

2.

10

1.2

.8.6

.5 .4

.3

.2

.15

.12

4.

.1

5

.2
.3
1.2 .8 .6 .4

STAGE TWO
ANTICIPATOR
HEATING CONTROL

MOVE INDICATOR TO
MATCH CURRENT RATING
OF PRIMARY CONTROL

M5069

Fig. 11. Adjustable heat anticipator scales.

Temperature Setting
Move the heating and cooling levers to the desired comfort
positions. See Fig. 12. On some models with two stages of
heating or cooling, the same lever controls both stages. The
minimum differential between heating and cooling setpoints is
4°F (2°C) (5°F [3°C]) on T874W.
If model has optional screws to lock temperature control
levers, loosen these screws before making temperature
adjustment; tighten the screws when levers are set at desired
position.
STAGE 1
HEATING
STAGE 3
HEATING

The subbase switching positions control the system operation
as described below.
SYSTEM SWITCH (see subbase for positions):
OFF—both the heating and cooling systems are off. If the
fan switch is at the AUTO position, the cooling fan is
also off.
HEAT—heating system is automatically controlled by the
thermostat. Cooling system is off.
AUTO—thermostat automatically changes between heating and cooling system operation, depending on the
indoor temperature.
COOL—cooling system is automatically controlled by the
thermostat. Heating system is off.
EM.HT.—emergency heat relay is automatically controlled
by the thermostat. Cooling system is off. Compressor is
de-energized.
SUPL.HT.—supplemental heat relay is energized. Cooling
system is off. Compressor is de-energized.
WOOD—heating system is operating with only the woodburning stage.
OIL—heating system is operating with only the oil-burning
stage.
WOOD/OIL—wood and oil stages operate sequentially;
first the WOOD stage operates, then the OIL stage
operates if the WOOD stage cannot handle the load.
EVAP—controls cooling system by water evaporation; see
equipment instructions for further information.
OVERRIDE—night setback is disabled.
ON—heating system is controlled by the thermostat. EM.
HT. or SUPL. HT. relay is not energized.
FAN SWITCH positions control fan operation as follows:
ON or CONT.—fan operates continuously.
AUTO—fan operates as controlled by the thermostat in
heat pump systems or conventional cooling mode; fan
operates as controlled by the plenum switch in conventional heating mode.
LO—fan operates constantly at low speed.
MED—fan operates constantly at medium speed.
HI—fan operates constantly at high speed.
To move the subbase switches to the desired control
positions, use thumb and index finger to slide the lever. The
lever must stop over desired function indicator position for
proper circuit operation.

HEATING
LEVER
COOLING
LEVER

Subbase Setting

STAGE 1
COOLING

Spring return momentary position switching feature is
available on selected subbase models. On these models, the
fan switch is positioned to the right of the system switch. By
moving the fan switch to the far right and releasing it, the ON
position circuit makes. The lever springs back on release. This
position is not marked on the subbase.

Setting the Adjustable Differential
STAGE 2
HEATING

STAGE 2
COOLING

CAPTIVE
MOUNTING
SCREWS (2)

The adjustable interstage differential feature, on a selected
T874D model only, can be identified by the scale and tension
screw near the heating and cooling mercury switches. See
Fig. 13. On this model, the number of degrees between the
making of the first and second stage mercury bulbs is
adjustable. This feature is especially useful if the first stage
controls the comfort temperature, and the second stage
controls the energy savings temperature. Timers, such as the
S6005, for insertion between the first and second stage
control points must be ordered separately.

M7625

Fig. 12. Internal view of T874W (three stages of
heating, two stages of cooling).

60-2485—8

12

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Each mark on the scale represents 1°F (0.6°C) The
differential is factory set at 2°F (1°C) the differential can be set
as high as 12°F (7°C) To set the adjustable interstage
differential, loosen the tension screw. See Fig. 13. Slide the
adjustable scale to align with the number of degrees desired
between stages. Use the lower edge of the tension screw
bracket as a guide for alignment. In heating, slide the lever
wider apart for a larger differential, or closer together for a
smaller differential. In cooling, slide the lever closer together
for a larger differential, or wider apart for a smaller differential.
While supporting the scale with hand, tighten the tension screw.

IMPORTANT
Support the scale with hand while tightening tension
screw. See Fig. 13. Failure to do so can result in
twisting and damaging bimetal coil.
HEATING SETPOINT LEVER
TENSION
SCREW

HEAT

CAUTION
Equipment Damage Hazard.
When the thermostat is used to control a two-stage
heating or cooling system, the second stage mercury
bulb must never make before the first stage bulb, or
severe equipment damage could result. To prevent
this problem, provide at least 2°F (1°C) differential
between stage-one and stage-two make points.
Example: in heating, if stage-one makes at 70°F (21°C)
stage-two should make at 68°F (20°C) or lower.

Verify the Adjustment
Heating
Start with the heating setpoint lever all the way to the left.
Slowly move the lever to the right, just until the first stage bulb
makes (mercury rolls to the right side of the bulb). Note the
setting on the temperature scale. Slowly move the lever to the
right until the second stage bulb makes. Note the setting on
the temperature scale. The difference between the two
temperatures is the interstage differential, which should match
the number set on the scale with the tension screw.

50 60 70 80
FIRST
STAGE
SWITCH

Cooling

.2

1.5

Start with the cooling setpoint lever all the way to the right.
Slowly move the lever to the left, just until the first stage bulb
makes (mercury rolls to the left side of the bulb). Note the
setting on the temperature scale. Slowly move the lever to the
left until the second stage bulb makes. Note the setting on the
temperature scale. The difference between the two
temperatures is the interstage differential, which should match
the number set on the scale with the tension screw.

1.2 .8 .6 .4

SCALE

.3

SECOND STAGE
(ADJUSTABLE)
SWITCH

HEATING

CHECKOUT

TENSION
SCREW
ALIGN LOWER
EDGE WITH
SCALE
NOTCH
10°F
SCALE

Heating

SLIDE LEVER
WIDER APART
FOR LARGER
DIFFERENTIAL

Move the system switch on the Q674 Subbase to HEAT or
AUTO. Move the heat lever on the T874 about 10°F (6°C)
above room temperature. See Fig. 12. Heating system should
start and the fan should run after a short delay. Move the heat
lever about 10°F (6°C) below room temperature. The heating
equipment should shut off, and the fan should run for a short
time, then shut off.

1

COOLING

In heat pump applications, sometimes time delays are
involved before the compressor and auxiliary heat are
activated. This is due to a minimum-off timer, which prevents
the compressor from restarting for five minutes from when the
thermostat last turned off the compressor, or from when the
system first received power.

TENSION
SCREW
ALIGN LOWER
EDGE WITH
SCALE
NOTCH
4°F
SCALE

SLIDE LEVER
CLOSER TOGETHER
FOR LARGER
DIFFERENTIAL

Cooling

1

CAUTION

1 EACH MARK ON THE SCALE REPRESENTS 1°F (0.6°C).

Equipment Damage Hazard.
Do not operate cooling if outdoor temperature is below
50°F (10°C). Refer to manufacturer recommendations.

M937

Fig. 13. Set adjustable interstage differential.

13

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Thermometer

Move the system switch on the Q674 Subbase to COOL or
AUTO. Move the cool setting lever on the T874 Multistage
Thermostat about 10°F (6°C) below room temperature. See
Fig. 12. The cooling equipment and fan should start. If the
system has two stages of cooling, both stages should start.
Move the cool lever about 10°F (6°C) above room
temperature. The cooling equipment and fan should stop.

The thermometer in your thermostat has been accurately
calibrated at the factory. The thermometer should only need
adjustment if it has been dropped or shifted due to mishandling.

Fan
Move the system switch to COOL, OFF, or AUTO. If
necessary, position both temperature setting levers so that the
heating and cooling equipment are off. Move the fan switch to
ON or CONT. The fan should run continuously. When the fan
switch is in AUTO, LO, MED, or HI position, fan operation is
controlled by the heating or cooling system.

Outdoor Reset Thermistor (Where
Applicable)
If the system is supplied with a thermistor, it must be used; if
not used, thermostat performance deviates radically from
proper operation.

If the setpoint lever and the thermometer reading do not
agree, use the following procedure:
1. Remove the thermostat cover by pulling up from the
bottom edge of the cover away from the base until it
snaps free of the cover clip.
2. Set the thermostat cover on a table near an accurate
thermometer.
3. Allow ten minutes for cover thermometer to sense area
temperature; compare the readings. Be careful not to
touch thermometer or breathe on it.
4. If the readings are the same, replace cover and put the
system into operation.
5. If the readings are different, insert a small screwdriver in
the thermometer slot and turn it until the thermometers
have the same reading. See Fig. 15.
6. Replace thermostat cover and put the system into operation.

THERMISTOR RESISTANCE (ohms)

The proper thermistor operation must be verified to ensure the
correct operation of the thermostat. Check thermistor
operations as follows:
1. Disconnect the T wire on the subbase.
2. Use an ohmmeter to measure resistance between the
T wire and the A subbase terminal.
3. Take outdoor temperature at thermistor location and find
the correct thermistor resistance on the Fig. 14 chart.
4. If the resistance measured in step 2 and the calculated
resistance in step 3 vary by more than 15 percent, the
thermistor requires replacement. Contact Honeywell or
installing dealer for replacement packaged outdoor thermistor, part no. C815A1005.
4600
4400
4200
4000
3800
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0

C815A THERMISTOR RESISTANCE
R = 400 ohms ± 10% AT 77°F (25°C)
M5070

Fig. 15. Thermometer calibration.

UNDERSTANDING CIRCUITS
To understand wiring diagrams, it is important to know what all
the symbols mean and how to trace the path of the circuits
from the transformer. See Fig. 16 through 25.
-20

0

20

40

60

80

100

120

TEMPERATURE OF THERMISTOR (°F)

Circuit descriptions and terminology are defined as follows:
For standard heating-cooling circuits:
Auto changeover—refers to the presence of an AUTO
position in the system switching (EX: Q674E with OFFHEAT-AUTO-COOL switching). The thermostat automatically changes between heat and cool modes as
indoor temperature changes.
Manual changeover—requires a system switch movement
to change mode (EX: Q674B with HEAT-OFF-COOL
switching). T874D Multistage Thermostats with 2 heat
or 2 cool switches are shown on most standard circuits.
Most standard or TRADELINE® subbases (Q674A-E,G)
can be used with T874A-F standard or TRADELINE

140

M1590A

Fig. 14. Thermistor resistance chart.

CALIBRATION
Thermostat
T874 Thermostats are accurately calibrated at the factory.
They do not have provision for field calibration.

60-2485—8

14

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

thermostats. The schematics can be field-modified as
required (EX: if T874C is being used, eliminate second
stage of heat).
For heat pump circuits:
Cool changeover valve—operates on cooling. The reversing valve or relay is activated either by moving the system switch to COOL (manual changeover) or by a
mercury switch that makes on a temperature rise (auto
changeover).
Heat changeover valve—operates on heating. The reversing valve or relay is activated either by moving the system switch to HEAT (manual changeover) or by a
mercury switch that makes on a temperature fall (auto
changeover).
System monitor relay—optional equipment on some heat
pumps includes an R4222P1065 or equivalent. This
system monitor relay detects a malfunction in the compressor and indicates the malfunction by activating the
EMERGENCY HEAT LED on the Q674 Switching Subbase. The system monitor relay is usually wired into the
L terminal on the Q674.
Each mercury switch is identified by function:
H1—Stage 1 Heating.
H2—Stage 2 Heating.
H3—Stage 3 Heating.
C1—Stage 1 Cooling.
C2—Stage 2 Cooling.
C3—Stage 3 Cooling.
C/O—Changeover (heat pumps).

5.

perature rise. Fixed anticipation is represented by a zigzag line and adjustable anticipation is a zigzag with an
arrow. The resistance of the fixed anticipator is so large
it limits current so that a system relay cannot be pulled
in from a circuit path going through the fixed anticipator.
The relay can be pulled in through an adjustable anticipator because its resistance is generally 0 to 5 ohms.
The center portion (the subbase) contains the switches.
The fan switch is above the system switch. The small
circles on the switch represent the maximum possible
contacts available on the Q674 Subbase. The larger circles represent the switch positions available on this particular Q674, with the solid circle representing where it
is actually switched on the diagram.

NOTE: Solid circles are not interconnected electrically.
At the right, the relays and contactors are shown, attached to
the proper terminals. The terminals are represented by large
circles with terminal designations in capital letters. See Table
3 for the meaning of each lettered terminal.
Sometimes power for a fixed anticipator is brought through an
off system relay like the changeover relay shown in Fig. 20.
This current is kept low by the high resistance of the fixed
anticipator so that relay does not pull in.

KEY TO HOOKUP SYMBOLS

Each anticipator is identified and each switch affected is
named (EX: H1 anticipator, C1 anticipator).
All T874 Multistage Thermostats use mercury switches. Each
schematic indicates switch operation by being drawn in the
open position with an arrow indicating operation with a
temperature RISE or FALL.

TRANSFORMER
(24 VAC SECONDARY)

RELAY/CONTACTOR CONTACTS
B
TERMINAL

RELAY OR CONTACTOR COIL

One circuit has been selected that is typical of various models
used with heat pumps. This circuit has been traced to
illustrate the functions performed by these control systems.

LED

MERCURY SWITCH

Tracing Method:
1.

2.
3.
4.

ODT
OUTDOOR THERMOSTAT
EHR
EMERGENCY HEAT RELAY

Always begin at the system transformer or R terminal.
You may want to draw the switch contacts in each
switch position to aid in tracing. Colored pencils are
helpful when only one copy of the circuit is available.
See Fig. 16 for a description of the hookup symbols and
Fig. 17 through 25 for typical hookups.
Completely trace only one circuit at a time (for example:
heat or cool).
Connections are indicated by small dots at the point of
intersection. If there is no dot, there is no connection.
The left portion of the circuit (the thermostat) contains
the mercury switches. The heat switches make on a
temperature fall, and the cool switches make on a tem-

15

FIXED ANTICIPATOR
HIGH RESISTANCE
(TYPICALLY 5 KILOHMS)

RTD
TIME DELAY RELAY
RD
DEFROST RELAY

ADJUSTABLE ANTICIPATOR
LOW RESISTANCE
(TYPICALLY 0 TO 5 OHMS)

CHP
PRESSURE SWITCH
LACO
LOW AMBIENT CUTOFF
M5848

Fig. 16. Key to hookup symbols.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
(HOT) L1

L2
1

H1/C1
ANTICIPATOR
R

2

FALL

ODT 1

H1

RTD 1

C1

EHR 1

RTD 2

W3
3

4

FAN SWITCH

ODT 2

AUTO
EHR 2

ON

H2
ANTICIPATOR

W2

5

H2

RTD 3

RTD 1

AUX. HT.
LED
(GREEN)

6

2

FALL

X
EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O

HEAT
OFF

COOL CHANGEOVER
VALVE

E

COOL

EM. HT.
RELAY

CHP

LACO
Y
B

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

AUXILIARY HEAT LED AVAILABLE ON SOME MODELS.

COMPRESSOR
CONTACTOR

M5072A

Fig. 17. Internal schematic and typical hookup of a T874R Thermostat and Q674L Subbase in a heat pump application.
The thermostat provides two-stage heating and one-stage cooling manual changeover operates on cooling.

60-2485—8

16

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

L1
(HOT)

R

H1/C1
ANTICIPATOR
FALL

SYSTEM COMPONENTS

ODT 1

L2

2

1
RTD 1

FAN SWITCH

H1
C1

EHR 1

RTD 2

W3
3
AUTO
4

ODT 2

ON
EHR 2

W2

H2
ANTICIPATOR
5
6

X
EM. HT.
LED (RED)

H2
FALL

SYSTEM
SWITCH

RTD 3

RTD 1

AUX. HT.
LED
(GREEN)

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O

HEAT
OFF

EM. HT.
RELAY

CHANGEOVER
VALVE

E

COOL
1

CHP

LACO

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

Y
COMPRESSOR
CONTACTOR

B

M5840

Fig. 18. Tracing the changeover relay circuit.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

H1/ C1
ANTICIPATOR
FALL

L1
(HOT)

R
ODT 1

2
RTD 1

H1

FAN SWITCH
C1

EHR 1

AUTO

ODT 2

ON

AUX. HT.
LED
(GREEN)

5

FALL

EHR 2

W2

H2
ANTICIPATOR

H2

X

6

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD
FAN RELAY

G

EM. HT.

O

HEAT
OFF
POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

RTD 3

RTD 1

L

1

RTD 2

W3

3

4

L2
1

CHANGEOVER
VALVE

E

COOL

EM. HT.
RELAY

CHP

LACO
Y
B

COMPRESSOR
CONTACTOR

M5841

Fig. 19. Tracing the heat 1 and anticipation circuit.

17

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

H1/ C1
ANTICIPATOR
FALL

L1
(HOT)

R

2

ODT 1
L2
1

H1

C1
3

RTD 1

FAN SWITCH

EHR 1

RTD 2

W3
4

AUTO

ODT 2

ON

H2
ANTICIPATOR

AUX. HT.
LED
(GREEN)

6

H2

EHR 2

W2

5

RTD 3

RTD 1

X

FALL

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O
HEAT
OFF
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

EM. HT.
RELAY

CHANGEOVER
VALVE

E

COOL
CHP

LACO
Y
COMPRESSOR
CONTACTOR

B

M5842

Fig. 20. Tracing the heat 1 anticipation circuit.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

H1/C1
ANTICIPATOR

L1
(HOT)

R
ODT 1

RTD 1
H1

L2

2

FALL

FAN SWITCH

C1

EHR 1

1

RTD 2

W3

3
AUTO
4

ODT 2

ON

AUX. HT.
LED
(GREEN)

5

H2

EHR 2

W2

H2
ANTICIPATOR

X

6

FALL

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O
HEAT
OFF
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

CHANGEOVER
VALVE

E

EM. HT.
RELAY

COOL
CHP

LACO
Y
B

COMPRESSOR
CONTACTOR

Fig. 21. Tracing the heat 2, anticipation and AUX. HT. LED circuit.

60-2485—8

RTD 3

RTD 1

18

M5843

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)

R

H1/C1
ANTICIPATOR

ODT 1
1
RTD 1

FAN SWITCH

H1

L2

2

FALL

C1

EHR 1

RTD 2

W3

3
AUTO
4

ODT 2

ON

AUX. HT.
LED
(GREEN)

5

FALL

RTD 3

RTD 1

X

6

H2

EHR 2

W2

H2
ANTICIPATOR

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O
HEAT
OFF
1

EM. HT.
RELAY

CHANGEOVER
VALVE

E

COOL
POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

CHP

LACO
Y
COMPRESSOR
CONTACTOR

B

M5844

Fig. 22. Tracing the emergency heat and EM. HT. LED circuit.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)

R

H1/C1
ANTICIPATOR

ODT 1

2

FALL

RTD 1
H1

FAN SWITCH

C1

L2
1

EHR 1

RTD 2

W3

3
AUTO
4

ODT 2

ON

AUX. HT.
LED
(GREEN)

5

H2

EHR 2

W2

H2
ANTICIPATOR

X

6

FALL

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

O

HEAT
POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

FAN RELAY

G

EM. HT.

1

RTD 3

RTD 1

OFF

CHANGEOVER
VALVE

E

COOL

EM. HT.
RELAY

CHP

LACO
Y
B

COMPRESSOR
CONTACTOR

M5845

Fig. 23. Tracing the cooling circuit.

19

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)

R

H1/C1
ANTICIPATOR

ODT 1

FALL

1
RTD 1
FAN SWITCH

H1

L2

2

C1

EHR 1

RTD 2

W3

3
AUTO
4

ODT 2

ON

AUX. HT.
LED
(GREEN)

5

FALL

RTD 3

RTD 1

X

6

H2

EHR 2

W2

H2
ANTICIPATOR

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O
HEAT
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

OFF

EM. HT.
RELAY

CHANGEOVER
VALVE

E

COOL
CHP

LACO
Y
COMPRESSOR
CONTACTOR

B

M5846

Fig. 24. Tracing the auto fan circuit.
THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)

R

H1/C1
ANTICIPATOR

ODT 1

2

FALL

RTD 1
H1

FAN SWITCH

C1

EHR 1

ODT 2

AUTO
ON

AUX. HT.
LED
(GREEN)

5

FALL

EHR 2

W2

H2
ANTICIPATOR

H2

RTD 2

W3

3

4

L2
1

RTD 3

RTD 1

X

6

EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G
EM. HT.

O

HEAT
E

OFF
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

COOL

EM. HT.
RELAY

CHP

LACO
Y
B

Fig. 25. Tracing the fan on circuit.

60-2485—8

CHANGEOVER
VALVE

20

COMPRESSOR
CONTACTOR

M5847

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

OPERATION

Heat anticipators add heat during the call for heat. Cooling
anticipators are activated while the air conditioner is off. See
Fig. 28. This heater makes the thermostat think it is warmer than
it really is, and brings it on sooner than the bimetal alone would.

Heat Anticipation/Cool Anticipation
When controlling a heating unit with a thermostat, the
temperature does not remain exactly at the thermostat
setpoint, but varies within a certain temperature range. Heat
anticipation is added to the thermostat to reduce this range.

L1
L2
(HOT)

The anticipator is a small resistive heater in the thermostat
that heats when the system is on (heat mode) or off (cool
mode). The heat produced by the anticipator raises the
internal bimetal temperature slightly faster than the
surrounding room temperature. The thermostat anticipates
the need to shut off the heating system sooner than it would if
affected by room temperature only.

RISE

C1

C1 ANTICIPATOR

There are two types of heat anticipation, adjustable and fixed.
Adjustable anticipation is also called current anticipation. See
Fig. 26. The heater is in series with the mercury switch and
heating primary. The pointer is adjusted to match the current
draw of the primary control, and the correct amount of heat is
added for proper cycle rates.
L1
L2
(HOT)

H1
STAGE 1 HEAT RELAY
M5823

Fig. 26. Adjustable anticipation heater in series with load.
Fixed anticipation is also called voltage anticipation. See
Fig. 27. The heater is in parallel with the primary control and is
not affected by the current draw of the primary. It establishes
the proper cycle rate for any application.

Fig. 28. Internal cooling anticipation schematic.

Interstage Differential
The mercury switch of each stage of heat makes at a slightly
different temperature; that is, the mercury makes the contacts
of the first stage bulb at one temperature, and the second
stage bulb at another temperature. The difference between
these two temperatures is the interstage differential.

Mechanical differential is the difference between the make
and break points of each switch. The mechanical differential
for the T874 is 1°F (0.6°C) between the stages of heating or
between the stages of cooling for most models.

Droop
The addition of anticipator heat to the bimetal causes a control
factor called droop.
As the weather grows colder, the heating appliance must
operate longer and more frequently. More heat must be added
to the bimetal. The bimetal now thinks it is warmer than it
really is, and actual room temperature is controlled at a lower
temperature than the setpoint indicates. At 100 percent heat
load, this droop can be significant.

L1
L2
(HOT)

The C815A Outdoor Reset Thermistor is used in heat pump
systems to minimize droop. Without some method of
countering this situation, the occupant could notice the
temperature offset.

STAGE 1
HEAT RELAY
FALL

H1

M5825

Interstage differential is the difference between the two make
points when the bulbs are controlled by the heating of the
bimetal and the action of the heat anticipator. The interstage
differential is 1.9°F (1°C) between the stages of heating or the
stages of cooling for most models.

H1 ANTICIPATOR

FALL

STAGE 1
COOL RELAY

H1 ANTICIPATOR

Outdoor Reset

M5824

Fig. 27. Fixed anticipation heater in parallel with load.

21

Some T874/Q674 models are intended for use with the
C815A Outdoor Thermistor. The outdoor thermistor provides
significantly improved thermostat performance when
compared to conventional multistage thermostats. The C815A
is usually located in the heat pump condensing unit outdoors.

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

CAUTION
Equipment Damage Hazard.
Due to calibration techniques used for T874
Thermostats with outdoor reset, the C815A Thermistor
must be wired into the system at all times. Failure to
do so will result in serious degradation of performance.

Service and Replacement of C815A Outdoor
Thermistor

THERMISTOR RESISTANCE (ohms)

To check and verify thermistor operation, perform the
following steps:
1. Disconnect wire from T terminal on subbase.
2. Measure resistance with ohmmeter across the T subbase wire and X subbase terminal.
3. Take outdoor temperature measurement at thermistor
location and find correct thermistor resistance on the
chart in Fig. 29.
4. Compare resistance on the chart with measured resistance. Replace C815A if resistance varies more than 15
percent. Contact installing dealer for packaged replacement outdoor thermistor.

A strip of four inserts is included with TRADELINE T874. Drop
a strip into the recessed area behind the scaleplate so
selected LEDs show. Make sure insert is completely seated in
recessed area. Let scaleplate pop back; then set levers to
desired position.
• FILTER LED lights when the filter is clogged and needs
replacement.
• CHECK LED lights when something needs to be checked
or done to maintain efficient operation of system. See
heating system instructions for CHECK LED meaning.
• EM. HT. LED lights when the emergency heat is operating.
• SUPL. HT. LED lights when the supplemental heat is
operating.
• LOCKOUT LED lights when the system is shut down and
needs maintenance.
• AUXILIARY HEAT LED lights when the auxiliary heat is
operating.
• SERVICE or MALFUNCTION LED can have several
meanings. Consult heating system instructions.
LEDs cannot be replaced or added in the field.
LEDS

80

4600
4400
4200
4000
3800
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0

EM.
HEAT FILTER SERV.

AUX
HEAT

50 60 70 80

COOL

C815A THERMISTOR RESISTANCE
R = 400 ohms ± 10% AT 77°F (25°C)

M5830

Fig. 30. T874/Q674 LED location.

Restricted Setpoint (DoD)
The Department of Defense (DoD) models are equipped with
a restricted setpoint feature for fuel efficiency.
-20

0

20

40

60

80

100

120

TEMPERATURE OF THERMISTOR (°F)

Fixed stops are factory-set so setpoint levers cannot be set
above 72°F (22°C) on heating, or below 78°F (26°C) on cooling.

140

M1590A

Fig. 29. Thermistor resistance chart.

Applications

Features
Two of the features of the T874/Q674 include LED indicators
and restricted setpoint.

The T874/Q674 can be applied to standard residential
systems for automatic or manual changeover, to commercial
rooftop applications, or to heat pump applications.

LED Indicators

Changeover on Standard Residential
Systems

The light-emitting diodes (LED) indicators on the subbase
light on command when something specific happens in the
system. See Fig. 30.

In a standard residential heating-cooling circuit, changeover
between heating and cooling can be done either automatically
or manually.

Up to four different LEDs are available. The thermostat has a
clear lens window for viewing each LED. On TRADELINE
models, a small insert is used so the LED function desired can
be selected. This must be done during installation.

Automatic changeover is done by an AUTO position on the
subbase system switch. See Fig. 31. When the switch is in the
AUTO position, the thermostat automatically changes between
heat and cool modes, depending on the indoor temperature.

A blank insert is factory-installed in some T874 models. To
remove it, push both temperature setting levers to the far ends
of the thermostat. Use index fingernail to gently pull out the
scaleplate a fraction of an inch. Turn thermostat upside-down,
and the blank insert falls out.
60-2485—8

22

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

When enthalpy is low enough, the thermostat and a sensor
tell the economizer damper to open to let in cool air from the
outside. When enthalpy is high, the thermostat and sensor tell
the damper to close. No more outside air comes in, so the air
conditioner is used instead.

Heat Pump Application

OFF EM. HT. HEAT AUTO COOL
M5828

Fig. 31. System switching for automatic changeover.
Automatic changeover is frequently used in areas where there
are large temperature differences in 24 hours. Some uses for
the automatic changeover feature are in the southern states
(cool in the morning and hot in the afternoon) and in
commercial applications.
Manual changeover requires a system switch movement to
change the mode. See Fig. 32. Most manual changeover
switches consist of HEAT-OFF-COOL choices. For heating,
switch to HEAT. For cooling, switch to COOL. It is not automatic.
Manual changeover is often used in areas where the
temperature is relatively stable between day and night.

A heat pump system operates much like an air conditioner.
However, the heat pump is capable of moving heat in two
directions; from inside the home to outdoors for cooling, or
from outdoors to inside for heating.
The heat pump can be controlled by separate relay/contactor
components, which are energized or de-energized by the T874.
Changeover between heating and cooling for heat pump
circuits can be accomplished either manually or automatically.
Manual changeover control requires a system switch
movement to change the mode. The reversing valve is
activated by moving the system switch to COOL for cooling or
to HEAT for heating operation.
Automatic changeover is accomplished by one of the mercury
bulb switches in the thermostat. On a system with automatic
changeover on cooling, the changeover valve is energized by
a mercury switch that makes on a temperature rise. On
heating, the changeover valve is energized by a mercury
switch that makes on a temperature fall.
A description of the methods used to control heat pumps
follows.

OFF EM. HT. HEAT COOL
M5829

Space Temperature Sensing Low Voltage
Controls

Fig. 32. System switching for manual changeover.

Commercial Rooftop Application
The T874 can be used as part of a commercial rooftop
application to run mechanical cooling.
An economizer is often used as part of a rooftop application to
save on air conditioning. See Fig. 33.

Control systems for heat pumps usually utilize low voltage
control circuits. The variety of control functions required and
the relative complexity require a versatile and economical
method of control. There are several interlocks and indication
functions that would be more difficult and expensive to wire in
line voltage circuits. Low voltage controls have the precision
and flexibility needed.
The thermostat used is a low voltage device that has good
temperature sensitivity and several manual and automatic
switching capabilities.

OUTDOOR
AIR

Two-Stage Thermostat

H205 OR H705
ENTHALPY
CONTROL

RETURN
AIR

In most installations, the heat pump itself requires auxiliary
heat, usually in the form of electric strip heaters, to carry the
building heating load at design conditions. Since the heat
pump is usually more efficient, the control strategy is to run
the heat pump whenever possible and the auxiliary heat only
when necessary—during very cold weather or if the heat
pump fails. Usually the auxiliary heat is used only below the
balance point (temperature at which the heat pump cannot
handle heating load by itself).

DISCHARGE AIR SENSOR
DOWNSTREAM FROM THE
EVAPORATOR COIL
M5827A

Fig. 33. Typical commercial rooftop economizer
application.

A two-stage thermostat makes this possible. The two stages
make sequentially as the temperature drops. There is a
degree or two between stages so that the second stage (the

Enthalpy is the temperature and humidity of the air. A more
accurate analysis of the suitability for free cooling can be
made by monitoring the enthalpy.
23

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

one controlling the auxiliary heat) makes only when the heat
pump alone cannot handle the load. That is how the strategy
of using the most economical heat first is implemented.

Cycling Rate
Normally, thermostat anticipation is set to cycle a fossil fuel
furnace about five or six times an hour (at 50 percent load).
This provides a reasonable balance between comfort, stability
and economy.
A heat pump, being a mechanical refrigeration system, should
be cycled at a rate of 2-1/2 to 3 times an hour. With a T874,
this is accomplished by setting the anticipator at the total
current draw of the controlled device (the contactor and
possibly the changeover relay or valve). Most likely, the
compressor operates from the first stage of the thermostat.

This is particularly important on the 3-stage T874. The
additional stage means that more droop is introduced when
the system is in operation. That is the reason the TRADELINE
T874W is sold in a package with the outdoor sensor and the
correct subbase.

Outdoor Reset—How it Works
The heater in the thermostat is connected in series with a
thermistor sensor that measures outdoor temperature. See
Fig. 34. In warm weather, the thermistor has very low
resistance, permitting a large current flow in the heater, which
generates a relatively large amount of heat in the thermostat.
In cold weather, the outdoor sensor has high resistance,
which results in low current flow and little or no heat being
added to the thermostat. This raises the control point,
overcoming the effects of droop and interstage differential.

The second stage normally controls the auxiliary heaters. This
heat anticipator can be set for the current draw of the electric
heat primary, and produces good control.

L1
L2
(HOT)

Voltage Anticipation
Although not a specific requirement for heat pumps, several
models of the T874 have voltage heat anticipation instead of
current anticipation.
With voltage anticipation, the amount of heat added to the
thermostat is constant no matter which load is connected to it.
The anticipator realizes a constant voltage and produces a
constant amount of heat during the ON cycle. This allows the
cycling rate to be designed into the thermostat. The heat
pump manufacturer is assured of correct performance
independent of later thermostat adjustments.

RESET
HEATER

C815A
OUTDOOR
THERMISTOR
SENSOR

M5826

Fig. 34. Location of thermistor.

Outdoor Reset

Changeover

Outdoor reset, which a C815A Outdoor Thermistor makes
possible, is sometimes applied in heat pump systems to help
minimize the effect of the differential between stages. It takes
2°F (1.1°C) change in temperature to bring on the second
stage and full heating. Added to a certain amount of droop
under high loads, there can be a large offset between the
setpoint and room temperature.

Changeover between heating and cooing can be
accomplished either automatically or manually, depending on
the application. Changeover can occur in heating or cooling.

Without some method to counteract this situation, the
temperature offset from the setpoint could be as much as 6°F
(3.3°C) under high load conditions. It is not likely that the
occupants accept this variation without making frequent
thermostat setting changes.
Outdoor reset has the effect of raising the setpoint at cold
outdoor temperatures. Then, even with a few degrees droop,
the space temperature stays near the desired setting.
This is done by calibrating the thermostat high by 5°F (3°C)—
the amount of expected offset. This offset compensates for
differential and droop at high load factors so the thermostat
switches at the setpoint. At warm temperatures, heat is added
to the thermostat to compensate for this offset; at cold
temperatures, the extra heat is automatically removed. The
effect is the same as raising the setpoint as the outdoor
temperature goes down.

60-2485—8

24

The changeover valve is energized as long as the subbase
function switch is in the appropriate position when manual
changeover is used. If a system manually changes over on
cooling, the valve energizes whenever the subbase switch is
in the cooling mode.
One of the mercury bulb switches is used for control when the
thermostat has automatic changeover. When the automatic
changeover is in cooling, the changeover valve is energized
when the first stage cooling switch makes. The second stage
switch turns on the compressor.
It is more common with new equipment to find that
changeover occurs with cooling; that is, the changeover valve
is energized to produce cooling.
Whether automatic or manual changeover is used and
whether the reversing valve is energized with cooling or with
heating, a heat pump system can be controlled by the
appropriate T874 Multistage Thermostat.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Low Temperature Lockouts
Some manufacturers of heat pumps have previously controlled
their units so the compressor was locked out below a specified
outdoor temperature. This was done because of the stress
placed on the compressor by the very cold temperatures, and
the fact that efficiency drops off at low temperatures.
Other manufacturers say that although efficiency is low at cold
temperatures, the problem of starting the cold compressor is
the most critical point. It is more important to keep the
compressor running than to shut it off and try to restart it when
the temperature warms up to +10°F (-12°C). Also the
crankcase heater, which can run only when the compressor is
off, compensates for the lower compressor efficiency. So, it is
equitable to let the heat pump run even with a coefficient of
performance (COP) slightly less than one, rather than to turn it
off and have to run the crankcase heater.
NOTE: To determine the COP of a heat pump, use the following formula:

COP =

Btu Out/Btu we pay for or Btuh Capacity
Unit Wattage x 3.413 Btu/Watt

Another factor favoring this control strategy is that newer heat
pump designs maintain a level of efficiency even at outdoor
temperatures well below zero. Some brands do not reach
1.0 COP until -25°F (-32°C).
Virtually all manufacturers now let the heat pump run
continuously rather than lock it out at cold temperatures.

THERMOSTAT
HEAT 2

HEAT 1

COMP.
STAGE 1

COMP.
STAGE 2
OUTDOOR
THERMOSTAT
AUXILIARY
HEAT
M5838

Fig. 35. Two-stage heat pump with two-stage thermostat.
The outdoor thermostat is set at the balance point with both
heat pump stages running. So if the heat pump can control the
heating load down to +20°F (-7°C), the auxiliary heat comes
on with the second stage of the compressor.
In effect, this control strategy changes the heat input of the
second stage, depending on the amount of heat needed.
Additional stages of auxiliary heat can be added with or
without the control of more outdoor thermostats, See Auxiliary
Heat section.
Another way to control a two stage heat pump is with a threestage thermostat. The T874W is designed for this application
as well as others. See Fig. 36.

Heat Pumps with Dual Compressors
Staging residential sized heat pumps is a requirement that
developed from the need to make heat pumps as efficient as
possible. One of the methods used to improve overall
seasonal efficiency is to reduce the amount of time the
machine is operating in a transitional mode. Transitional mode
is starting and stopping in addition to recovering from defrost.
Under light loads, when the heat pump is cycling on and off,
this can be a significant amount of time and can result in a
significant efficiency reduction. Capacity control is one way to
reduce the cycling rate and improve the efficiency.

The advantage of this system is that no auxiliary heat is used
until there is an actual demand from the controlled space.
THERMOSTAT
HEAT 3 HEAT 2

HEAT 1

COMP.
STAGE 1

COMP.
STAGE 2

Additional capacity control methods used on other
refrigeration systems (unloading, multiple compressors) are
not as likely to be seen on residential heat pumps.
With a single-stage heat pump, the compressor is normally
controlled by the first stage and the auxiliary heat by the
second stage. The T874G, N and R Thermostats are used for
this purpose.
With a two-stage compressor, the two thermostat switches
control the individual compressor stages. Auxiliary heat is
controlled along with the compressor stage-two, by the
thermostat second stage. It comes on with the compressor
high speed if an outdoor thermostat—wired in series with it—
is made. See Fig. 35.

AUXILIARY
HEAT
M5837

Fig. 36. Two-stage heat pump with three-stage
thermostat.

Two speed Heat Pump
One way to control capacity is to use a two-speed
compressor. The compressor runs at low speed for stage-one
heating and cooling. The compressor runs at the low speed
instead of cycling the heat pump on and off under some light
load conditions.
The high speed is stage-two cooling. The compressor runs on
high speed when loads increase so the low speed can no
longer handle the cooling load. This reduces cycling rate and
improves capacity.

25

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Defrost Control
In some regions, during half or more of the heating season,
the outdoor coil operates below 32°F (0°C) Frost or ice builds
up on the outdoor coil of a heat pump similarly to the frost
buildup in a household refrigerator. Eventually, this
accumulation of ice interferes with efficient heat transfer from
the outdoor air to the coil and refrigerant. Defrosting is
occasionally required to remove this ice, and restore the heat
pump ability to absorb heat from the air.

L1
L2
(HOT)

TRANSFORMER

THERMOSTAT
HEAT 2

HEAT 1

Defrosting

AUXILIARY
HEAT RELAY

A heat pump defrosts its outdoor coil by temporarily switching
to the cooling mode, which causes hot gas from the
compressor to be directed to the outdoor coil instead of to the
indoor coil so the heat pump is taking heat from the home to
warm up the outdoor coil. Defrosting is the greatest detriment
to heat pump efficiency.

Defrost Control Functions
Besides changing over to the cooling mode, defrosting
requires several more control initiated actions that follow.
OUTDOOR FAN
When defrosting has begun, it is standard practice to turn off
the outdoor fan to speed up the melting process. A separate
defrost relay is required to control that fan. See Fig. 37. Other
contacts can be needed on the defrost relay to power the
changeover valve or power part of the auxiliary heat.
CONTACTOR

DEFROST
RELAY
CONTACT

COMPRESSOR
MOTOR

M5835

Fig. 38. Auxiliary heat with defrost control.
WHEN TO DEFROST
Timely defrosting is an essential component of effective heat
pump operation. Failure to defrost often enough permits too
much ice to accumulate on the coil. At the very least, this
hurts efficiency; at worst, it results in compressor damage.
Insufficient defrosting is a condition the heat pump
manufacturer wants very much to avoid.
A 50 percent reduction in outdoor airflow is the maximum that
would be tolerated. So the designer of a heat pump would
select a control point that puts the system into defrost when
airflow through the outdoor coil approaches half its normal
level. Restricted airflow causes a greater load on the
compressor; the outdoor coil runs colder, suction pressure is
lower and the motor runs hotter.
At the other end of the scale, defrosting too often hurts the
overall energy efficiency of the system. Consider that in terms
of heating the building, defrosting is a big loss. Not only does
the system stop heating, but it actually moves heat out of the
building. If electric strip heat is used, it is a further waste
because its COP is 1.0 and not the 2.0 or more COP realized
if the heat is provided by the heat pump.

CONTROLLED BY OUTDOOR
DEFROST RELAY FAN MOTOR

So, concern for equipment safety suggests fairly frequent
defrosting while economy of operation argues for fewer
defrost cycles. Since the equipment manufacturer chooses, the
balance is usually tipped in favor of more frequent defrosting to
avoid the possibility of damaging the compressor.

M5839

Fig. 37. Outdoor fan with defrost control.
AUXILIARY HEAT DURING DEFROST
Most pump manufacturers bring on some auxiliary heat during
defrost, although this is not a universal practice. Some rely on
the second stage of the thermostat to call for auxiliary heat as
needed. Since the heat pump is operating in the cooling mode
to defrost, it is delivering cold air to the living space. Auxiliary
heat is used to offset this cooling. It requires another normally
open contact on the defrost relay. See Fig. 38.

Auxiliary Heat
Except in warm climates, all air-to-air heat pump installations
require auxiliary heat capability. Electric resistance heaters
can provide this auxiliary heat.
The electric heaters (sometimes called strip heaters) usually
are supplied in 5 kW units or strips (about 17,000 Btu). The
indoor unit of the heat pump is designed to accommodate
various electric heat units so it can be used in variously sized
buildings in different parts of the country.

Two-Stage Thermostat
The most common heat pump control strategy is for the
thermostat first stage to switch the compressor and the
second stage to switch the auxiliary heat. See Fig. 39.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

The disadvantage of this system is that it can require several
outdoor thermostats. Also, since the unit is operating most
often at nearly full capacity, the thermostat is on longer which
results in more droop, with a little more offset from the
thermostat setpoint.

THERMOSTAT
HEAT 2

HEAT 1

COMPRESSOR
CONTRACTOR

CONTROLS
AT 65°F (18°C)

AUXILIARY
HEAT RELAY

CONTROLS
AT 63°F (17°C)

In addition, the capacity is tied to theoretical load, based on heat
loss calculations. Normally this is very close to the actual load,
but there are times where the second stage is switched on too
soon (no harm done) or too late (the building gets cold).

M5836

Fig. 39. Auxiliary heat in two-stage thermostat.
This method keeps the auxiliary heat off until the heating load
is large enough to demand 100 percent heat pump operation.
That demand is measured by the thermostat and is the actual
heat requirement of the space. The two-stage thermostat
requires about a 2°F (1.1°C) room temperature drop to bring
on the second stage.

Stage or Time Modulated Control
There are two different ways to control auxiliary heat, staged
or time modulated control.

Outdoor thermostats are used to switch additional increments
of electric heat into the thermostat circuit as the outdoor
temperature gets lower. All increments of auxiliary heat are
still controlled by stage-two of the thermostat but only if the
outdoor temperature requires the additional capacity. See
Fig. 40.

The T874 Thermostat produces time modulated control, which
is the on time of the thermostat changing during each cycle as
the load changes. The on time of the heating system is
directly proportional to the heating load of the building. As an
example of the quality of time modulated control, consider the
typical gas furnace. It can have a capacity of 100,000 Btu
(293 kW), which is controlled On-Off. The output is 100,000 Btu
(293 kW) or nothing. A quality thermostat controls so closely that
the occupants rarely detect changes in room temperature.
The same is true with 50,000 or 60,000 Btu (146.5 or
178.8 kW) of heat pump auxiliary electric heat. The T874 can
provide the same high quality control.
This scheme also eliminates the need for outdoor thermostats
and thus offers the manufacturer an opportunity to reduce unit
cost. One disadvantage is that a thermostat jiggler can be
demanding more kW of strip heat when chilly.
The method any particular manufacturer selects depends on
which arguments it finds persuasive and the opinions of its
distributors and dealers.

Three-Stage Thermostat
THERMOSTAT
HEAT 2

A definite improvement in quality of control and economy can
be achieved with a three-stage thermostat (T874W), which is
especially true with heat pumps using dual compressors.

HEAT 1

Three-stage control permits both the heat pump and the
auxiliary heat to be tied directly to the demand of the
controlled space. With a two-stage compressor, maximum
(100 percent) heat pump operation is required before auxiliary
heat is brought on.

COMPRESSOR
CONTACTOR

AUXILIARY
HEAT RELAY 1
20°F
(-7°C)
OUTDOOR
THERMOSTATS

Emergency Heat

AUXILIARY
HEAT RELAY 2

Some provision is generally required to back up the compressor
in the event of a failure during the heating season. In fact, it is
quite common to find that local building codes or electric utilities
require that a specified percent of the building heating
requirements be available from emergency heat—a source
other than the heat pump compressor. Almost universally, the
source is electric resistance heaters. Typically, the requirement
is for 70 or 80 percent of the building heating needs.

5°F
(-15°C)
AUXILIARY
HEAT RELAY 3
M5834

Fig. 40. Outdoor thermostats for auxiliary heat.
The rationale for this system is that it very closely matches the
system capacity to the heating load of the building. By
calculating the heat loss of a building, the installing contractor
can pick the theoretical outdoor temperature at which to
permit each additional unit of electric heat to be operated by
the second stage of the room thermostat.

Switching to Emergency Heat
Conventional heat pump control (thermostat logic) usually
includes a manual subbase switch to bring on the emergency
heat.
In one control strategy, the emergency heat relay is turned on
by the EM.HT. selector switch on the thermostat subbase. The
compressor is prevented from running. The electric heaters
are cycled as they normally would be by the second stage of

27

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

the thermostat. A set of contacts on the emergency heat relay
is used to bypass each outdoor thermostat so that all electric
heat is under immediate thermostat stage-two control. So the
emergency heat relay simply bypasses the outdoor
thermostats. See Fig. 41.
In the second method, the emergency heat relay is cycled
directly by the thermostat mercury bulb. In this hookup, the
relay is controlled by the thermostat first stage. The
emergency heat relay energizes all of the auxiliary heat relays
on a call for heat. See Fig. 42.

Crankcase Heat
In any mechanical refrigeration system, refrigerant tends to
migrate to the coldest part of the equipment and condense
there. In a heat pump, this coldest spot could be the compressor
because it is usually outdoors. In addition, the oil in the compressor crankcase is capable of absorbing a high concentration
of refrigerant. On compressor startup, there are two risks: (1) the
liquid refrigerant, which is noncompressible, can be drawn into
the cylinder, and (2) considerable oil can be entrained in the
refrigerant and swept out of the crankcase through the
changeover valve and dispersed in the piping and coils.

So the emergency heat is controlled by the first stage of the
thermostat. The emergency heat relay energizes all of the
electric strip heaters so the heat and the indoor fan come on
together as soon as the first stage calls for heat.

So the migration of refrigerant to the crankcase is undesirable
because it can interfere with system lubrication and because the
liquid refrigerant must be kept from going through the compressor.

With the first method, the fan remains on (being controlled by
the first stage of the thermostat) and the electric heaters cycle
on and off with the second stage.

Adding a crankcase heater creates enough temperature
differential to prevent this migration because the compressor
is no longer the coldest part of the system so refrigerant does
not migrate to it.

In either case, a subbase indicator light is turned on whenever
the function switch is in the emergency heat (EM.HT.) position.

Another very simple method of detecting a compressor failure
has been developed. It uses the voltage developed across the
capacitor in a permanent split capacitor compressor motor.

THERMOSTAT
FUNCTION HEAT 2
SWITCH

Compressor Fault Relay

HEAT 1
COMPRESSOR

The principle involved is that virtually all serious problems
reduce the voltage across the motor capacitor. By carefully
selecting the correct coil voltage, the normally closed relay
does not pull in unless the proper voltage builds up across the
capacitor, which brings on the SERVICE LED. See Fig. 43.

AUXILIARY
HEAT RELAY 1
OUTDOOR
THERMOSTAT
AUXILIARY
HEAT RELAY 2

EMERGENCY HEAT
RELAY CONTACT

Here is how it works:
• On a call for cooling, the thermostat makes R to Y, the
contactor coil is powered, and the compressor motor turns on.
• At the same time, the indicator light is energized.
• As the motor gets up to speed—about one second, the
fault relay sees enough voltage to pull in. Its normally
closed contact opens and the indicator light goes out.
• Anything that prevents the motor from running prevents the
fault relay from pulling in.

EMERGENCY
HEAT RELAY
M5833

Fig. 41. Emergency heat relay that bypasses
the outdoor thermostats.

COMPRESSOR MOTOR

L1

24 V

FAULT RELAY

RUN R

THERMOSTAT
FUNCTION HEAT 2
SWITCH

C

HEAT 1

CAP.

L3
EMERGENCY
HEAT RELAY
CONTACT

START

S

COMPRESSOR

Y

R

L

L2

X

AUXILIARY
HEAT RELAY

L1
(HOT)
RISE

EMERGENCY
HEAT RELAY

LED

M5832

CONTACTOR

Fig. 42. Emergency heat relay that energizes all of the
auxiliary heat relays on a call for heat.

THERMOSTATSUBBASE

M5831

Fig. 43. Compressor fault relay schematic.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

CROSS REFERENCE

3.

The following section lists the current T874 Trade replacements for T872 and T874 Multistage Thermostats. It also lists
the Q674 Trade replacements for Q672 and Q674 Subbases.

4.
5.
6.

All thermostats listed carry the Honeywell logo unless
otherwise noted.
When using the Cross Reference Charts, refer to the following
instructions:
1. Locate and identify the existing thermostat and subbase
model.
2. Refer to the Model Number column to find the model
that matches the existing thermostat and subbase.

7.

The Description column identifies certain characteristics
of the existing device.
The Trade Replacement column identifies the correct
replacement device.
The Remarks column lists any characteristics or adjustments to be made on the Trade replacement model.
The Fig. No. column lists the wiring hookup used for the
specific model number. The wiring diagrams follow the
Cross Reference section.
Refer to the circuit illustration that corresponds with the
appropriate number. This figure illustrates the internal
electric circuit for the desired model number.

Table 6. T872-T874 Thermostat Cross Reference.
Model Number
T872A

a

T874 Trade
Replacementa

Description

Remarks

1-stage heat, 1-stage cool

A1006

Standard OEM

T874A1036

A1014

72-78°F (22-26°C) stop; locking cover; no
thermometer

T874A1010

A1022

Heat anticipator set at 0.45A

T874A1036

A1030

0.4A heat anticipator setting

T874A1036

A1048

TRADELINE

T874A1036

A1055

AAF logo; locking cover

T874A1036

A1063

Climatrol logo

T874A1036

A1071

Lennox logo; 0.5A heat anticipator setting

T874A1036

A1089

Melco logo

T874A1036

A1097

Westinghouse logo

T874A1036

A1105

Amana logo; 1.2A heat anticipator setting

T874A1036

A1113

Trane logo

T874A1036

A1121

Airtemp (Chrysler) logo

T874A1036

A1139

Singer logo; no. 02005384

T874A1036

A1147

American Standard logo

T874A1036

A1154

Carrier logo and color; no. HH07AT074

T874A1036

A1162

General Electric logo; no. AY28X097

T874A1036

A1170

Sears logo; no. 4291441

T874A1036

A1188

Command-Aire logo

T874A1036

A1196

Singer logo; Celsius scale; no. 02005521

T874A1036

A1204

Carteret logo

T874A1036

A1212

General Electric; no. AY28X114; 72-78°F
(22-26°C) stop

T874A1010

A1220

Singer logo; no. 050240-01

T874A1036

A1238

Celsius scale

T874A1036

A1246

TRADELINE; locking cover and adjustable locking T874A1150
lever stops

A1253

Trane Comfort Corp

T874A1036

A1261

TRADELINE; 72-78°F (22-26°C) stop; locking
cover; no thermometer; meets DoD specs

T874A1176

Use T874A1176 for Dept. of
Defense (DoD) application.

Use T874A1176 for Dept. of
Defense (DoD) application.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

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Table 6. T872-T874 Thermostat Cross Reference.
Model Number

Remarks

A1279

General Electric logo; no. AY28X114A; 75°F stop; T874A1010
locking cover; no thermometer.

Use T874A1176 for Dept. of
Defense (DoD) application.

A1287

General Electric; no. AY28X097A; fan current
T874A1036/
shunt for auto fan in heating; heat anticipator set at Q674B1018
0.4A.

Set thermostat stage 1 heat
anticipator for total of fan and stage
1 primary control current draw.

A1295

Lennox; Celsius scale

T874A1036

A1303

Lennox logo; no. 64A0601; meets DoD specs

T874A1176

A1311

Envirotron special; Celsius scale

T874A1010

A1329

Carrier logo; Celsius scale; no. HH07AT074C

T874A1036

A1337

Square D; no. HCD-3; heat anticipator set at 0.2A T874A1036

A1345

TRADELINE; Celsius scale

T874A1010

A1352

Heat anticipator set 1.2A

T874A1036

A1360

Friedrich logo; heat anticipator set at 0.2A

T874A1036

A1378

Wesco logo; heat anticipator set at 0.8A

T874A1036

T872B

1-stage heat, 2-stage cool

B1005

Standard OEM

T874B1019

B1013

0.4A heat anticipator setting

T874B1019

B1021

TRADELINE

T874B1019

B1039

Westinghouse logo

T874B1019

B1047

American Standard logo

T874B1019

B1054

Climatrol logo

T874B1019

B1062

Carrier logo

T874B1019

B1070

Trane logo

T874B1019

B1088

Fedders logo

T874B1019

B1096

Climatrol logo

T874B1019

B1104

Carteret logo

T874B1019

B1112

Singer logo; no. 050240-03

T874B1019

B1120

Celsius scale

T874B1019

B1138

Singer logo; no. 02005711; locking cover and
lever.

T874B1019

B1146

Lennox logo; no. P-8-8895

T874B1019

B1153

Lennox logo; Celsius scale

T874B1019

T872C

a

T874 Trade
Replacementa

Description

2-stage heat, 1-stage cool

C1004

Standard OEM

T874C1018

C1012

Heat anticipator set at 0.4A

T874C1018

C1020

72-78°F (22-26°C) stop; locking cover; no
thermometer; 42-88°F (6-31°C) setpoint range.

T874C1141

C1038

TRADELINE

T874C1018

C1046

American Standard logo

T874C1018

C1053

Friedrich logo

T874C1018

C1061

Lennox logo; no. P-8-8896

T874C1018

C1079

Westinghouse logo; stage 1 heat anticipator set at T874C1018
0.75A; stage 2 anticipator set at 1.2A

C1087

Fast cycle performance on both heat stages;
anticipator range 0.12-0.6A

T874C1018

C1095

Payne logo; no. 0.1-0.175

T874C1018

Use T874C1141 for Dept. of
Defense (DoD) application.

Adjust anticipator faster for correct
performance.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 6. T872-T874 Thermostat Cross Reference.
Model Number

a

T874 Trade
Replacementa

Description

C1103

Amana logo; anticipator set at 1.2A

T874C1018

C1111

Airtemp (Chrysler) logo

T874C1018

C1129

Day and Night logo; no. 0.1-0.174

T874C1018

C1137

Fast cycle performance on both heat stages

T874C1018

C1145

Rheem logo

T874C1018

C1152

Ruud logo

T874C1018

C1160

Climatrol logo

T874C1018

C1178

Wesco logo

T874C1018

C1186

Sears logo

T874C1018

C1194

First Co. logo

T874C1018

C1202

Carrier logo

T874C1018

C1210

Carrier logo; Celsius scale

T874C1018

C1228

0.4A heat anticipator setting

T874C1018

C1236

Carrier logo; no. HH07AT070

T874C1018

C1244

Fraser-Johnson logo

T874C1018

C1251

Trane logo

T874C1018

C1269

Fedders logo

T874C1018

C1277

Climatrol special

T874C1018

C1285

Autogas logo

T874C1018

C1293

Fedders logo

T874C1018

C1301

Climatrol logo

T874C1018

C1319

Command-Aire logo

T874C1018

C1327

Melco logo; lock cover and levers

T874C1018

C1335

Singer logo (Carteret)

T874C1018

C1343

Singer logo; no. 050240-04

T874C1018

C1350

Celsius scale

T874C1018

C1368

12°F (67°C) differential between heat 1 and
heat 2

T874C1125

C1376

AAF logo; locking cover; 72-78°F (22-26°C) stop

T874C1018
T874C1018

C1384

Servel logo

C1392

TRADELINE; fast cycle performance on both heat T874C1018
stages.

C1400

72-78°F (22-26°C) stop; locking cover; no
thermometer; meets DoD specs

T874C1141

C1418

Solaron logo

T874C1018

C1426

Lennox logo; no. 42C04; four LEDs

None

C1434

Carrier logo; no. HH07AT070C; Celsius scale

T874C1018

C1442

Goettl logo

T874C1018

C1459

Goettl logo; used with Q672N1001, N1019

None

C1467

Lennox logo; Celsius scale

T874C1018

C1475

Tappan logo; no. 080-13708-37

T874C1018

C1483

Fasco logo; no. 1230-8161

T874C1018

C1491

Lennox logo; no. 64A0501; locking cover; no
thermometer; meets DoD specs

T874C1141

Remarks

Adjust anticipator faster for correct
performance.

Adjust anticipator faster for correct
performance.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

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Table 6. T872-T874 Thermostat Cross Reference.
Model Number

T874 Trade
Replacementa

Description

C1509

Fedders logo; used with Q672L1102

Y594R1425

Wiring differences (old=new): C=X,
K=E; remove Y-W1 jumper.

C1517

Climatrol logo; used with Q672L1102

Y594R1425

Wiring differences (old=new): C=X,
K=E; remove Y-W1 jumper.

C1525

Square D logo; no. HCD-2

T874C1018

C1533

Airtemp logo

T874C1018

C1541

Airtemp logo; used with Q672L1102

Y594R1425

Wiring differences (old=new): C=X,
K=E; remove Y-W1 jumper.
Replacement has °F scaleplate.

C1566

TRADELINE; Celsius scale

T874C1018

C1574

Whalen special; used with Q672B1269

None

C1582

Lennox; meets DoD

None

C1590

Singer; 8°F (4.4°C) differential between stage
1 and stage 2

T874C1125

Replacement has 2°F (1° C)
differential between H1 and H2.

C1608

Singer logo; no. 02005784 8°F (4.4°C) differential T874C1125
between stage 1 and stage 2

Replacement has 2°F (1°C)
differential between H1 and H2.

C1616

Celsius scale; stop set at 23°C

Add 4074ECK adjustable stop.

None

C1624

Heat Wave logo; no. 0360-116

T874C1018

C1632

York logo; heat anticipator set at 0.2A

T874C1018

C1640

Heat anticipator set at 0.4A

T874C1018

C1665

Wesco logo; heat anticipator set at 0.8A

T874C1018

C1673

Wards logo; used with Q672B1285, B1293

Gas systems:
T874C1018/
Q674B1034
Electric systems:
T874C1018/
Q674B1075

C1681

Lechauffage Urbain logo; Celsius scale

T874C1018

C1699

Duotherm logo; used with Q672E1068 or
Q672F1000

T874C1018

C1707

Sigler logo; used with Q672N1027

None

C1715

Westinghouse logo

T874C1018

T872D

a

Remarks

Adjust anticipator faster for correct
performance.

See subbase description for
replacement information.

2-stage heat, 2-stage cool

D1003

Standard OEM

T874D1165

D1011

TRADELINE

T874D1165

D1029

Westinghouse logo

T874D1165

D1037

Climatrol logo

T874D1165

D1045

Lennox logo; no. P-8-8897; used with Q672E1191. T874D1165

D1052

York logo

D1060

Singer logo; no. 02005385

T874D1165

D1078

Rheem logo

T874D1165

T874D1165

D1086

Rudd logo

T874D1165

D1094

York logo; locking cover

T874D1165

D1102

American Standard logo

T874D1165

D1110

ITT logo

T874D1165

D1128

Carrier logo

T874D1165

D1136

No anticipator on stage 1 cool; used with
Q672C1029

T874D1165

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

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Table 6. T872-T874 Thermostat Cross Reference.
Model Number
D1144

Carrier logo; no. HH07AT072

T874D1165

D1151

General Electric logo; no. AY28X098; 0.4 heat
anticipator setting

T874D1165

D1169

Airtemp (Chrysler) logo; used with Q672E1118

T874D1165/
Q674E1049

D1177

Trane logo

T874D1165

D1185

Dunham-Bush logo

T874D1165

D1193

Fedders logo

T874D1165

D1201

Climatrol logo

T874D1165

D1219

Command-Aire logo

T874D1165

D1227

Singer logo; no. 02005522; Celsius scale

T874D1165

D1235

Singer logo; (Carteret)

T874D1165

D1243

Friedrich logo

T874D1165

D1250

Singer logo; no. 050240-02

T874D1165

D1268

Airtemp logo

T874D1165

D1276

Celsius scale

T874D1165

D1284

Solaron

T874D1165

D1292

Tokyo Carrier logo; no. HH07AT072C; Celsius
scale

T874D1165

D1300

SUPER TRADELINE

T874D1165

D1318

General Electric logo; no. AY28X098A; fan current T874D1165/
Q674B1075
shunt for auto fan in heating.

D1326

General Electric logo; locking cover 72-78°F
(22-26°C) stop; fan current shunt for auto fan in
heating.

T874D1165

D1334

Lennox logo; Celsius scale

T874D1165

D1342

Tappan logo; no. 080-13708-32

T874D1165

D1359

Singer logo; no. 02005740; Celsius scale; 6.6°C
differential between H1 and H2.

T874D1165

D1367

Friedrich logo; no. 600-580-23

T874D1165

D1375

Singer logo; no. 02005713; Celsius scale; controls None
2 separate heat/cool circuits; used with
Q674G1017

D1383

TRADELINE; Celsius scale

D1391

Singer logo; no. 02005712; controls two separate None
heat/cool circuits; used with Q674G1017

Remarks

Wiring differences (old=new):
A=W1; set H1 anticipator to 1.2A.

Only 2°F (1°C) differential between
H1 and H2.

T874D1165

D1409

12°F (7°C) differential between H1 and H2

T874D1165

D1417

Fedders logo

T874D1165
T874D1165

D1425

Climatrol logo

D1433

Singer logo; no. 02005785; 8°F (4.4°C) differential T874D1165
between H1 and H2

D1441

American Air Filter

T874D1165

D1474

Carrier; no. HH07AT072-03; Celsius scale

T874D1165

T872E

a

T874 Trade
Replacementa

Description

2-stage cool

E1002

Standard OEM

T874E1016

E1010

TRADELINE

T874E1016

E1028

Westinghouse logo

T874E1016

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

33

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 6. T872-T874 Thermostat Cross Reference.
Model Number
E1036

American Standard logo

T874E1016

E1044

York logo; locking cover

T874E1016

E1051

ITT logo

T874E1016

E1069

Climatrol logo

T874E1016

E1077

Airtemp (Chrysler) logo

T874E1016

E1085

Lennox logo

T874E1016

E1093

Trane logo

T874E1016

E1101

Dunham-Bush logo

T874E1016

E1119

Fedders logo

T874E1016

E1127

Climatrol logo

T874E1016

E1135

General Electric logo; no. AY28X108

T874E1016

E1143

Lennox logo; Celsius scale

T874E1016

E1150

Celsius scale

T874E1016

E1168

Airtemp logo

T874E1016

T872F

2-stage heat

F1001

Standard OEM

F1019

TRADELINE

T874F1015

F1027

Lennox logo; fast cycle heat anticipator

T874C1018

F1035

Luxaire logo; fast cycle performance on both heat T874C1018
stages.

F1043

York logo; locking cover; used with M839.

Remarks

T874F1015

M839 draws 0.72A; set adjustable
heat anticipator to setting of 0.9A
for proper cycle rate.

T874C1018

F1050

Raehco logo

T874F1015

F1068

Fast cycle performance on both heat stages.

T874C1018

F1076

Wesco logo

T874F1015

F1084

Lennox logo

T874F1015

F1092

Auto Gas logo

T874F1015

F1100

Celsius scale

T874F1015

F1118

Lennox logo; Celsius scale

T874F1015

F1126

Stages 1 and 2 heat electrically isolated; used with None
Q672D1002

F1134

Square D logo; HCD-4

T874F1015

F1159

Wesco logo; heat anticipator set at 0.8A

T874F1015

F1167

York logo

T874F1015

F1175

Oneida Heater logo; no. 30A0287-01; used with
Q672K1012.

T874F1015/
Q674K1026

T872G

a

T874 Trade
Replacementa

Description

Heat pump models; 2-stage heat,
1-stage cool, 1-stage changeover.

G1000

Fast cycle performance stage 2 heat; fixed
Y594G1252
anticipator stage 1 heat and cool; changeover with
cooling; used with Q672F1018.

Wiring differences (old=new):
W=W2, X1=X.

G1018

Y594G1393
Adjustable anticipator stage 2 heat; fixed
anticipator stage 1 heat and cool; changeover with
cooling; used with Q672E1027.

Wiring differences (old=new):
Y1=O, Y2=Y.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 6. T872-T874 Thermostat Cross Reference.
Model Number

a

T874 Trade
Replacementa

Description

Remarks

G1026

Lennox logo; fast cycle performance; stage 2 heat; None
fixed anticipator stage 1 heat and cool;
changeover with cooling; used with Q672E1019,
F1067.

See subbase description for
replacement information.

G1034

Westinghouse logo; adjustable anticipator stage 2 Y594G1252
heat; fixed anticipator stage 1 heat and cool;
changeover with cooling; used with Q672F1091,
F1141, F1257 or Q672J1013, J1062.

Wiring differences (old=new):
W=W2.

G1042

York logo; fixed anticipator on all stages heat and Y594G1567
cool; changeover with cooling; used with
Q672J1021.

G1059

TRADELINE; no anticipator stage 2 heat; fixed
Y594G1161
anticipator stage 1 heat and cool; changeover with
cooling; used with Q672J1039 outdoor reset.

Designed for use on General
Electric heat pumps.

G1067

Lennox logo; no. P-8-11222; fast cycle
performance; stage 2 heat; fixed anticipator stage
1 heat and cool; changeover with cooling; used
with Q672E1142, F1083.

See subbase description for
replacement information.

G1075

Carrier logo; adjustable anticipator stage 2 heat;
fixed anticipator stage 1 heat and cool;
changeover with cooling; used with Q672J1054,
L1052.

See subbase description for
replacement information.

G1083

Adjustable anticipator stage 2 heat; fixed
Y594G1252
anticipator stage 1 heat and cool; changeover with
cooling; includes shunt to bypass stage 2
anticipator with auxiliary heat relays; used with
Q672F1158.

G1091

Lennox logo; same as T872G1026 except meets
DoD specs.

See subbase description for
replacement information.

G1109

Y594G1252
Tappan logo; no. 080-13708-52; adjustable
anticipator stage 1 heat and cool; changeover with
cooling; used with Q672F1117.

Wiring differences (old=new): C=X.

G1117

Changeover; used with Q672F1125.

Wiring differences (old=new): C=X.

G1125

Lennox logo; no. 63A0401; Celsius scale; isolated None
auxiliary heat power circuit; fast cycle anticipator
stage 2 heat.

G1133

Rheem logo; no. RXMT-B71; adjustable
anticipator stage 2 heat; fixed anticipator stage 1
heat and cool; changeover with cooling; includes
shunt to bypass stage 2 anticipator with auxiliary
heat relays; used with Q672F1158, F1232.

G1141

Ruud logo; adjustable anticipator stage 2 heat;
Y594G1252
fixed anticipator stage 1 heat and cool;
changeover with cooling; includes shunt to bypass
stage 2 anticipator with auxiliary heat relays; used
with Q672F1158.

G1158

Carrier logo; same as T872G1075. Except DoD
styling.

G1166

BDP used with Q672F1125.

Y594G1252

Wiring differences (old=new): C=X.

G1174

BDP used with Q672F1125.

Y594G1252

Wiring differences (old=new): C=X.

G1182

Carrier; no. HH07AT071C; Celsius scale; used
with Q672L1052, J1054.

G1190

Tappan; no. B13708-57; used with Q672L1078 for None
8 and 10 ton heat pumps with 2 compressors.

Y594G1252

Y594G1252

See subbase description for
replacement information.

See subbase description for
replacement information.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

35

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 6. T872-T874 Thermostat Cross Reference.
Model Number

T874 Trade
Replacementa

Description

G1208

Marvair logo; special for Crispaire; used with
Q672F1166, F1323.

Y594G1393

G1216

Janitrol logo; no. 26G05; stage 2 heat anticipator
set at 1.2A; used with Q672F1117.

Y594G1252

G1224

TRADELINE; adjustable anticipator stage 2 heat;
fixed anticipator stage 1 heat and cool;
changeover in cool; used with Q672F1208.

Y594G1419

G1232

Heat Wave (Southwest Mfg.) logo; stage 2 heat
anticipator set at 1.2A; used with Q672F1224.

G1240

Lennox; fast cycle anticipator stage 2 heat; used
with Q672F1240.

None

G1257

Carrier logo; no. HH07AT073; used with
Q672L1169 (HH93AZ071).

None

G1265

Addison logo; used with Q672F1265.

Y594G1252

G1273

Carrier logo; (DoD model); 68°F (20°C) maximum
heating; 78°F (26°C) minimum cooling; used with
Q672L1052, J1054

G1281

Wesco logo; used with Q672F1265.

Y594G1252

G1299

York logo; meets DoD specs; used with
Q672L1177.

Y594G1567

G1307

Carrier; no. 38EQ1900; Celsius; used with
Q672J1054, L1052.

G1315

Luxaire special; stage 2 heat anticipator set to
1.2A; used with Q672F1281.

Y594G1252

G1323

Lennox special; used with Q672L1201 and
C815A1013.

None

G1331

York; used with Q672J1021.

Y594G1567

Wiring differences (old=new):
X=X1, L=X2, W=E; Y1-W1 and Y2W2 jumpers required.

G1356

Westinghouse; used with Q672L1219.

T874D1165/
Q674F1022

Wiring differences (old=new):
X=X1, L=X2, W=E; Y1-W1 and Y2W2 jumpers required.

Wiring differences (old=new): C=X.

Wiring differences (old=new): C=X.
See subbase description for
replacement information.
Wiring differences (old=new): C=X.

See subbase description for
replacement information.

G1364

York; used with Q672D1077.

None

G1372

Tappan/Janitrol logo; no. B-13708-521;
used with Q672F1117.

Y594G1252

G1398

York logo; no. 025-21454C; used with Q672J1021. Y594G1567

T872H

Wiring differences (old=new): C=X.

Heat pump model; 1 stage heat,
1 stage cool, 1 stage changeover.

H1009

Command-Aire logo; fixed anticipator stage 1 heat Y594H1012
and cool; changeover with cooling; used with
Q672C1086.

H1017

Friedrich logo.

Y594H1012

H1025

Friedrich logo; Celsius.

Y594H1012

T872M

1 stage heat, 1 stage cool with stage 2 heat factory
set at 60°F (16°C).

M1003

Standard OEM; used with Q672D and external
switching means.

T872N

Heat pump model; 2-stage heat, 1-stage cool plus
changeover, changeover in heat mode.

N1002
a

Remarks

T874C1125

T874C1125 has 12°F (6.7°C)
differential between stage 1 and
stage 2 heat.

None

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

60-2485—8

36

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 6. T872-T874 Thermostat Cross Reference.
Model Number
N1010

Williamson logo; adjustable anticipator stage 1
and 2 heat; fixed anticipator stage 1 cool; used
with Q672F1133 or F1315.

T874N1016/
Q674F1220

N1028

TRADELINE heat mode changeover; used with
Q672F1216.

T874N1016

N1036

Bard; used with Q672F1299.

T874N1016/
Q674F1220

N1044

Thermotron logo; 1st stage changeover heat
mode; used with Q672F1299.

T874N1016/
Q674F1220

T872Q

Remarks

1-stage heat; used with another T872 for heating
setback.

Q1009

Standard OEM

T874C1125

Q1017

York logo

T874C1125

Q1025

ITT logo

None

Q1033

Lennox logo; no. P-8-8899.

None

Q1041

Lennox logo; no. 63A6401.

None

T872R

a

T874 Trade
Replacementa

Description

Replacement only good for
1-stage heat and 1-stage cool
applications.

Heat pump model; 2-stage heat, 1-stage cool,
manual changeover.

R1008

Y594R1425
Fixed anticipator stage 1 heat and cool; no
anticipator stage 2 heat; changeover with cooling;
used with Q672B1046.

Wiring differences (old=new):
W=W2; W1-Y1 jumper required.

R1016

Addison same as T872R1008; used with
Q672B1103.

Wiring differences (old=new):
W=W2; W1-Y1 jumper required.

R1024

Lennox logo; fast cycle stage 2 heat; fixed
anticipator stage 1 heat and cool; changeover with
cooling; used with Q672B1160 and Q672L1003.

R1032

York logo; fixed anticipator stage 1 and 2 heat and Y594R1664
stage 1 cool; changeover with cooling; used with
Q672L1011.

R1040

Lennox logo; fast cycle stage 2 heat; fixed
anticipator stage 1 heat and cool; isolated stage 2
heat switch; changeover with cooling; used with
Q672B1202 no. P-8-11221, Q672L1029

R1057

TRADELINE; fixed anticipator stage 1 heat and
cool; no anticipator stage 2 heat; changeover on
cooling; used with Q672L1037; outdoor reset.

Y594R1763

R1065

Adjustable anticipator stage 2 heat; fixed
anticipator stage 1 heat and cool; changeover on
cooling; used with Q672L1045.

Y594R1243

R1073

Lennox logo; no. 63A0301; Celsius scale;
separate auxiliary heat power circuit; fast cycle
stage 2 heat antic.

None

R1081

Ruud logo; same circuit as T872R1065; used with Y594R1243
Q672L1045, L1136.

R1099

Dunham Bush special; used with Q672L1060,
L1383.

Y594R1243

R1107

Rheem; no. RXMT-B70; used with Q672L1045,
L1136.

Y594R1243

R1115

Friedrich logo; fixed anticipator; used with
Q672B1244, L1086.

Y594R1425

See subbase description for
replacement information.

See subbase description for
replacement information.

Designed for use on General
Electric heat pumps. Wiring
differences (old=new): A=T.

See subbase description for
replacement information.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

37

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 6. T872-T874 Thermostat Cross Reference.
Model Number

Remarks

R1123

York logo; no. 025-21453C; Celsius scale.

R1131

Lennox logo; separate auxiliary heat power circuit; None
fast cycle stage 2 heat anticipator; outdoor reset;
used with Q672L1144, C815A1013.

R1149

Westinghouse logo; adjustable stage 2 heat
anticipator; cooling changeover; fixed anticipator
stage 1 heat and cool; used with Q672L1110,
L1128, L1151.

Y594R1243

Wiring differences (old=new):
W=W2.

R1156

Marvair logo; used with Q672L1094, L1250.

Y594R1243

Replacement has auto fan in
Emergency Heat mode.

R1164

Bard; used with Q672L1185.

Y594R1243

R1172

Heil Quaker; used with Q672L1193.

Y594R1243

R1180

York; Celsius; used with Q672L1011.

Y594R1664

Y594R1664

R1198

TRADELINE; used with Q672L1227

Y594R1243

R1206

For use with W89; used with Q672L1235.

None

R1214

Intertherm logo; used with Q672L1276.

Y594R1300

R1222

York logo; used with C815A1039; adjustable
anticipator stage-2 heat; used with Q672L1284

Y594R1672

R1230

Amana logo; no. C62397-1; used with
Q672L1300, W89.

None

R1255

Singer logo; used with Q672L1326 and W89.

None

R1271

Westinghouse logo; used with Q672L1375 and
W89.

Y594R1664

R1297

York; Celsius scale; used with Q672L1011.

None

R1305

Used with Q672L1235 and W89.

None

R1321

Duotherm logo; used with Q672L1409, and W89.

None

Williamson; used with Q672L1391.

Y594R1243

R1339
T872S
S1005

T872T
T1004
T872W

a

T874 Trade
Replacementa

Description

Wiring differences (old=new): B=X,
W=W2.

Wiring differences (old=new):
W1=B, Z=L, K=E.

Heat pump model; 2-stage heat plus changeover,
1-stage cool.
Westinghouse logo; adjustable anticipator stage 1 T874C1018/
Q674C1058
and 2 heat; fixed anticipator stage 1 heat;
changeover with heating: used with Q672C1045

Wiring differences (old=new):
V=RC-RH, F=G, C=Y1, Z=B,
H2=W2; W1-Y1 jumper required.

1-heat stage, 1-vent and 2-cool stages.
Trane logo; used with Q672B1129.

None

3-heat stages, 2-cool stages, manual changeover

W1019

Lennox logo; no. 52C7501; used with Q672L1342 None
and C815A1013.

W1027

Westinghouse logo; used with Q672L1268 and
C815A1021.

None

W1035

TRADELINE; used with C815A1043 and
Q672B1251.

Y594W1014

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and the subbase.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number
Q672A

Q674 Trade
Replacementa

Description
System: HEAT-AUTO-COOL, Fan: AUTO-ON

A1005

Standard OEM

A1013

TRADELINE

Q674A1019

A1021

RC-RH jumper

Q674A1019

RC-RH jumper required.

A1039

RC-RH jumper; Chek Lite

Q674A1019

RC-RH jumper required.

Q672B

Q674A1019

System: HEAT-OFF-COOL, Fan: AUTO-ON

B1004

Standard OEM

Q674B1034

B1012

Isolated G terminal.

Q674B1018

B1020

System: HEAT-OFF-RESET-COOL

Q674B1034

B1038

TRADELINE

Q674B1034

B1046

Heat pump circuit; used with T872R1008.

Y594R1425

Wiring differences (old=new):
W1=Y1, W=W2.

B1053

RC-RH jumper

Q674B1034

RC-RH jumper required.

B1061

Chek Lite

Q674B1034

Used system off as reset position.

B1079

Auto fan operation in heat and cool.

Q674B1075

B1087

Carrier no. HH93AZ078; RC-RH jumper.

Q674B1075

B1095

Carrier no. HH93AZ084; RC-RH jumper.

Q674B1034

B1103

Addison; heat pump circuit; used with
T872R1016.

Y594R1425

B1111

Carrier no. HH93AZ080; isolated G terminal.

Q674B1018

B1129

Trane special circuit; used with T872T1004.

None

B1137

RC-RH jumper; isolated G terminal.

Q674B1018

RC-RH jumper required.
RC-RH jumper required.

Wiring differences (old=new):
W=W2; W1-Y1 jumper required.

B1145

Fedders special

Q674B1034

B1152

Fedders special; auto fan operation in heat
and cool.

Q674B1075

B1160

Lennox; heat pump circuit; used with
T872R1024; includes compressor lockout in
EM. HT.

Y594R1243

B1178

General Electric no. AY28X107; auto fan
operation in heat and cool.

Q674B1075

B1186

Trane; isolated G terminal; Filter LED.

Q674B1018

B1194

General Electric no. AY28X124; auto fan
operation in heat and cool.

Q674B1075

Set T874 stage-1 anticipator for
combined load of heat relay and fan
relay.

B1202

Lennox no. P-8-11223; heat pump circuit; used
with T872R1040.

Y594R1243

Wiring differences (old=new):
V-VR=R, M=Y, Y=W2, F=G, R=O.

B1228

General Electric no. BAY28X137; isolated
G terminal.

Q674B1018

B1236

Carrier no. HH-93AZ079; RC-RH jumper;
LOCKOUT LED indicates compressor lockout
switch activated.

Q674B1034

RC-RH jumper; LED cannot be
provided in TRADELINE model.

B1244

Friedrich; heat mode changeover; used with
T872R1115.

T874C1018/
Q674B1034

Wiring differences (old=new): C=no
connection; RC-RH and W1-Y1
jumpers required.

B1251

Used with T872W1035 and C815A1043.

Y594W1014

B1210

a

Remarks

Wiring differences (old=new):
V-VR=R, M=Y, Y=W2, F=G, R=O.

None

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

39

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number

Q674 Trade
Replacementa

Description

B1269

Whalen; Hi-Lo fan switch; constant fan in heat
and cool system switch positions; used with
T872C1574.

None

B1277

Square D no. HCB-5.

Q674B1034

B1285

Wards; RC-RH and F-W3 jumpers; used with
T872C1673.

Gas Furnace:
T874C1018/
Q674B1034
Electric Furnace:
T874C1018/
Q674B1075

B1293
Q672C
C1003

Adjust anticipator faster for correct
performance.

Same as
Q672B1285

System: OFF-AUTO, Fan: AUTO-ON
Standard OEM

Q674C1058

C1011

Westinghouse; RC-RH jumper.

Q674C1058

RC-RH jumper required.

C1029

W1-Y2 jumper; for heat pump; used with
T872D1136.

Q674E1049

Replacement has heat/cool system
switching.

C1037

Chrysler Airtemp; System: COOL-OFF-AUTO.

Q674C1058

C1045

Westinghouse; heat pump; used with
T872S1005.

T874C1018/
Q674C1058

Wiring differences (old=new):
V=RC-RH, F=G, C=Y1, Z=B,
H2=W2; W1-Y1 jumper required.

C1052

Isolated stage 2 heat circuit for dc electric heat
relay.

Recontrol

Use T874G1246/Q674F1212 which
adds HEAT-COOL-EM.HT. system
switch.

C1060

Fedders special.

Q674C1058

C1078

General Electric no. AY28X109.

Q674C1058

C1086

Command-Aire; heat pump; used with
T872H1009.

Y594H1012

TRADELINE

Q674C1058

C1102
Q672D

System: None. Fan: None.

D1002

Standard OEM; used with T872F1126.

Q674D1040

D1010

Lennox special.

None

D1028

Carrier; RC-RH jumper.

None

D1036

Carrier no. HH93AZ070; RC-RH jumper.

Q674D1040

D1044

General Electric no. AY-28X100.

None

D1069

Square D no. HCB-4.

None

D1077

York; used with T872G1364.

None

D1085

TRADELINE

Q674D1040

Q672E

a

Lennox no. 41C96; used with T872C1673.

Remarks

RC-RH jumper required.

System: OFF-HEAT-AUTO-COOL
Fan: AUTO-ON

E1001

Standard OEM

Q674E1049

E1019

Lennox no. P-8-8892; heat pump; cool mode
changeover; used with T872G1026.

T874D1165/
Q674B1075

E1027

Heat pump circuit; W1-Y2 jumper; cool mode
changeover; used with T872G1018.

Y594G1393

Wiring differences (old=new): Y1=O,
Y2=Y.

E1035

Heat pump circuit; W1-Y2 jumper; cool mode
changeover.

Y594G1393

Wiring differences (old=new): Y1=O,
Y2=Y.

E1043

Heat pump circuit; heat mode changeover.

Q674E1049

Wiring differences (old=new):
W1=B, W2=W1; W1-Y1 jumper.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

60-2485—8

40

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number

Remarks

E1050

TRADELINE

Q674E1049

E1068

RC-RH jumper; used with T872C1699.

Q674E1049

RC-RH jumper required.

E1076

RC-RH internal jumper; EM. HT. LED.

Q674E1049

RC-RH jumper required.

E1084

Carrier no. HH93AZ076; RC-RH jumper.

Q674E1049

RC-RH jumper required.

E1092

Carrier no. HH93AZ082; RC-RH jumper; B
terminal; isolated G terminal.

Q674E1049

E1100

General Electric no. AY28X099.

Q674E1049

E1118

Airtemp; heat pump; used with T872D1169.

T874D1165/
Q674E1049

Wiring differences (old=new):
A=W1; set H1 anticipator to 1.2A.

E1126

Common R terminal.

Q674E1049

RC-RH jumper required.

E1134

ITT Nesbitt; RC-RH jumper; O and B terminals; Q674E1049
isolated G terminal.

E1142

Lennox no. P-8-11224; heat pump;
Y594G1252
V-VR jumper; cool mode changeover; used with
T872G1067.

Wiring differences (old=new):
V-VR=R, Y=W2, R=O, M=Y, F=G.

E1159

Carrier no. HH93AZ077; RC-RH jumper;
LOCKOUT LED indicates activation of
compressor lockout switch.

RC-RH jumper required; no LED in
TRADELINE model.

Q674E1049

E1167

Square D no. HCB-2; Chek Lite.

Q674E1049

E1183

Square D no. HCB-3.

Q674E1049

E1191

Lennox; HIGH and LOW LEDs; used with
T872D1045.

Q674E1049

No LEDs on replacement.

Q672F

a

Q674 Trade
Replacementa

Description

System: EM. HT.-HEAT-AUTO-COOL-OFF
Fan: AUTO-ON.

F1000

With EM. HT. LED; used with T872C1699.

Q674F1022

Remove W3-X2 jumper to E-X2.

F1018

Heat pump; heat mode changeover; Chek Lite;
used with T872G1000.

Y594G1252

Wiring differences (old=new):
W=W2, X1=X.

F1026

Chek Lite; W2-X2 jumper.

Q674F1022

F1034

Airtemp; EM. HT. LED; RC-RH and X2-E
jumpers.

Q674F1022

F1042

W2-X2 jumper; Chek Lite.

Q674F1022

F1059

Carrier no. HH93AZ074; EM. HT. LED.

Q674F1022

F1067

Lennox; heat pump; cool mode changeover;
EM. HT. LED; used with T872G1026.

None

F1075

Heat pump circuit; EM. HT. LED; 2 terminal; RC- None
RH jumper.

F1083

Lennox no. P-8-11225; heat pump;
V-VR jumper; cool mode changeover; EM. HT.
LED; used with T872G1067.

None

F1091

Westinghouse; heat pump; EM. HT. LED; cool
mode changeover; compressor lockout in
EM. HT.; used with T872G1034.

Y594G1252

Wiring differences (old=new):
W=W2.

F1109

Airtemp no. 3778567ACC; R-X2 jumper;
EM. HT. LED.

Q674F1022

R-X2 jumper required.

F1117

Tappan no. 080-13708-53; heat pump; EM. HT. Y594G1252
LED; cool mode changeover; compressor
lockout and auto fan in EM. HT.; used with
T872G1109, G1216, G1372.

If RC-RH jumper removed on
Q672F1034, Q674F1022 does not
replace.
Remove W2-X2 jumper to E-X2; X
terminal same as C.

Wiring differences (old=new): C=X.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

41

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number
F1125

BDP no. 3442DP90; used with T872G1117,
G1166, G1174.

Y594G1252

F1133

Williamson; heat pump; EM. HT. LED; heat
mode changeover; compressor lockout in
EM. HT.; used with T872N1010.

T874N1016/
Q674F1220

F1141

Westinghouse; EM. HT. LED; auto fan in
EM. HT.; used with T872G1034.

Y594G1252

F1158

Rheem Ruud; heat pump; EM. HT. LED; cool
Y594G1252
mode changeover; compressor lockout in
EM. HT.; used with T872G1083, G1133, G1141;
auto fan in EM. HT.

F1166

Crispaire; EM. HT. LED; used with T872G1208. Y594G1252

F1174

Carrier no. HH93AZ081; EM. HT. LED.

Q674F1022

F1182

Square D no. HCB-1; Chek Lite; R-X2 jumper;
System: Aux. Heat replaces EM. HT.

Q674F1022

F1190

EM. HT. LED; X2-E and RC-RH jumpers.

None

F1208

TRADELINE; cool mode changeover; EM. HT.
LED; used with T872G1224.

Y594G1419

F1216

TRADELINE; heat mode changeover; EM. HT.
LED; used with T872N1028.

T874N1016/
Q674F1220

F1224

Heatwave (Southwest Mfg.); compressor
lockout in EM. HT.; EM. HT. LED; used with
T872G1232.

Y594G1252

F1232

Rheem; cool mode changeover; EM. HT. and
AUX. HEAT LEDs; compressor lockout in
EM. HT.; used with T872G1133.

Y594G1252

F1240

Lennox; cool mode changeover; EM. HT. and
SERVICE LEDs; used with T872G1240.

None

F1257

Westinghouse; cool mode changeover;
EM. HT. and AUX. HEAT LEDs; auto fan in
EM. HT; used with T872G1034.

Y594G1252

F1265

Wesco Addison; Chek and EM. HT. LEDs; used Y594G1252
with T872G1281, G1265.

F1273

Southwest special; no. 0361-136; W2-X2
jumper.

None

F1281

Luxaire special; used with T872G1315.

Y594G1252

F1299

Bard special; used with T872N1036, N1044.

T874N1016/
Q674F1220

F1315

Williamson special; used with T872N1010.

T874N1016/
Q674F1220

Crispaire special; used with T872G1208.

Y594G1252

F1323
Q672G

a

Q674 Trade
Replacementa

Description

Remarks
Wiring differences (old=new): C=X.

Wiring differences (old=new):
W=W2.

R-X2 jumper; add monitor switch
between X1 and low side of power.

Wiring differences (old=new):
W=W2.
Wiring differences (old=new): C=X.

System: OFF-AUTO. Fan: None.

G1009

Standard OEM

Q674G1070

G1017

Singer; O-B jumper; used with T872D1375.

Q674G1070

G1025

Includes O and B terminals.

Q674G1070

G1033

General Electric no. AY28X102.

Q674G1070

G1041

Singer no. 02005649; French wording; O-B
jumper.

Q674G1070

Less French wording.

G1066

SLI-Mammoth; heat pump; heat mode
changeover.

Q674G1070

Connect fan (G) wire to Y1 terminal;
B-O and RC-RH jumpers.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

60-2485—8

42

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number
G1074

Singer no. 02005754; X1 and X2 terminals for
field-added indicator lights; used with
T872D1375.

None

G1082

Singer no. 02005792; X1 and X2 terminals for
field-added indicator lights; used with
T872D1375.

None

G1090

TRADELINE; B and O terminals.

Q674G1070

Q672H
H1008
Q672J

Used with T872.

None

System: EM. HT.-AUTO-OFF
Fan: AUTO-ON.
With EM. HT. LED; used with T872C or D.

None

J1013

Westinghouse; heat pump; EM. HT. LED; cool
mode changeover; compressor lockout in
EM. HT.; used with T872G1034.

Y594G1252

J1021

York; heat pump; EM. HT. LED; cool mode
Y594G1567
changeover; compressor lockout and auto fan in
EM. HT.; E-W jumper; used with T872G1042,
G1331, G1398.

J1039

Y594G1161
Heat pump; EM. HT. and AUX. HEAT LEDs;
cool mode changeover; compressor lockout and
auto fan in EM. HT.; used with T872G1059.

J1047

Singer no. 02005699; heat pump; EM. HT. LED; Q674F1022
heat mode changeover.

J1054

Carrier no. HH93AZ073A; heat pump; EM. HT.
LED; cool mode changeover; compressor
lockout in EM. HT.; used with T872G1075,
G1182, G1307.

J1062

Westinghouse; EM. HT. and AUX. HEAT LEDs; Y594G1252
used with T872G1034.

Y594G1252

Designed for use on General
Electric heat pumps.

Wiring differences (old=new): C=X.

Wiring differences (old=new):
W=W2.

System: OFF-HEAT-AUTO-COOL. Fan: None.

K1004

Carrier no. HH93AZ072.

K1012

Oneida Heater no. 30A0288-01; System: OFF- T874F1155/
WOOD-WOOD/OIL-OIL; used with T872F1175. Q674K1026

Q672L

Remarks

System: OFF-ON
Fan: NIGHT INT.-DAY CONT.

J1005

Q672K

a

Q674 Trade
Replacementa

Description

Q674E1049

Fan switch does not function.

System: EM. HT.-HEAT-OFF-COOL.
Fan: ON-AUTO.
Y594R1425

L1003

Lennox; heat pump; EM. HT. LED; cool mode
changeover; used with T872R1024.

L1011

Y594R1664
York; heat pump; EM. HT. LED; cool mode
changeover; compressor lockout and auto fan in
EM. HT.; used with T872R1032, R1180, R1297.

L1029

Lennox no. P-8-11226; heat pump; EM. HT.
LED; V-VR jumper; cool mode changeover;
compressor lockout in EM. HT.; used with
T872R1040.

L1037

Heat pump; EM. HT. and AUX. HT. LEDs; cool Y594R1763
mode changeover; compressor lockout and auto
fan in EM. HT.; used with T872R1057.

L1045

Rheem; heat pump; EM. HT. LED; cool mode
changeover; compressor lockout in EM. HT.;
auto fan in EM. HT; used with T872R1065,
R1081, R1107.

Y594R1425

Wiring differences (old=new):
V-VR=R, M=Y, Y=W2, F=G, R=O.

Wiring differences (old=new): A=T;
designed for used on General
Electric heat pumps.

Y594R1243

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

43

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number

a

Q674 Trade
Replacementa

Description

Remarks

L1052

Carrier no. HH93AZ075; heat pump; EM. HT.
LED; cool mode changeover; compressor
lockout in EM. HT.; used with T872G1075,
G1182, G1273, G1307.

Y594R1615

L1060

Dunham Bush; EM. HT. LED; used with
T872R1099.

Y594R1243

L1078

Tappan no. B13708-58; heat pump; EM. HT.
LED; cool mode changeover; compressor
lockout in EM. HT.; EM. HT. relay provides fan
operation in EM. HT.; used with T872G1190.

None

L1086

Friedrich; heat mode changeover; EM. HT. LED; Y594R1243
used T872R1115 with L terminal.

Wiring differences (old=new): X2=E,
C=X.

L1094

Crispaire; W2-H jumper; EM. HT. LED; used
with T872R1065, R1156.

Replacement has auto fan in
Emergency Heat mode.

L1102

Fedders; heat mode changeover; EM. HT. LED; Y594R1425
used with T872C1509, C1517, C1541.

Wiring differences (old=new): K=E,
C=X; remove Y-W1 jumper.

L1110

Westinghouse; EM. HT. LED; used with
T872R1149.

Y594R1243

Wiring differences (old=new):
W=W2.

L1128

Westinghouse; EM. HT. LED; used with
T872R1149.

Y594R1243

Wiring differences (old=new):
W=W2.

L1136

Y594R1243
Rheem no. 41-20796-07; cool mode
changeover; EM. HT. and AUX. HT. LEDs; used
with T872R1081, T872R1107.

L1144

Lennox; V-VR jumper; EM. HT. and SERVICE
LEDs; isolated stage 2 heat; used with
T872R1131, C815A1013.

None

L1151

Westinghouse; AUX. HT. and EM. HT. LEDs;
used with T872R1149.

Y594R1243

L1169

Carrier no. HH93AZ071; EM. HT. LED; used
with T872G1257 (HH07AT073).

None

L1177

York; DoD; EM. HT. LED; used with T872G1299. Y594G1567

L1185

Bard; used with T872R1164.

Y594R1243

L1193

Heil Quaker no. NAXA001TS01; used with
T872R1172.

Y594R1243

L1201

Lennox special; no. 1485701; used with
T872G1323.

None

L1219

Westinghouse special; used with T872G1356.

T874D1165/
Q674F1022

L1227

Heat pump; used with T872R1198.

Y594R1243

L1235

Intertherm; used with T872R1206, R1305.

None

L1250

Crispaire special; used with T872R1156 and
C815A1021.

Y594R1243

L1268

Westinghouse special; used with T872W1027
and C815A1021.

None

L1276

Intertherm special; used with T872R1214.

Y594R1300

L1284

York special; used with T872R1222.

Y594R1672

L1300

Amana special; no. C62345-1; used with
T872R1230.

None

L1326

Singer; used with T872R1255.

None

Y594R1243

Wiring differences (old=new): C=X.

Wiring differences (old=new):
W=W2.

Wiring differences (old=new): B=X,
W=W2.

Wiring differences (old=new): X=X1,
L=X2, W=E; Y1-W1 and
Y2-W2 jumpers required.

Wiring differences (old=new):
W1=B, Z=L, K=E.

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

60-2485—8

44

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 7. Q672-Q674 Subbase Cross Reference.
Model Number
L1342

Lennox no. 52C7601; used with T872W1019
and C815A1013.

None

L1375

Westinghouse; used with T872R1271, W89.

None

L1383

Dunham Bush; used with T872R1099.

Y594R1243

L1391

Williamson; used with T872R1339.

Y594R1243

L1409

Duotherm special; used with T872R1321, W89. None

Q672N

Goettl; heat pump; heat mode changeover;
evaporative cooler circuit; Fan: AUTO-ON;
System: AUTO; used with T872C1459.

None

N1019

Goettl; heat pump; heat mode changeover;
evaporative cooler circuit; W1-Y1 jumper; used
with T872C1459.

None

N1027

Siegler special; used with T872C1707.

None

P1009

Remarks

System: OFF-HEAT-COOL-EVAP.

N1001

Q672P

a

Q674 Trade
Replacementa

Description

System: EM. HT.-HEAT-COOL.
Carrier special; no. HH93AZ069; used with
T872G1075 (HH07AT071).

Y594R1243

Replacement has OFF system
switch position

When replacing a T872 Thermostat and Q672 Subbase, always replace both the thermostat and subbase.

45

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

T874A

Trade Model
Replacement

Description

Remarks

1-stage heat, 1-stage cool.
44, 65 Honeywell logo; Standard OEM; used with Q674B1331.

T874A1036

44

Honeywell logo; includes Allen wrench and screws to
lock cover; non-adjustable range stops set at 72°F (max.
heat) and 78°F (min. cool) (22-26°C); field adjustable
locking levers.

T874A1010

A1028

44

Honeywell logo; heat anticipator factory set at 0.4A.

T874A1036

A1036

44

Honeywell logo; TRADELINE® model; includes Allen
wrench and screws to lock cover; field adjustable
locking levers.

T874A1036

A1044

44

Obsolete. AAF/Snyder General logo; part no. 4ELN3006C; °F/°C scaleplate.

T874A1036

Replacement has °F
scaleplate.

A1051

44

Lennox logo; part no. 12F9901; °F/°C scaleplate; heat
anticipator set at 0.45A.

T874A1036

Replacement has °F
scaleplate.

A1069

44

Obsolete. Westinghouse logo; used with Q674A-E,G.

T874A1036

A1002
A1010

A1077

46, 82 Obsolete. Amana Air Conditioning logo; part no.
D68535-1; heat anticipator factory set at 1.2A; used with
Q674B1075, E1056; used in Y594A1001, A1019.

T874A1036

A1085

44, 46, Obsolete. Trane logo; part no. 13510451; used with
55, 66 Q674B1018, B1075, D1008.

T874A1036

A1093
A1101

44

Obsolete. McQuay logo; part no. 02005935; °F/°C
scaleplate.

51, 53 Carrier logo; part no. HH07AT174; used with Q674B.

T874A1036

Replacement has °F/°C
scaleplate.

Y594C1421 or When using the T874C1036,
T874A1036a set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary.

A1119

82

Obsolete. Sears logo; part no. 541. 91441/49. 9144; °F/
°C scaleplate; used with Q674E1007; used in
Y594A1068.

T874A1036

Replacement has °F
scaleplate.

A1127

44

Obsolete. Climate Control logo; part no. 02005936; °C
scaleplate.

T874A1036

Replacement has °F
scaleplate.

A1135

44

Fedders multi-logo; part no. THTX-110-WCHA,
88-58-00500-001.

T874A1036

A1143

44

Honeywell logo; °C scaleplate.

T874A1036

A1150

44

Honeywell logo; TRADELINE model; includes Allen
wrench and screws to lock cover; field adjustable
locking levers (68°F max. heat, 78°F min. cool).

T874A1150

A1168

44

Obsolete. Trane Comfort Corps logo.

T874A1036

A1176

44

Honeywell logo; meets DoD specs; includes Allen
wrench and screws to lock cover; no thermometer; nonadjustable range stops set at 72°F (max. heat) and 78°F
(min. cool) (22-26°C); field adjustable locking levers.

T874A1176

A1184

A1192

51, 53 Trane logo; part no. BAY28X182; °F/°C scaleplate;
automatic fan in heating and cooling modes; heat
anticipator set at 0.4A; used with Q674B1141, E1080.

44

Obsolete. Lennox logo; part no. 13F0001; °C scaleplate;
heat anticipator factory set at .458A.

a

Both the thermostat and subbase must be replaced.

60-2485—8

46

Replacement has °F
scaleplate.

T874A1036a

When used with Q674E1080,
set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary;
replacement has °F
scaleplate.

T874A1036

Replacement has °F
scaleplate.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number
A1200

Fig.
No.

Trade Model
Replacement

Description

51, 53 Obsolete. Carrier logo; part no. HH07AT164; °C
scaleplate; includes Allen wrench and screws to lock
cover; used with Q674B.

Remarks

T874A1036

Set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary;
replacement has °F
scaleplate.
Replacement has °F
scaleplate.

a

A1226

44

Honeywell logo; Honeywell Canada TRADELINE model;
°C scaleplate; includes Allen wrench and screws to lock
cover.

T874A1036

A1234

44

Obsolete. Friedrich Climate Master logo; heat
anticipator factory set 1.2A.

T874A1036

A1242

44

Obsolete. Friedrich Climate Master logo.

T874A1036

A1259

44

Obsolete. Wesco logo; heat anticipator set at 0.8A.

T874A1036

A1267

59

Obsolete. McQuay logo; used with Q674Q1004.

T874A1036

A1275

44

Obsolete. Lennox logo; part no. 13F0101; meets DoD
specifications.

T874A1176

A1283

75

McQuay Air Conditioning logo; part no. 03005047; used
with Q674C1132 and thermistor to display outdoor
temperature.

T874A1036

Replacement does not have
ability to display external
temperature or momentary
system switch position.

A1291

64

No logo; three-speed fan; one setpoint lever for heat and
cool setpoints; used with Q674Q1012; used in
Y594A1126.

T874A1036/
Q674B1075a

Replacement has two levers
and 1 speed fan.

A1309

44

Obsolete. Arcoaire Air Conditioning and Heating logo;
part no. AO2076; includes Allen wrench and screws to
lock cover.

T874A1036

A1317

44

Obsolete. McQuay logo; part no. 60685301; no
scaleplate; used with Q674A-E,G.

T874A1036

A1325

75

Obsolete. McQuay logo; part no. 60685401; no
scaleplate; used with Q674C1306 and outdoor
thermistor to display outdoor temperature.

T874A1036

A1341

44

Obsolete. Trane logo; part no. THT-0577; meets DoD
specifications.

T874A1176

A1358

44

York-Miraco logo.

T874A1036

A1366

51, 53 Obsolete. BDP Multi-logo; part no. HH07AT182.

T874A1036a

Replacement does not have
ability to display external
temperature or momentary
system switch position.

Set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary.

A1374

44

American Standard logo; part no. ASYSTAT610; heat
anticipator factory set at 0.4A.

T874A1036a

A1390

44

Obsolete. Climate Control logo; part no. 654958804; °F/
°C scaleplate.

T874A1036

Replacement has °F
scaleplate.

A1416

44

Obsolete. Reznor logo; part no. 654758803; °F/°C
scaleplate.

T874A1036

Replacement has °F
scaleplate.

A1424

214

Obsolete. Carrier Olympia Series Split System logo; part
no. HH07AT194; used with Q674B1455 (HH93AZ208).

A1440

91

Obsolete. Simplex System 2000 logo; heat anticipator
factory set at 1.2A; used with Q674G1005; used in
Y594A.

T874A1036

A1465

212

Honeywell Trol-A-Temp™ logo; Premier White® color;
heat anticipator factory set at 0.10A; used with
Q674E1379.

None

See OEM for
replacement.

See Trol-A-Temp for
replacement.

a

Both the thermostat and subbase must be replaced.

47

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

A1481

44

Obsolete. Honeywell logo; Carrier part no. HH621602;
includes locking cover and non-adjustable range stops
set at 72°F (max. heat) and 78°F (min. cool).

T874A1036

A1507

44

Obsolete. Climate-Tel logo; includes Allen wrench and
screws to lock cover and non-adjustable range stops set
at 72°F (max. heat) and 78°F (min. cool).

T874A1176

A1523

224,
225

Obsolete. AAF/Snyder General logo; part no.
066804404; °F/°C scaleplate; no cooling anticipation;
used with Q674E1312, C1298.

See OEM for
replacement.

A1549

224,
225

Obsolete. McQuay logo; part no. 066816601; no cooling
anticipation; used with Q674E1312, C1298.

See OEM for
replacement.

A1556

Trade Model
Replacement

Description

51, 53 Carrier logo; part no. HH07AT164-W; °C scaleplate;
Premier White® color; includes Allen wrench and
screws to lock cover; used with Q674B.

T874A1036a

A1572

224,
225

Obsolete. McQuay logo; part no. 066816611; Premier
White® color; °F/°C scaleplate; no cooling anticipation.

See OEM for
replacement.

A1580

91

California Economizer logo; Premier White® color; heat
anticipator factory set at 1.2A.

T874A1036

A1598

224,
225

McQuay logo; part no. 073319001; Premier White®
color; °F/°C scaleplate; includes Allen wrench, screws to
lock cover and AAF insert.

See OEM for
replacement.

A1614

44

Honeywell logo; TRADELINE® model; °C scaleplate;
Premier White® color; includes Allen wrench and
screws to lock cover; used with Q674B.

T874A1036

A1622

44

Obsolete. York logo; part no. 2TH04703224A; includes
Allen wrench and screws to lock cover and nonadjustable range stops set at 72°F (max. heat) and 78°F
(min. cool).

T874A1010

B1001

44

Obsolete. Honeywell logo.

T874B1019

B1019

44

Honeywell logo; TRADELINE model; includes Allen
wrench and screws to lock cover.

T874B1019

44

Obsolete. Westinghouse logo.

T874B1019

B1035

Replacement has °F
scaleplate; replacement is
beige.

Replacement has °F
scaleplate; replacement is
beige.

1-stage heat, 2-stage cool.

T874B

B1027

Remarks

44, 46 Obsolete. Trane logo; used with Q674B1018, B1075;
used in Y594B1026, B1034.

T874B1019

B1043

44

Obsolete. Honeywell logo; °C scaleplate.

T874B1019

Replacement has °F
scaleplate.

B1050

44

Lennox logo; part no. 13F0201; °F/°C scaleplate.

T874B1019

Replacement has °F
scaleplate.

B1068

44

Honeywell logo; Honeywell Canada TRADELINE model;
°C scaleplate; includes Allen wrench and screws to lock
cover.

T874B1019

Replacement has °F
scaleplate.

B1076

88

Obsolete. Lennox Power Saver Two-Speed logo; part
no. 91C7401; °F/°C scaleplate; used with Q674E1155.

T874B1019

Replacement has °F
scaleplate.

B1084

44

Obsolete. Lennox Two-Speed logo; part no. 13F0301;
°C scaleplate.

T874B1019

Replacement has °F
scaleplate.

B1092

44

Obsolete. Honeywell logo; Heil Quaker part no.
HQ521389HW.

T874B1019

B1100

88

Obsolete. Janitrol logo; part no. CHTS36-60; °F/°C
scaleplate; used with Q674E1338; used in Y594B1042.

T874B1019

Replacement has °F
scaleplate.

B1118

44

Honeywell logo; °C scaleplate; used with
Q674A-E, G.

T874B1019

Replacement has °F
scaleplate.

a

Both the thermostat and subbase must be replaced.

60-2485—8

48

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

B1134

222

T874C

Trade Model
Replacement

Description
Obsolete. Carrier Synergy 2000 logo; part no.
HH07AT199; °C scaleplate; used with Q674E1395
(HH93AZ209).

T874B1019/
Q674E1049a

Remarks
Wiring differences (old=new):
W1=W; RC-RH jumper
required; replacement has no
LEDs.

2-stage heat, 1-stage cool.

C1000

44, 76 Honeywell logo; used with Q674B1075, C1181; used in
Y594C1058.

T874C1018

C1018

60, 61, Honeywell logo; TRADELINE model; includes Allen
81, 92 wrench and screws to lock cover; used with
Q674C1074.

T874C1018

C1026

44

Obsolete. AAF logo; °C scaleplate; includes Allen
wrench and screws to lock cover; non-adjustable range
stops set at 23°C (max. heat and min. cool) (73°F).

T874C1018

Replacement has °F
scaleplate.

C1034

44

Lennox logo; part no. 13F0401; °F/°C scaleplate.

T874C1018

Replacement has °F
scaleplate.

C1042

44

Obsolete. Westinghouse logo; H1 anticipator factory set
at.75A; H2 anticipator factory set at 1.2A; used with
Q674A-E,G.

T874C1018

C1059

C1067
C1075

44, 142 Obsolete. Amana Air Conditioning logo; part no.
D68535-2; H1 anticipator factory set at 1.2A; used with
Q674E1056, Q674B1059, Q674F1022; used in
Y594C1009, Y594C1017, Y594C1256, Y594C1330.

T874C1018

Obsolete. Sears logo; part no. 42. 9297; °F/°C
scaleplate.

T874C1018

44

51, 53 Carrier logo; part no. HH07AT170; used with
Q674B1166.

Y594C1421 or When using the T874C1018,
T874C1018a set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary.

C1083

44

Obsolete. Trane logo; used with Q674E1007; used in
Y594C1082.

T874C1018

C1117

44

Honeywell logo; °C scaleplate.

T874C1018

C1125

60, 61, Obsolete. Honeywell logo; 12°F (6.7°C) differential
between stage 1 heat and stage 2 heat; used with
92
Q674G1047.
96

Obsolete. AAF/Snyder General logo; part no.
4ELN7546; no H1 heat anticipation; used with Q674AG,N and Q674C1173.

T874C1018

C1141

44

Obsolete. Honeywell logo; meets DoD specs; includes
Allen wrench and screws to lock cover; no thermometer;
non-adjustable range stops set at 72°F (max. heat) and
78°F (min. cool) (22-26°C); field adjustable locking
levers.

T874C1141

C1158

44

Obsolete. Solaron special.

T874C1018

51, 53 Obsolete. Carrier logo; part no. HH07AT160; °C
scaleplate; includes Allen wrench and screws to lock
cover; used with Q674B.

Replacement has °F
scaleplate.

T8611M2025

C1133

C1166

Replacement has °F
scaleplate.

T874C1018a

C1174

44

Obsolete. Goettl logo.

T874C1018

C1182

60

Obsolete. Goettl logo; H1 anticipator factory set at 0.8A;
used with Q674N1015.

T874C1018

C1190

44

Obsolete. Lennox logo; part no. 13F0501; °C scaleplate.

T874C1018

Must have H1 anticipator set
to maximum value.

Replacement has °F
scaleplate; set stage 1 heat
anticipator for total current
draw of fan and stage 1 heat
primary.

Replacement has °F
scaleplate.

a

Both the thermostat and subbase must be replaced.
49

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

Description

Remarks

C1216

44

Obsolete. Fasco part no. 1230-8197.

T874C1018

C1224

105

Obsolete. Square D logo.

T874C1018

C1240

44

Honeywell logo; Honeywell Canada TRADELINE model;
°C scaleplate; includes Allen wrench and screws to lock
cover.

T874C1018

Replacement has °F
scaleplate.

C1257

44

Obsolete. Singer part no. 0200-5931; 8°F (4.4°C)
differential between H1 and H2 heat.

T874C1125

Replacement has 12°F
differential between H1 and
H2 heat.

C1265

44

Obsolete. Singer special; °C scaleplate; 5°C (8°F)
differential between H1 and H2 heat.

T874C1125

Replacement has 12°F
differential between H1 and
H2 heat; replacement has °F
scaleplate.

C1273

44

Honeywell logo; °C scaleplate; includes Allen wrench
and screws to lock cover; non-adjustable range stops
factory set at 23°C (max. heat and min. cool) (73°F).

T874C1018

Replacement has °F
scaleplate.

C1281

44

Obsolete. Heat Wave special.

T874C1018

C1307

44

Obsolete. Friedrich Climate Master logo.

T874C1018

C1315

44

Obsolete. Wesco logo; heat anticipator factory set at
0.8A.

T874C1018

C1323

44

Obsolete. Le Chauffage Urbain special; °C scaleplate.

T874C1018

82, 141 Obsolete. Duotherm logo; used with Q674E or Q674F.

T874C1018

C1331

Replacement has °F
scaleplate.

C1349

61

Obsolete. Sigler logo; used with Q674N1023.

T874C1018

C1372

52

Obsolete. Honeywell logo; used with Q674B1190.

T874C1018/
Q674B1034

For systems requiring
automatic fan in cooling mode
only.

T874C1018/
Q674B1075

For systems requiring
automatic fan in heating and
cooling.

C1398

105

Obsolete. Fedders logo; °F/°C scaleplate; used with
Q674L1090.

Y594R1425a

Wiring differences (old=new):
K=E, C=X; replacement has °F
scaleplate.

C1406

105

Obsolete. Climatrol logo; °F/°C scaleplate; used with
Q674L1090.

Y594R1425a

Wiring differences (old=new):
K=E, C=X; replacement has °F
scaleplate.

C1414

105

Obsolete. Airtemp logo; °F/°C scaleplate; used with
Q674L1090.

Y594R1425a

Wiring differences (old=new):
K=E, C=X; replacement has °F
scaleplate.

C1422

187

Obsolete. Honeywell logo; used with Q674B1208.

C1430

49

Obsolete. Lennox Zone Master Two-Speed logo; part
no. 25F7201; used with Q674B1224.

T874C1018

C1448

110,
190

Obsolete. Lennox logo; part no. 24F5101; meets DoD
specifications; requires outdoor reset; used with
Q674L1165, L1355.

Y594R1763a

C1455

127

Obsolete. Williamson logo; used with Q674L1322.

Y594R1243a

C1463

82

Obsolete. AAF logo; °C scaleplate.

T874C1018

C1471

56

Obsolete. Mammoth logo; part no. 71120102; used with
Q674B1257; used in Y594C1314.

T874C1018

a

Both the thermostat and subbase must be replaced.

60-2485—8

50

None

Wiring differences (new=old):
R=V-VR, Y=M, G=F, B-X,
W=Y, T=A, O=R, X2=E;
Emergency Heat becomes
stage 1 heat source.
Replacement has °F
scaleplate.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

C1489

121

Obsolete. Honeywell logo; non-adjustable range stops
set at 75°F (max. heat and min. cool) (24°C); used with
Q674L1157.

Y594C1322

C1497

121

Obsolete. Honeywell logo; meets DoD specifications;
used with Q674L1157.

Y594C1322a

C1513

44

Obsolete. Borg-Warner multi-logo; part no.
6TH11703124A.

T874C1018

C1562

44

Obsolete. Honeywell logo; Heil Quaker part no.
HQ712001HW.

T874C1018

C1570

45

Obsolete. Williamson logo; used with Q674B1000; used
in Y594C1280.

T874C1018

C1638

121

Obsolete. Honeywell logo; meets DoD specifications;
includes Allen wrench and screws to lock cover; no
thermometer; non-adjustable range stops set at 72°F
(max. heat) and 78°F (min. cool) (22-26°C); field
adjustable locking levers; used with Q674L1561; used in
Y594C1322.

Y594C1322a

C1653

70

Obsolete. Fiberglas Canada; °C scaleplate; no H1, H2,
or C1 anticipation; used with Q674S1000; used in
Y594C1348.

See OEM for
replacement.

C1661

99

Obsolete. McQuay logo; part no. 61202401; °F/°C
scaleplate; includes momentary system switch position
with spring release; used with Q674C1363.

T874C1125/
Q674B1075a

C1695

45

Obsolete. Miller logo; used with Q674B1000; used in
Y594C1355.

T874C1018

C1703

45

Obsolete. Intertherm logo; used with Q674B1000; used
in Y594C1363.

T874C1018

C1737

44

Obsolete. Honeywell logo; Carrier part no. HH621603.

T874C1018

C1745

44

Obsolete. AAF/Snyder General logo; part no.
4ELN7919.

T874C1018

C1752

219

Obsolete. McQuay/Snyder General logo; part no.
061202402; 12°F offset between H1 and H2; °F/°C
scaleplate; no C1 anticipation; used with Q674C1363.

T8611M2025

Description

Remarks

a

C1760

44

Bard logo.

T874C1018

C1778

219

Obsolete. AAF/Snyder General logo; part no.
066804405; 12°F offset between H1 and H2; °F/°C
scaleplate; no C1 anticipation; used with Q674C1363.

See OEM for
replacement.

C1794

53

Obsolete. Carrier logo; Canada; part no. HH07AT160-W;
Premier White® color; °C scaleplate; includes locking
cover.

T874C1018

C1802

246

Obsolete. California Economizer logo; °F/°C scaleplate;
used with Q674G1005; used in Y594C1371.

T874C1018

C1810

237

Obsolete. Honeywell logo; TRADELINE model; Premier
White® color; used with Q674B1547; used in
Y594C1389.

Y594C1389

C1844

238

Energy Night logo; used with Q674F1592; used in
Y594C1413.

Y594R1425

C1851

60

Obsolete. Whalen logo.

T874C1018

C1869

219

McQuay logo; part no. 0073318801 Premier White®
color; °F/°C scaleplate.

See OEM for
replacement.

Replacement has HEAT-OFFCOOL system switching; no
momentary system switch
position; no LEDs.

Set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary.

Jumper E-W2; system switch:
EM.HT.-HEAT-OFF-COOL.

a

Both the thermostat and subbase must be replaced.

51

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

C1877

53

T874D

Trade Model
Replacement

Description
Obsolete. Honeywell logo; TRADELINE model; used
with Q674B1554; used in Y594C1421.

Y594D1347

166, 82 Obsolete. Honeywell logo; used with Q674F1337,
E1007; used in Y594D1222, D1339.

T874D1165

D1017

44, 88 Obsolete. Honeywell logo; TRADELINE model; includes
Allen wrench and screws to lock cover; used with
Q674A-G and Q674E1155.

T874D1165

D1025

44

Obsolete. Westinghouse logo; H1 anticipator factory set
at 0.75A; H2 anticipator factory set at 1.2A.

T874D1165

D1033

44

Lennox logo; part no. 13F0601; °F/°C scaleplate.

T874D1165

D1041

53

York logo; part no. 2TH04701524A; used with
Q674B1125.

T874D1165

D1058

44

Obsolete. Shiger special.

T874D1165

44

Obsolete. ITT logo.

Replacement has °F
scaleplate.

T874D1165

D1074

51, 53, Carrier logo; part no. HH07AT172; used with
146 Q674F1030 (HH93AZ174), F1063 (HH93AZ181) or
Q674B.

T874D1165a

D1082

44, 46, Trane logo; used with Q674B1018, C1009, B1075,
48, 72 B1133; used in Y594D1024, D1040.

T874D1165

D1090

44

Obsolete. Dunham-Bush logo.

T874D1165

D1108

44

Obsolete. Westinghouse logo.

T874D1165

D1116

Jumper RC-RH; system
switch: OFF-HEAT-AUTOCOOL

2-stage heat, 2-stage cool.

D1009

D1066

Remarks

76, 89, Obsolete. Comfortmaker logo; part no. 1505-682; °F/°C
94
scaleplate; used with Q674C1116, E1197, G1104.

T874D1165

Set H1 anticipator for current
draw of fan and stage 1 heat
primary.

Replacement has °F
scaleplate.

D1124

44

Obsolete. Airtemp special.

T874D1165

D1132

44

Honeywell logo; °C scaleplate.

T874D1165

Replacement has °F
scaleplate.

D1140

44

Obsolete. Solaron special.

T874D1165

Replacement has °F
scaleplate.

T874D1165a

Replacement has °F
scaleplate; set H1 anticipator
for current draw of fan and
stage 1 heat primary.

D1157

51, 53, Carrier logo; part no. HH07AT172; °C scaleplate; used
146 with Q674B or Q674F1030, F1063.

Honeywell logo; SUPER TRADELINE® model; includes
Allen wrench and screws to lock cover, field-adjustable
range stops, field-adjustable locking levers.

T874D1165

D1173

51, 53 Trane logo; part no. BAY28X183; heat anticipator factory
set at 0.4A.

T874D1165a

Set H1 anticipator for current
draw of fan and stage 1 heat
primary.

D1181

51, 53 Obsolete. General Electric logo; locking cover includes
Allen wrench and screws to lock cover and range stops
set at 72°F (max. heat) and 78°F (min. cool).

T874D1165a

Set H1 anticipator for current
draw of fan and stage 1 heat
primary.

T874D1165

Replacement has °F
scaleplate.

D1165

82

D1199

44

Obsolete. Lennox logo; part no. 13F0701; °C scaleplate.

D1207

114

Obsolete. Lennox logo; part no. 24F5201; used with
Q674L1199 and C815A1013 or Q674L1389.

a

Both the thermostat and subbase must be replaced.

60-2485—8

52

T8611M2025 Wiring differences (old=new):
(programmable) V-VR=R, Y=W3, X=C, R=O,
M=Y, M2=Y2-W2, F=G;
jumper Y2-W2; no outdoor
reset needed; use only one
system transformer.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

D1215

44

Obsolete. Friedrich Climate Master logo; part no.
AT5415; °F/°C scaleplate.

T874D1165

Replacement has °F
scaleplate.

D1223

44

Honeywell logo; Honeywell Canada TRADELINE model;
Celsius scale.

T874D1165

Replacement has °F
scaleplate.

D1231

44

Obsolete. Honeywell logo; 12°F (7°C) differential
between H1 and H2.

T874D1165

Replacement has 2°F
differential between H1 and
H2.

D1249

44

Obsolete. Fedders special.

T874D1165

D1256

44

Obsolete. Climatrol special.

D1264

107

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT173; used with Q674L1116 (HH93AZ171).

D1272

D1280

Trade Model
Replacement

Description

T874D1165

51, 53 Obsolete. Carrier logo; part no. HH07AT162-03; °C
scaleplate; used with Q674B.

44

Remarks

Obsolete. Command-Aire logo.

See OEM for
replacement.
T874D1165a

Replacement thermostat has
°F scaleplate; set H1
anticipator for current draw of
fan and stage 1 heat primary.

T874D1165

D1298

90, 232 Obsolete. Singer special; °C scaleplate; controls two
separate heat/cool circuits; used with Q674D or
Q674G1054, G1062.

See OEM for
replacement.

D1306

90, 186 Obsolete. Trane special; part no. 02005949; controls
two separate heat/cool circuits; used with Q674G1013.

See OEM for
replacement.

D1314

44

Obsolete. McQuay logo; part no. 02005941; 12°F
(6.6°C) differential between H1 and H2.

T874D1165

D1322

46

Obsolete. Amana logo; part no. D68535-03; used with
Q674B1075; used in Y594D1149.

T874D1165

D1330

44

Obsolete. Trane logo; part no. 13080242; °C scaleplate.

T874D1165

Replacement has °F
scaleplate.

D1355

44

Obsolete. Climate Control special; part no. 02005942;
°C scaleplate; 6°C (11°F) differential between H1 and
H2.

T874D1165

Replacement has 2°F
differential between H1 and
H2.

D1363

44

Obsolete. McQuay logo; part no. 02005943; 12°F
(6.6°C) differential between H1 and H2; 6°F (3.3°C)
differential between C1 and C2.

T874D1165

Replacement has 2°F
differential between H1 and
H2; 2°F differential between
C1 and C2.

D1405

44

Obsolete. Trane logo; part no. 02005952; 12°F (6.6°C)
differential between H1 and H2; 6°F (3.3°C) differential
between C1 and C2.

T874D1165

Replacement has 2°F
differential between H1 and
H2; 2°F differential between
C1 and C2.

D1413

44

Obsolete. Trane logo; part no. 02005956; 12°F (6.6°C)
differential between H1 and H2.

T874D1165

Replacement has 2°F
differential between H1 and
H2.

D1421

44

Obsolete. Climate Control special; part no. 02005938;
°C scaleplate.

T874D1165

Replacement has °F
scaleplate.

D1439

90

McQuay logo; part no. 02005935; used with
Q674G1096.

T874D1165

D1447

90

Obsolete. Climate Control special; part no. 02005940;
°C scaleplate; used with Q674G1096.

T874D1165

Replacement has °F
scaleplate.

T874D1165a

Set H1 anticipator for current
draw of fan and stage 1 heat
primary.

D1454

D1462

51, 53 Obsolete. Carrier logo.

80

Obsolete. Fedders multi-logo; part no. THTX-220-A0HB,
88-58-00550-001; used with Q674E1205.

Replacement has °F
scaleplate; 2°F differential
between H1 and H2.

T874D1165

a

Both the thermostat and subbase must be replaced.

53

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

D1470

44

Trade Model
Replacement

Description
Obsolete. York logo; part no. 2TH04701624A; includes
Allen wrench and screws to lock cover; °C scaleplate.

T874D1165

D1488

44

Obsolete. Risco special.

T874D1165

D1496

44

Obsolete. Borg Warner multi-logo; part no.
6TH04701524A; includes Allen wrench and screws to
lock cover.

T874D1165

D1504

82

York logo; part no. 025-23321-000; °C scaleplate; used
with Q674E1007; used in Y594D1180.

T874D1165

Remarks
Replacement has °F
scaleplate.

Replacement has °F
scaleplate.

D1512

44

Honeywell logo; Heil Quaker part no. HQ712002HW.

T874D1165

D1520

44

Obsolete. Bard logo; adjustable lever stops set 68°F
(max. heat) and 78°F (min. cool).

T874D1165

D1538

44

Obsolete. McQuay logo; part no. 02005937.

T874D1165

D1553

44

Obsolete. Climate Control special; part no. 02005944;
°C scaleplate; 6°C differential between H1 and H2; 3°C
differential between C1 and C2.

T874D1165

D1561

44

Obsolete. General Electric logo; used with Q674 A-G.

T874D1165

D1587

44

Obsolete. Stiles Four Seasons logo.

T874D1165

D1595

139

Obsolete. Nepco logo; used with Q674F1394.

T874D1165/
Q674B1018a

D1603

44

Obsolete. Arcoaire logo.

T874D1165

D1611

44

Obsolete. No logo; Friedrich part no. AT5411; °F/°C
scaleplate.

T874D1165

Replacement has °F
scaleplate.

D1629

82

Obsolete. Reznor logo; °F/°C scaleplate; used with
Q674E1007; used in Y594D1248.

T874D1165

Replacement has °F
scaleplate.

D1678

44

Obsolete. Honeywell logo; Saudi Oger special; °C
scaleplate; one setpoint lever; used with Q674A-K.

T874D1165

Replacement has °F
scaleplate; separate heating
and cooling setpoint levers.

D1686

98

Obsolete. McQuay logo; part no. 60685501; 8°F (4.4°C)
differential between H1 and H2; 6°F (3.3°C) differential
between C1 and C2; used with Q674E1312.

T874D1165

Replacement has 2°F
differential between H1 and
H2; 2°F differential between
C1 and C2.

D1694

202

Obsolete. McQuay logo; part no. 60685201; used with
Q674G1120.

Replacement has 2°F
differential between H1 and
H2; 2°F differential between
C1 and C2; replacement has
°F scaleplate.

Replacement has HEAT-OFFCOOL system switching; no
LEDs.

See OEM for
replacement.

D1702

44

Obsolete. McQuay logo; part no. 60685101.

T874D1165

D1710

44

Trane logo.

T874D1165

D1728

44

York-Miraco logo.

T874D1165

D1744

44

American Standard logo; heat anticipator factory set at
0.4A.

T874D1165

D1751

44

Obsolete. Goettl logo; part no. 372080; range stops set
at 68°F (max. heating) and 78°F (min. cooling).

T874D1165

D1769

82

Obsolete. Arcoaire logo; part no. 1506753; °F/°C
scaleplate; used with Q674E1346; used in Y594D1297.

T874D1165

Replacement has °F
scaleplate.

D1777

44

Obsolete. Climate Control logo; part no. 65495806; °F/
°C scaleplate.

T874D1165

Replacement has °F
scaleplate.

D1785

82

Obsolete. Comfortmaker logo; part no. 1505753; °F/°C
scaleplate; used with Q674E1346; used in Y594D1305.

T874D1165

Replacement has °F
scaleplate.

D1793

44

Obsolete. McQuay logo; part no. 65495805; °F/°C
scaleplate.

T874D1165

Replacement has °F
scaleplate.

a

Both the thermostat and subbase must be replaced.

60-2485—8

54

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number
D1801
D1819

D1827

D1843

Fig.
No.

Trade Model
Replacement

Description

45, 208 Trol-A-Temp by Honeywell logo; H1 and H2 anticipators
set at 0.10A; used with Q674B1463, D1115.
44

Marv Air Com Stat logo; part no. 50059; adjustable
interstage between H1 and H2 and between C1 and C2;
includes Allen wrench and screws to lock cover; field
adjustable range stops; °F/°C scaleplate.

45, 208 Trol-A-Temp by Honeywell logo; Premier White® color;
H1 and H2 heat anticipators set at 0.10A; used with
Q674B1471, D1123.
45

None
T874D1165

None

Obsolete. Janitrol logo; Goodman part no. CHT 90-120;
used with Q674B1000; used in Y594D1321.

T874D1165

Remarks
See Trol-A-Temp for
replacement.
Replacement has a 2°F fixed
interstage differential between
H1 and H2 and between C1
and C2; replacement has °F
scaleplate.
See Trol-A-Temp.

D1850

44

Honeywell logo; Carrier part no. HH621606.

T874D1165

D1868

44

Bard logo; part no. 8405-031; H1 and H2 heat
anticipators factory set at 0.25A; 5°F interstage
differential between H1 and H2 and between C1 and C2;
includes Allen wrench and screws to lock cover; field
adjustable range stops.

T874D1165

Replacement has 2°F fixed
interstage differential between
H1 and H2 and between C1
and C2.

D1876

44

Obsolete. AAF/Snyder General logo; part no.
4ELN6981A; °F/°C scaleplate.

T874D1165

Replacement has °F
scaleplate.

Obsolete. Climate-Tel logo.

T874D1165

D1892

44

D1918

224,
225

Obsolete. AAF/Snyder General logo; °F/°C scaleplate;
no cooling anticipation; used with Q674E1312, C1298;
66804407.

See OEM for
replacement.

D1926

226

Obsolete. AAF/Snyder General logo; °F/°C scaleplate;
no cooling anticipation; used with Q674G1120;
66804406.

See OEM for
replacement.

D1934

44

Bard logo.

T874D1165

D1942

82

Honeywell logo; TRADELINE model; used with
Q674E1403; used in Y594D1347; designed to replace
York part no. 2TH04701024.

Y594D1347a

D1959

44

Rheem part no. 41-21444-01.

T874D1165

Obsolete. Desert Aire logo.

T874D1165

D1967

44

D1975

224,
225

Obsolete. McQuay part no. 066816603; °F/°C
scaleplate; no cooling anticipation.

See OEM for
replacement.

D1983

226

Obsolete. McQuay part no. 066816602; °F/°C
scaleplate; no cooling anticipation; used with
Q674G1120.

See OEM for
replacement.

D1991

51, 53 Carrier logo; Premier White® color; °C scaleplate.

T874D1165a

D2007

44

Ultra-Zone logo.

T874D1165

D2023

44

Honeywell logo; TRADELINE model; Premier White®
color; °C scaleplate; includes locking cover; used with
Q674A-K.

T874D1165

D2031

82

Obsolete. Honeywell logo; no cover; used with
Q674E1049 and TG504A1025; used in Y594D1354.

D2049

45, 72, Obsolete. Carrier Heat Pump System Control logo; part
55, 66, no. HH07AT236; °F/°C scaleplate; used with Q674B-D,
184 Q674G; used in Y594D.

Set H1 anticipator for total
current draw of fan and stage
1 primary; replacement has °F
scaleplate.
Replacement has °F
scaleplate and is beige.

T874D1165 or
Y594D1354
T874D1165

Replacement has °F
scaleplate.

a

Both the thermostat and subbase must be replaced.

55

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

D2056

44

Obsolete. ComStat logo; part no. 50056; °F/°C
scaleplate; adjustable interstage on both heating and
cooling; includes locking cover and field-adjustable
locking levers.

T874D1165

Replacement has °F
scaleplate and 2°F fixed
differential in heating and
cooling.

D2064

53

Obsolete. Carrier Weathermaker; part no. HH07AT209;
stage 1 and 2 heat anticipator factory set 0.1A; taupe
color; used with Q674E1445; used in Y594D1412.

T874D1165

Set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary.
Replacement is beige.

D2072

53

Obsolete. Carrier Zone Perfect; part no. HH07AT208;
taupe color; used with Q674E1445; used in Y594D1420.

T874D1165

Set stage 1 heat anticipator for
total current draw of fan and
stage 1 heat primary.
Replacement is beige.

D2080

139

Obsolete. Hydroheat logo.

T874D1165/
Q674B1018a

Replacement system switch:
HEAT-OFF-COOL; no LEDs.

D2098

44

Obsolete. Honeywell logo; °F scaleplate; one setpoint
lever; used with Q674D1008; used in Y594D1438.

T874D1165

Replacement has °F
scaleplate and two setpoint
levers

D2106

44

Obsolete. Honeywell logo; °C scaleplate; one setpoint
lever; used with Q674D1008; used in Y594D1446.

T874D1165

Replacement has °F
scaleplate and two setpoint
levers.

D2114

44

Obsolete. Bard logo; °C scaleplate.

T874D1165

Replacement has °F
scaleplate.

D2122

224,
225

Obsolete. McQuay

T874D2023

Replacement has °C
scaleplate.

T874D1165

Replacement has °F
scaleplate.

D2130

226

Trade Model
Replacement

Description

Obsolete. McQuay

See OEM for
replacement.

D2148

44

Obsolete. Dry Aire Systems logo; °F/°C scaleplate.

T874D1165

D2155

139

Hydroheat logo; Premier White® color; °F/°C scaleplate;
used with Q674F1634.

T874D1165/
Q674B1018a

D2163

208

Obsolete. Amana logo; part no. P1217501F; °F/°C
scaleplate.

T874D1165

D2171

44

Obsolete. Amana logo; part no. P1217701F; °F/°C
scaleplate.

T874D1942

D2189

44

Armstrong logo; part no. 01142A024; °F/°C scaleplate;
includes Air Ease insert.

T874D1165

D2197

44

Liebert logo; part no. 138968P3; °F/°C scaleplate;
interstage differential between H1 and H2 and between
C1 and C2; includes Allen wrench and screws to lock
cover; field-adjustable locking levers.

T874D1165

D2205

44

Aaon logo; Premier White® color; °F/°C scaleplate.

T874D1165

T874E

Replacement system switch:
HEAT-OFF-COOL; no LEDs.

0-stage heat, 2-stage cool.

E1008

44

Obsolete. Honeywell logo.

T874E1016

E1016

44

Honeywell logo; TRADELINE model; includes Allen
wrench and screws to lock cover; field-adjustable
locking levers.

T874E1016

E1024

44

Obsolete. Westinghouse logo.

T874E1016

E1032

44

Lennox logo; part no. 13F0901; °F/°C scaleplate.

T874E1016

E1040

72

Obsolete. Trane logo; used with Q674C1009; used in
Y594E1015.

T874E1016

a

Both the thermostat and subbase must be replaced.

60-2485—8

Remarks

56

Replacement has °F
scaleplate.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

E1081

44

Trane logo; part no. BAY28X186; °F/°C scaleplate.

T874E1016

Replacement has °F
scaleplate.

E1099

44

Obsolete. Lennox logo; part no. 13F1001; °C scaleplate.

T874E1016

Replacement has °F
scaleplate.

E1107

44

Honeywell logo; °C scaleplate.

T874E1016

Replacement has °F
scaleplate.

Description

E1123

44

Obsolete. Amana logo; part no. D68535-4.

T874E1016

E1149

44

Obsolete. York logo; part no. 2TH04701724A.

T874E1016

E1156

44

Obsolete. Borg Warner multi-logo; part no.
6TH04701724A.

T874E1016

E1164

44

Obsolete. E. A. Juffali & Bros. logo.

T874E1016

E1206

44

Obsolete. Trane logo.

T874E1016

E1230

44

Obsolete. Climar logo.

T874E1016

T874F

Remarks

2-stage heat, 0-stage cool.

F1007

44

Honeywell logo.

T874F1015

F1015

44

Honeywell logo; TRADELINE model; includes Allen
wrench and screws to lock cover; field-adjustable
locking levers.

T874F1015

F1023

44

Obsolete. Lennox logo; part no. 13F1101.

T874F1015

F1031

44

Obsolete. Honeywell logo; °C scaleplate; used with
40003440-001 wallplate; used in Y594F1022.

T874F1015

Replacement has °F
scaleplate.

F1049

44

Obsolete. Lennox logo; °C scaleplate.

T874F1015

Replacement has °F
scaleplate.

F1056

55,
66

Obsolete. Honeywell logo; stages 1 and 2 heat
electrically isolated; used with Q674D1008.

F1072

44

Obsolete. Wesco logo; heat anticipator factory set at
0.8A.

T874F1015

F1098

189

Obsolete. Lennox logo; used with Q674D1008 to control
an M839.

T874F1015

F1106

95

Obsolete. Oneida logo; part no. 30A0287-02; used with
Q674K1018 on combination wood and oil applications.

T874F1155

F1114

44

Honeywell logo; Honeywell Canada TRADELINE model;
°C scaleplate; includes Allen wrench and screws to lock
cover; field-adjustable locking levers.

T874F1015

Replacement has °F
scaleplate.

F1122

62

Obsolete. Honeywell logo; two heat setpoint levers;
used with Q674B1307.

T874F1015/
Q674D1040

Replacement has no LED.

T874F1015

Replacement has °F
scaleplate.

F1130

72, 91 Obsolete. Reznor logo; °F/°C scaleplate; used with
Q674C, D, or G; used with Q674C1009, G1005; used in
Y594F1048.

None

F1148

44

Obsolete. Trane logo; part no. THT 0584.

T874F1015

F1155

95

Honeywell logo; used with Q674K1026 on combination
wood and oil applications.

T874F1155

T874G
G1006

Set H1 and H2 anticipators to
lowest settings.

Heat pump models; 2-stage heat, 1-stage cool;
1–stage changeover.
84, 155 Obsolete. Honeywell logo; used with Q674E1015.

Y594G1252a

Wiring differences (old=new):
R=O, M=Y, F=G, V=R, Y=W2;
E-W2 jumper required.

a

Both the thermostat and subbase must be replaced.

57

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

Description

Remarks

G1014

86, 150 Obsolete. Lennox logo; part no. 24F5801; °F/°C
scaleplate; H2 anticipator factory set at 0.25A for fast
cycle performance; changeover in cooling mode;
independent heating and cooling circuits; used with
Q674E1148, F1113.

Y594G1252

G1022

86, 150 Obsolete. Lennox logo; part no. 24F5701; °F/°C
scaleplate; H2 anticipator factory set at 0.25A for fast
cycle performance; changeover in cooling mode;
independent heating and cooling circuits; used with
Q674E1148, F1113.

Y594G1252a

Wiring differences (old=new):
R=O, M=Y, F=G, Y=W2,
V-VR=R (must use single
transformer).

Y594G1252a

Wiring differences when
replacing T874G/Q674J1019
(old=new): W=W2.

None

See subbase description for
replacement information.

Y594G1419

Wiring differences (old=new):
C=X; jumper Y1-W1.

Wiring differences (old=new):
A=L.

G1048

153,
159

Obsolete. Westinghouse logo; H2 anticipator factory set
at 1.2A; used with Q674F1121, J1019.

G1055

161

Carrier Heat Pump System Control logo; part no.
HH07AT171; H2 anticipator factory set at 0.8A;
changeover in cooling mode; used with Q674J1035
(HH93AZ173).

G1071

50, 103, Obsolete. Carrier Heat Pump System Control logo;
126, meets DoD specifications; H2 anticipator factory set at
183 0.8A; used with Q674P1005 (HH93AZ169), L1041
(HH93AZ175), B1158, or J1050.

a

Wiring differences (old=new):
R=O, M=Y, F=G, Y=W2,
V-VR=R (must use single
transformer).

G1089

154

Obsolete. Marvair logo; special for Crispaire; H2
anticipator factory set at 1.2A; used with Q674F1204;
used in Y594G1153.

Y594G1393a

G1097

155

Obsolete. Honeywell logo; Rheem part no. ZXMT-B79;
used with Q674F1238 (41-20797-14).

Y594G1252a

G1105

153

Obsolete. Heat Wave (Southwest Mfg.) logo; H2
anticipator factory set at 1.2A; used with Q674F1170.

Y594G1252a

G1113

103

Obsolete. Carrier Heat Pump System Control logo;
meets DoD specifications; H2 anticipator factory set at
0.8A; used with Q674L1041.

Y594G1419a

Wiring differences (old=new):
C=X; jumper Y1 -W1.

G1121

103

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT161; °C scaleplate; H2 anticipator factory
set at 0.8A; includes Allen wrench and screws to lock
cover.

Y594G1419a

Wiring differences (old=new):
C=X; jumper Y1-W1.

G1139

143,
234

Obsolete. Honeywell logo; used with Q674B1240,
C1108.

None

See subbase description for
replacement information.

G1147

148

Obsolete. Honeywell logo; changeover in cooling mode;
used with Q674F1139.

Y594G1252a

Wiring differences (old=new):
C=X.

Y594G1252a

See subbase description for
replacement information.
W1-Y1 jumper required.

G1154

84, 139 Obsolete. Lennox logo; used with Q674E1015, F1105.

G1162

155

Obsolete. Lennox logo; meets DoD specifications; used
with Q674F.

Y594G1419a

G1170

160

Obsolete. York logo; part no. 2TH11702424A; H2
anticipator is fixed; used with Q674J1027; used in
Y594G1013.

Y594G1567a

G1188

147

Obsolete. Honeywell logo; Keeprite/Westinghouse
special; H2 anticipator factory set 1.2A; °C scaleplate;
changeover in cooling mode; used with Q674F1295.

Y594G1252a

G1196

160

Obsolete. York logo; °C scaleplate; changeover in
cooling mode; used with Q674J1027; used in
Y594G1138.

Y594G1567a

a

Both the thermostat and subbase must be replaced.

60-2485—8

58

Wiring differences (old=new):
S=L.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

G1204

162

Honeywell logo; designed for use on Trane heat pumps;
no H2 anticipation; changeover in cooling mode; used
with Q674J1043 and C815A1005; used in Y594G1161.

Y594G1161

G1212

155

Obsolete. Honeywell logo; H2 anticipator factory set at
0.2A; changeover in cooling mode; includes shunt to
bypass H2 anticipator with W3 heat relays; used with
Q674F1238.

Y594G1252a

G1220

235

Obsolete. Rheem logo; part no. RXMT-C71; changeover
in cooling mode; used with Q674F1238.

Y594G1252a

G1238

155

Obsolete. Ruud logo; part no. UXMT-C71; changeover
in cooling mode; used with Q674F1238.

Y594G1252a

G1246

Trade Model
Replacement

Description

a

Remarks
Designed for use on Trane
heat pumps.

Obsolete. Honeywell logo; changeover in cooling mode.
155

Used with Q674F1212; used in Y594G1195, G1252,
G1369.

Y594G1252a

170

Used with Q674F1410; used in Y594G1393.

Y594G1393a

G1261

58, 157 Obsolete. Borg-Warner; used with Q674D1032, F1253.

None

See subbase description for
replacement information.

G1279

58, 157 Obsolete. Bryant logo; used with Q674D1032, F1253.

None

See subbase description for
replacement information.

G1287

58, 157 Obsolete. Wesco logo; used with Q674D1032, F1253.

None

See subbase description for
replacement information.
Wiring differences (old=new):
Y=Y2, O=Y1, W=W2; jumper
W1-Y2.

G1295

58

Obsolete. York logo; part no. 2TH11702724A; used with
Q674D1032.

T874D1165/
Q674D1040

G1345

160

Obsolete. York logo; part no. 2TH11702624A; °C
scaleplate; used with Q674J1027.

Y594G1575a

G1352

73

Obsolete. Command-Aire logo; 12°F differential
between H1 and H2 for night setback; used with
Q674C1066.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none; RL jumper required; no night
setback.

T8600D1004 Wiring differences (old=new):
(programmable) Y1=O, Y2=Y, L=RH; RC-RH
jumper required; includes
night setback.
G1378

79

Obsolete. Mammoth logo; H2 anticipator factory set at
0.8A; 12°F differential between H1 and H2 for night
setback; °F/°C scaleplate; used with Q674C1124; used
in Y594G1294.

Y594H1012a

Wiring differences (old=new):
R1=none, R2=L; R-L jumper
required; no night setback.

T8090A1007/ Includes night setback; W-Y
Q682A1038a jumper required.
(programmable)
G1402

129

Obsolete. York part no. 2TH11702824A; meets DoD
specifications; used with Q674L1363.

G1410

155

Obsolete. Borg-Warner multi-logo; part
no. 6TH11703024A; used with Q674F1311.

G1428

160

Obsolete. Borg-Warner multi-logo; part no.
6TH11702424A; used with Q674J1027; used in
Y594G1229.

Y594G1567a

G1436

58

Obsolete. Borg-Warner multi-logo; part no.
6TH11702724A.

T874D1165/
Q674D1040

Y594R1425a

Wiring differences (old=new):
W=W2, X=E, B=X; jumper
Y-W1.

T874G1246a or
Y594G1252a

Wiring differences (old=new):
Y=Y2, O=Y1, W=W2; jumper
W1-Y2.

a

Both the thermostat and subbase must be replaced.

59

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

G1444

160

Obsolete. ROCA logo; °C scaleplate; used with
Q674J1027.

G1451

155

Obsolete. BDP multi-logo; part no. HH641502; used with T874G1246a or
Q674F1212; used in Y594G1245.
V594G1252a

G1469

194

Obsolete. No logo; Addison special; used with
Q674F1345; used in Y594G1344.

G1485

163

Obsolete. AAF logo; part no. 4ELN-7839; °F/°C
Y594G1393a
scaleplate; 10°F differential between H1 and H2 for night
setback and momentary RESET system switch position; T8611G1004
used with Q674C1199.
(programmable)

Description

Y594G1567a

Y594G1252a

Remarks
Replacement has °F
scaleplate.

Wiring differences (old=new):
Y1=O, C=X, W1=Y1, X=L.
No night setback or
momentary reset switch.
Includes night setback; no
momentary reset switch.

G1493

167

Obsolete. Honeywell logo; Rheem part no. 41-2079718; used with Q674F1360.

Y594G1526a

G1501

195

Obsolete. Coleman logo; part no. 3600-375; changeover
in cooling mode; used with Q674F1378.

Y594G1252a

G1535

163

Obsolete. AAF/Snyder General logo; 4ELN7839 °F/°C
Y594G1393a No night setback or
scaleplate; 10°F differential between H1 and H2 for night
momentary reset switch.
setback and momentary RESET system switch position; T8611G1004 Includes night setback.
used with Q674C1199.
(programmable)

G1543

194

Obsolete. Addison logo; Weather King part no. 8403197; used with Q674F1345; used in Y594G1328.

Y594G1252a

Wiring differences (old=new):
Y1=O, C=X, W1=Y, X=L.

G1568

160

Obsolete. Luxaire logo; part no. 026-00068-000; °C
scaleplate; used with Q674J1126; used in Y594G1351.

Y594G1367a

Replacement has °F
scaleplate.

G1576

169

Obsolete. Coleman logo; part no. 3600-373; changeover
in heating and cooling mode; used with Q674F1402;
used in Y594G1377.

Y594G1633a

G1584

73

Obsolete. No logo; Friedrich part no. AT5784; 8°F
(4.4°C) differential between H1 and H2; used with
Q674C1223.

Y594H1012a

Wiring differences (old=new):
L1=L; changeover in cooling
only.

Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none;
L-R jumper required; no night
setback.

T8611G1004 Includes night setback.
(programmable)
G1592

155

Obsolete. Arcoaire logo; used with Q674F1212; used in
Y594G1385.

G1600

199

Obsolete. Honeywell logo; meets DoD specifications;
used with Q674F1428; used in Y594G1401.

Y594G1419a

Wiring differences (old=new):
jumper W1-Y1.

G1618

73

Obsolete. Honeywell logo; 12°F differential between H1
and H2 for night setback; used with Q674C1256.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none;
L-R jumper required; no night
setback.

T874G1246a or
Y594G1252a

T8600C1162 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; includes night
setback.
G1626

167

Honeywell logo; used with Q674F1436; used in
Y594G1526.

G1642

227

Honeywell logo; TRADELINE model; meets DoD
specifications; used with Q674F1444; used in
Y594G1419.

a

Both the thermostat and subbase must be replaced.

60-2485—8

60

None
Y594G1419a

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

G1659

177

Trade Model
Replacement

Description
Obsolete. Mammoth logo; 0.8A maximum current
through B or O terminal; 12°F differential between H1
and H2 for night setback; used with Q674C1330; used in
Y594G1427.

Y594H1012

a

Remarks
Wiring differences (old=new):
R2=L, R1=none; L-R jumper
required; no night setback.

T8611G1004 Includes night setback.
(programmable)

G1675

174

Obsolete. American Standard logo; part no.
ASYSTAT650; used with Q674J1142; used in
Y594G1443.

Y594G1161a

G1691

176

Obsolete. Command Aire logo; part no. P1013-0060;
12°F (6.6°C) differential between H1 and H2 for night
setback; used with Q674C1389, C1397.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y, R=none; L-R
jumper required; no night
setback.

T8611G1004 Includes night setback.
(programmable)
G1717

175

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT102N; used with Q674J1167; used in
Y507J1201.

Y594G1252a

Wiring differences (old=new):
C=X, D=L; replacement has
AUX. HEAT and EM. HEAT
LEDs.

G1741

227

Honeywell logo; TRADELINE model; includes factory
set range stops at 68°F (max. heat) and 78°F (min.
cool); Premier White® color; used with Q674F1477;
used in Y594G1476.

Y594G1476a

G1758

211

Trol-A-Temp by Honeywell logo; Premier White® color;
changeover is provided by Trol-A-Temp zone panel;
used with Q674F1485; used in Y594G1492.

None

G1774

216

Obsolete. Comfortmaker logo; part no. 1505756; used
with Q674J1175; used in Y594G1500.

Y594G1252a

Wiring differences (old=new):
E=W2, W1=W3, X=E, C=X.

G1782

216

Obsolete. Arcoaire logo; part no. 1506756; used with
Q674J1175; used in Y594G1518.

Y594G1252a

Wiring differences (old=new):
E=W2, W1=W3, X=E, C=X.

G1790

161

Obsolete. Carrier logo; Premier White® color; °C
scaleplate; includes Allen wrench and screws to lock
cover; used with Q674J1191.

Y594G1252a

Wiring differences (old=new):
C=X; replacement has °F
scaleplate.

G1816

163

Climate Master logo; part no. AT5716; °F/°C scaleplate;
10°F differential between H1 and H2 and momentary
RESET system switch position.

Y594G1393a

No momentary reset switch.

G1824

227

Honeywell logo; Australian TRADELINE model; Premier
White® color; °C scaleplate; used with Q674F1477;
used in Y594G1534.

Y594G1476a

G1832

231

Obsolete. Intertherm logo; used with Q674F1519; used
in Y594G1542.

Y594G1252a

Replacement has auto
changeover in cooling mode
only.

G1840

231

Obsolete. Miller logo; used with Q674F1519; used in
Y594G1559.

Y594G1252a

Replacement has auto
changeover in cooling mode
only.

G1857

229

Obsolete. Lennox logo; °C scaleplate; Premier White®
color; used with Q674F1535; used in Y594G1583.

Y594G1161a

Wiring differences (old=new):
E=X2, C=B, L=F.

G1865

160

Honeywell logo; TRADELINE model; designed to
replace Y594G1013 (York part no. 2TH11702424),
Y594G1229 (York part no. 6TH11702424), and York part
no. 2TH117704124); used with Q674J1209; used in
Y594G1567.

Y594G1567a

See Trol-A-Temp for
replacement.

a

Both the thermostat and subbase must be replaced.

61

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

G1873

160

Obsolete. Honeywell logo; TRADELINE model; Premier
White® color; designed to replace Y594G1013 (York
part no. 2TH11702424), Y594G1229 (York part no.
6TH11702424), and York part no. 2TH117704124); used
with Q674J1225; used in Y594G1575.

Y594G1567

G1881

167

Rheem; part no. 41-20797-18.

Y594G1526a

G1899

169

Obsolete. Amana; part no. 10574101; used with
Q674F1550; used in Y594G1591.

Y594G1633a

G1915

155

Econar logo; used with Q674F1212; used in
Y594G1609.

Y594G1252a

170

Used with Q674F1410.

Y594G1393a

176

Trane logo; part no. X13510599010; H2 make 12°F
below H1 make.

Y594H1012a

G1923

Trade Model
Replacement

Description

a

Remarks
Replacement is beige.

Wiring differences (old=new):
Y1=O, Y2=Y, R=none; L-R
jumper required; no night
setback.

T8611G1004 Includes night setback.
(programmable)
G1931

155,
170

G1949

73

Obsolete. Honeywell logo; Premier White® color; °C
scaleplate; used with Q674F1568.
Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT204; °F/°C scaleplate; H2 make 8°F below
H1 make; used in Y594.

None
Y594H1012a

See subbase description for
replacement information.
Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none; RL jumper required; no night
setback.

T8600D1004 Wiring differences (old=new):
(programmable) Y1=O, Y2=Y, L=RH; RC-RH
jumper required; includes
night setback.
G1956

30, 103, Obsolete. Carrier logo; Canada; Premier White® color;
126, °C scaleplate; includes locking cover.
183

Y594G1476

Replacement has °F
scaleplate.
Replacement has °F
scaleplate.

G1964

160

York logo; Canada; Premier White® color; °C scaleplate;
used in Y594G1625.

Y594G1575a

G1972

169

Honeywell logo; TRADELINE model; used with
Q674F1584; used in Y594G1633.

Y594G1633a

G1980

169

Obsolete. Amana logo; part no. 10574103; used with
Q674F1600; used in Y594G1641.

Y594G1633a

G1998

155

Obsolete. Tempstar logo (Inter-City Products); used in
Y594G1658; used with Q674F1212.

Y594G1252a

G2004

103

Honeywell logo; TRADELINE model; used with Q674L;
used in Y594G.

Y594G1666

161

Used with Q674J1274; used in Y594G1674.

Y594G1674

155,
170

WaterFurnace logo; part no. TA21H03; Premier White®
color; °F/°C scaleplate; used with Q674F1667; used in
Y594G1716.

Y594G1716

G2046

T874H

Wiring differences (old=new):
W3=W2.

Heat pump model; 1-stage heat, 1-stage cool,
1-stage changeover in cool.

H1005

74

Obsolete. Command Aire logo; used with Q674C1041.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required.

H1013

74

Obsolete. Friedrich part no. AT5813; °C scaleplate; used
with Q674C1041.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required; replacement has °F
scaleplate.

a

Both the thermostat and subbase must be replaced.

60-2485—8

62

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

H1021

74

H1039

Trade Model
Replacement

Description

Remarks

Obsolete. Friedrich Climate Master logo; part no.
AT5821; °F/°C scaleplate; used with Q674C1041.

Y594H1012

a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required; replacement has °F
scaleplate.

79

Obsolete. Mammoth logo; °F/°C scaleplate; used with
Q674C1124; used in Y594H1004.

Y594H1012a

Wiring differences (old=new):
R1=R, R2=L.

H1054

74

Obsolete. No logo; Friedrich part no. AT5854; used with
Q674C1041.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required.

H1062

164

Honeywell logo; used with Q674C1249; used in
Y594H1012.

Y594H1012a

H1070

172,
173

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT166; °C scaleplate; used with Q674B1406
(HH93AZ200) or Q674C1322 (HH93AZ199).

None

See subbase description for
replacement information.

H1088

172,
173

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT167; used with Q674B1406 (HH93AZ200)
or Q674C1322 (HH93AZ199).

None

See subbase description for
replacement information.

H1096

177

Obsolete. Mammoth Water Source Heat Pump logo; °F/
°C scaleplate; changeover stage 0.8A maximum; used B
or O terminal; used with Q674C1330.

Y594H1012a

Wiring differences (old=new):
R1=R, R2=L; L-R jumper
required.

H1112

74

No logo; Friedrich part no. AT5812; used with
Q674C1355.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required.

H1120

205

Obsolete. Command Aire logo; part no. P1013-0055;
used with Q674C1389, C1397.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y.

H1138

221

Obsolete. Climate Master logo; part no. AT5838; used
with Q674C1470.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; replacement has
MALFUNCTION LED only.

H1146

205

Trane logo; part no. X13510598010.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y.

H1153

173

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT167; °F/°C scaleplate; used with
Q674C1322; used in Y594H1053.

None

See subbase description for
replacement information.

H1161

74

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT203; °F/°C scaleplate; used with
Q674C1496; used in Y594H1038.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required.

J1002

124,
144,
206,
207

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT175; used with Q674J1068 (HH93AZ183),
Q674J1159 (HH93AZ196), Q674L1074 (HH93AZ186),
Q674L1637 (HH93AZ195).

None

See subbase description for
replacement information.

J1010

124,
171

Obsolete. BDP multi logo; part no. 34427DP124/P2722471; used with Q674J1084, L1371.

None

See subbase description for
replacement information.

J1028

124,
144,
206,
207

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT165; °C scaleplate; used with Q674J1068
(HH93AZ183), Q674J1159 (HH93AZ196), Q674L1074
(HH93AZ186), Q674L1637 (HH93AZ195).

None

See subbase description for
replacement information.

J1036

124,
171

Obsolete. Miller logo; part no. 9132230; used with
Q674J1217.

T8511G1021

J1044

124,
171

Obsolete. Intertherm logo; part no. 9132240; used with
Q674J1217.

T8511G1021

J1051

124,
144

Obsolete. Carrier logo; part no. HH07AT165-W; Premier
White® color; °C scaleplate.

None

T874J

Heat pump model. 2-stage heat, 1-stage cool.

See subbase description for
replacement information.

a

Both the thermostat and subbase must be replaced.

63

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

J1069

124,
144,
206,
207

Obsolete. Honeywell logo; TRADELINE model; used
with Q674J1282; used in Y594J1019.

T8511G1021

J1077

124,
171

Obsolete. Nordyne logo; part no. 9148300; °F/°C
scaleplate.

T8511G1021

T874K

Trade Model
Replacement

Description

Remarks

Heat pump model; 2-stage heat, 1-stage cool, automatic
changeover in heat.

K1001

77

Obsolete. LSI Mammoth logo; used with Q674C1090.

Y594G1419a

Wiring differences (old=new):
RH-RC=R, W1=B, W3=W2,
W2=W1; remove Y1-W1
jumper.

K1019

181

Obsolete. McQuay/Snyder General logo; part no.
60687301; °F/°C scaleplate; H1 anticipator set at 0.83A;
8°F interstage differential between H1 and H2 for night
setback; used with Q674C1280.

Y594G1252a

Wiring differences (old=new):
C=X, W=B, A=L; jumper
E-W2; no night setback.

K1027

181

T874L

Obsolete. AAF/Snyder General logo; part no.
066804403; °F/°C scaleplate; H1 anticipator set at
0.83A; 8°F interstage differential between H1 and H2 for
night setback; used with Q674C1280.

T8611G1004 Wiring differences (old=new):
(programmable) C=X, W=B, A=X2; jumper X2R; remove external time clock;
includes night setback.
Y594G1252a

Wiring differences (old=new):
C=X, W=B, A=L; jumper
E-W2; no night setback.

T8611G1004 Wiring differences (old=new):
(programmable) C=X, W=B, A=X2; jumper
X2-R; remove external time
clock; includes night setback.

Heat pump model; 2-stage heat, 1-stage cool,
changeover in cool.

L1000

198

Obsolete. Carrier logo; part no. HH07AT176; used with
Q674E1270 (HH93AZ189).

Y594G1419a

L1018

138,
165

Obsolete. Carrier Multiplex System logo; part no.
HH07AT178; used with Q674B1356 (HH93AZ192) or
Q674C1264 (HH93AZ193).

See OEM for
replacement.

L1026

198

Obsolete. Honeywell logo; BDP part no. P272-2786;
used with Q674E1304.

Y594G1419a

E-W2 jumper required.

L1034

203

Obsolete. McQuay logo; part no. 60687201; °F/°C
scaleplate; H1 anticipator factory set at 0.83A; used with
Q674C1280.

Y594G1419a

Wiring differences (old=new):
Y=Y1, W=B, A=X1; remove
Y1-W1 jumper.

L1059

215,
213

Obsolete. Carrier logo; part no. HH07AT192; used with
Q674B1448 (HH93A2202) or Q674C1413
(HH93AZ204).

See OEM for
replacement.

L1067

203

Obsolete. AAF/Snyder General logo; part no.
066804402; H1 anticipator factory set at 0.83A; used
with Q674C1280.

Y594G1419a

L1075

203

Obsolete. McQuay logo; part no. 073318601; Premier
White® color; °F/°C scaleplate; includes AAF insert.

See OEM for
replacement.

T874N

Wiring differences (old=new):
Y=Y1, W=B, A=X1; remove
Y1-W1 jumper.

Heat pump model; 2-stage heat; 1-stage cool plus
changeover; changeover in heat mode.

N1008

178

Obsolete. Williamson logo; used with Q674F1196; used
in Y594N1007.

T874N1016

N1016

178

Honeywell Heat Pump Thermostat logo; used with
Q674F1220.

T874N1016

N1024

179,
217

Bard logo; H1 and C1 anticipation fixed; used with
Q674F1261.

None

a

Both the thermostat and subbase must be replaced.

60-2485—8

E-W2 jumper required.

64

See subbase description for
replacement information.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

N1040

179

Obsolete. Honeywell logo; H1 and C1 anticipation fixed;
used with Q674F1261; used in Y594N1015.

None

N1057

178

Obsolete. Intertherm logo; part no. 9111882; used with
Q674F1220; used in Y594N1023.

T874N1016

N1065

178

Obsolete. Miller logo; Nordyne part no. 9122240; used
with Q674F1220; used in Y594N1031.

T874N1016

T874P
P1006

Trade Model
Replacement

Description

Remarks

Heat pump model; 2-stage heat, 1-stage cool, automatic
changeover in cool.
57, 78 Obsolete. McQuay logo; part no. 860-442725B-00; 8°F
(4.4°C) interstage differential between H1 and H2; used
with Q674B1273, C1140.

None

See subbase description for
replacement information.

P1014

78

Obsolete. Friedrich/Climate Master logo; °F/°C
scaleplate; 8°F (4.4°C) differential between H1 and H2
for night setback; used with Q674C1207.

P1022

97

Obsolete. Friedrich/Climate Master logo; part no.
AT5922; °F/°C scaleplate; 8°F (4.4°C) differential
between H1 and H2 for night setback; used with
Q674C1215.

None

See subbase description for
replacement information.

P1030

97

Obsolete. No logo; Friedrich part no. AT5930; 8°F
(4.4°C) differential between H1 and H2 for night setback;
used with Q674C1215.

None

See subbase description for
replacement information.

68, 97 Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AT205; °F/°C scaleplate; heat interstage
differential 8°F (4.4°C).

None

See subbase description for
replacement information.

P1055

T874Q

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; includes night
setback.

1-stage heat; used with another T874 for night setback.

Q1005

44

Honeywell logo.

T874A1036

Q1013

44

Obsolete. Lennox logo; part no. 13F1201; °F/°C
scaleplate.

T874A1036

Replacement has °F
scaleplate.

Q1021

44

Obsolete. Lennox logo; part no. 13F1301; °C scaleplate.

T874A1036

Replacement has °F
scaleplate.

T874R

Heat pump model; 2-stage heat, 1-stage cool, manual
changeover.

R1004

47

Obsolete. Honeywell logo; used with Q674B1042; used
in Y594R1029.

Y594R1243a

Wiring differences (old=new):
W1=W2.

R1012

47

Obsolete. Honeywell logo; Addison heat pump; used
with Q674B1109.

Y594R1243a

Wiring differences (old=new):
W1=W2.

R1020

102

Obsolete. Lennox logo; part no. 24F5401; °F/°C
scaleplate; H1 and C1 anticipators are fixed; auxiliary
heat circuit powered by separate transformer; used with
Q674L1025.

Y594R1243a

Wiring differences (old=new):
M=Y, F=G, V-VR=R, Y=W2,
R=O; replacement has °F
scaleplate.

R1038

102

Obsolete. Lennox logo; °C scaleplate; H1 and C1
anticipators are fixed; auxiliary heat circuit powered by
separate transformer; used with Q674L1025.

Y594R1243a

Wiring differences (old=new):
M=Y, F=G, V-VR=R, Y=W2,
R=O; replacement has °F
scaleplate.

R1046

120,
101

Obsolete. York logo; part no. 2TH11702224A; H2
anticipator is fixed; used with Q674L1272 in Y594R1011
or with Q674L1094.

Y594R1664a

R1053

109

Obsolete. Honeywell logo; H2 anticipator is fixed; used
with Q674L1140; used in Y594R1136.

Y594R1763a

Designed for use on Trane
heat pumps.

R1061

104

Obsolete. Honeywell logo; H2 anticipator is field
adjustable; changeover in cooling; used with
Q674L1082.

Y594R1243a

Replacement has auto fan in
Emergency Heat mode.

a

Both the thermostat and subbase must be replaced.

65

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

R1079

123

Obsolete. Ruud logo; part no. UXMT-C70; used with
Q674L1157.

Y594R1243

R1087

120

Obsolete. Honeywell logo; Special for Dunham Bush;
use with Q674L.

Y594R1664a

R1095

123

Obsolete. Rheem logo; part no. RXMT-C70; used with
Q674L1157.

T874R1152/
Y594R1243a

R1103

104

Obsolete. Westinghouse logo; used with Q674L.

Y594R1243a

R1111

116,
104

Obsolete. Marvair logo; H2 anticipator factory set at
1.2A; used with Q674L1215, L1082; used in
Y594R1128.

Y594R1243a

Replacement has auto fan in
Emergency Heat mode.

R1129

113

Bard logo; used with Q674L1181.

Y594R1243a

Wiring differences (old=new):
X1=X.

R1137

108,
125

Obsolete. Honeywell logo; Heil Quaker part no.
HQ711597HW; used with Q674L1132; used in
Y594R1110.

Y594R1292a

R1145

120

Obsolete. York logo; °C scaleplate; H2 anticipator is
fixed; used with Q674L1272; used in Y594R1102.

Y594R1664a

R1152

115

Honeywell logo; used with Q674L1207, L1033; used in
Y594R1243.

Y594R1243a

R1160

182

Obsolete. Honeywell Advanced Heat Pump System
logo; used with Q674L1298 and W89.

R1178

110,
111

Obsolete. Lennox logo; part no. 24F5601; °F/°C
scaleplate; auxiliary heat circuit powered by separate
transformer; fast cycle stage H2 anticipator; requires
outdoor reset and independent circuits; used with
Q674L1165, L1355.

R1186

182

Obsolete. Honeywell Advanced Heat Pump System
logo; used with Q674L1231 and W89.

R1194

115

Obsolete. Amana logo; used with Q674L1249 and W89.

Y594R1243a

R1202

201

Obsolete. Intertherm logo; part no. 9111871; used with
Q674L1264 or Q674L1595; used in Y594R1185.

Y594R1672a

Wiring differences (old=new):
W2=W, Z=no connection,
K=X, W=G, W1=H, X=B.

R1210

101

Obsolete. Roca logo; °C scaleplate; used with
Q674L1017.

Y594R1243a

Wiring differences (old=new):
W=W2, X=L, B=X.

R1228

120

Obsolete. York logo; part no. 2TH11702524A; °C
scaleplate; used with Q674L1272 and C815A1005;
used in Y594R1144.

Y594R1672a

R1236

115

Obsolete. Williamson logo; includes Allen wrench and
screws to lock cover; used with Q674L1348.

T874R1152

R1244

115

Obsolete. Westinghouse logo; used with Q674L1314
and W89.

T874R1152/
Y594R1243a

R1251

120

Obsolete. York logo; part no. 2TH11702324A; H2
anticipator is fixed; used with Q674L1272 and
C815A1039.

Y594R1672a

R1269

122

Obsolete. Fedders multi logo; part no.
THTX-120-HEHB 88-58-00540-001; used with
Q674L1066; used in Y594R1037.

Y594R1615a

R1285

123

Obsolete. Honeywell logo; Rheem part no. 41-2079615; used with Q674L1157.

Y594R1243a

R1301

113

Obsolete. Comfortmaker logo; part no. 1505-714; used
with Q674L1181; used in Y594R1417.

Y594R1243a

Description

a

Both the thermostat and subbase must be replaced.

60-2485—8

66

Remarks

a

None
Y594R1763a

Wiring differences (old=new):
V-VR=R, M=Y, F=G, X=B,
Y=W, A=T, R=O, E=X2.

None

Wiring differences (old=new):
K=E, C=X, W1=B, Z=L.

Wiring differences (old=new):
X1=X.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacement

R1319

191

Obsolete. Carrier part no. 42QH400083; used with
Q674B1281 on two speed fan applications.

See OEM for
replacement.

R1327

120

Obsolete. Borg-Warner multi-logo; part no.
6TH11702224A; used with Q674L1272; used in
Y594R1193.

Y594R1672a

R1335

106

Obsolete. BDP multi-logo; part no. HH641501; H2
anticipator factory set 1.2A; used with Q674L1405; used
in Y594R1201.

Y594R1243a

R1343

133

Obsolete. Fedders multi-logo; part no.
THTX-120-HEHC 88-58-0056-001; used with
Q674L1413; used in Y594R1219.

Y594R1425a

Wiring differences (old=new):
K=E, C=X1, Z=L; remove
Y1-W1 jumper.

R1350

113

Obsolete. Honeywell logo; used with Q674L1181.

Y594R1243a

Wiring differences (old=new):
X1=X.

R1368

125

Obsolete. Coleman logo; part no. 3600-368; used with
Q674L1421; used in Y594R1235.

Y594R1797a

R1376

115

Honeywell logo; °C scaleplate; used with Q674L1207.

T874R1152

R1384

131,
135

Obsolete. Carrier Heat Pump System Control logo; part
no. HH07AQ170; used with Q674L (HH93AZ187),
Q674L (HH93AZ197), or Q674L (HH93AZ198).

Y594G1243a

Wiring differences (old=new):
C=X.

R1392

128

Obsolete. Williamson logo; used with Q674L1447; used
in Y594R1250.

Y594R1425a

Wiring differences (old=new):
A=L.

R1400

113

Obsolete. LSI part no. 104710001; used with
Q674L1181, L1462.

R1426

136

Obsolete. Trane Weathertron Heat Pump logo; part no.
BAYSTAT339 (WY28X0112); °F/°C scaleplate; used
with Q674L1496; used in Y594R1284.

Y594R1763a

R1434

134

Ruud logo; part no. 41-20796-32; used with Q674L1504;
used in Y594R1649.

Y594R1300a

R1442

134

Rheem logo; part no. 41-20796-28; used with
Q674L1504; used in Y594R1631.

Y594R1300a

R1459

134

Obsolete. Honeywell logo; Rheem part no. 41-2079625; used with Q674L1504.

Y594R1300a

R1467

108

Honeywell logo; used with Q674L1512; used in
Y594R1292.

Y594R1292a

R1475

123

Honeywell logo; scale range 42°F to 88°F; used with
Q674L1520; used in Y594R1300.

Y594R1300a

R1483

130

Obsolete. Comfortmaker logo; °F/°C scaleplate; used
with Q674L1538 and C815A1005; used in Y594R1318.

Y594R1763a

R1491

137

Obsolete. Honeywell logo; TRADELINE model; used
with Q674L1553; used in Y594R1326.

Y594R1615a

R1509

47

Obsolete. Slant/Fin logo; used with Q674B1042; used in
Y594R1334.

Y594R1243a

Wiring differences (old=new):
W1=W2.

R1517

130

Obsolete. Arcoaire logo; part no. 150671; used with
Q674L1538 and C815A1005; used in Y594R1342.

Y594R1763a

Wiring differences (old=new):
W1=W, E=X2, X=F, C=B.

R1525

113

Obsolete. Arcoaire logo; used with Q674L1181; used in
Y594R1359.

Y594R1243a

Wiring differences (old=new):
X1=X.

R1541

67

Obsolete. Goettl logo; part no. 372071; used with
Q674B1349.

Y594R1300a

R1558

134

Obsolete. Universal Parts logo; part no. 41-20796-45;
used with Q674L1504; used in Y594R1623.

Y594R1300a

R1566

130

Obsolete. Honeywell logo; used with Q674L1538 and
C815A1005; used in Y594R1375.

Y594R1763a

Description

Remarks

See subbase description for
replacement information.

Wiring differences (old=new):
W1=W, E=X2, X=F, C=B.

Wiring differences (old=new):
W1=W, E=X2, X=F, C=B.

a

Both the thermostat and subbase must be replaced.

67

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

R1574

132

R1582

Trade Model
Replacement

Description

Remarks

Obsolete. Comfortmaker logo; part no. 1505739; used
with Q674L1538; used in Y594R1383.

a

Y594R1243

Wiring differences (old=new):
C=X, X=L, W=W2.

132

Obsolete. Arcoaire logo; part no. 150739; used with
Q674L1538; used in Y594R1391.

Y594R1243a

Wiring differences (old=new):
C=X, X=L, W=W2.

R1590

115

Obsolete. Refac logo; used with Q674L1207.

T874R1152/
Y594R1243a

Replacement has °F
scaleplate.

R1608

119

Obsolete. Honeywell logo; Intertherm heat pump; used
with Q674L1264; used in Y594R1409.

Y594R1763a

Wiring differences (old=new):
W2=W, X=B, Z=F, K=X2,
W1=O.

R1616

168

Honeywell logo; SUPER TRADELINE® model; used
with Q674L1587; used in Y594R1425.

Y594R1425a

R1624

200

Obsolete. Honeywell logo; used with Q674L1595; used
in Y594R1433.

Y594R1243a

R1632

134

Obsolete. Honeywell logo; used with Q674L1603.

Y594R1243a

R1640

115

Obsolete. Hitecsa logo; °C scaleplate; H2 anticipator
factory set at 1.2A; used with Q674L1207.

Y594R1243a

R1657

136

Obsolete. American Standard logo; part no.
ASYSTAT651; requires outdoor reset; used with
Q674L1611; used in Y594R1441.

Y594R1763a

R1673

108

Heil logo; part no. 1060321, HAXB004TW01; used with
Q674L1132; used in Y594R1466.

Y594R1292a

R1699

119

Obsolete. Miller logo; used with Q674L1264; used in
Y594R1482.

Y594R1763a

R1707

209

Trol-A-Temp by Honeywell logo; Premier White® color;
used with Q674L1678; used in Y594R1490.

None

See Trol-A-Temp for
replacement.

R1715

209

Trol-A-Temp by Honeywell logo; used with Q674L1186;
used in Y594R1508.

None

See Trol-A-Temp for
replacement.

R1723

218

Obsolete. No logo; Snyder General part no. 654958B07;
°F/°C scaleplate; used with Q674L1702 and
C815A1005; used in Y594R1516.

Y594R1672a

R1731

108

Obsolete. Inter-City Products logo; part no.
HQ11477909HW; used with Q674L1132; used in
Y594R1524.

Y594R1292a

R1749

108

Tempstar logo; part no. 1060322, TAXB004TW01; used
with Q674L1132; used in Y594R1532.

Y594R1292a

R1814

108

Obsolete. Honeywell logo; Keeprite part no. THPC; °C
scaleplate; used with Q674L1132; used in Y594R1607.

Y594R1292a

R1822

230

Honeywell logo; TRADELINE model; used with
Q674L1710; used in Y594R1615.

Y594R1615a

R1830

134

Obsolete. Addison logo; WeatherKing part no. 4120796-61; used with Q674L1504; used in Y594R1656.

Y594R1300a

R1855

228

Obsolete. Lennox logo; Premier White® color; °C
scaleplate; outdoor reset required (use C815A1005);
used with Q674L1728; used in Y594R1714.

Y594R1763a

R1871

120

Honeywell logo; designed to replace Y594R1011 (York
part no. 2TH11702224); used with Q674L1736; used in
Y594R1664.

Y594R1664a

a

Both the thermostat and subbase must be replaced.

60-2485—8

68

Wiring differences (old=new):
X=B, Z=F, W2=W, K=X2,
W1=O.
Replacement has °F
scaleplate.

Wiring differences (old=new):
W2=W, X=B, Z=F, K=X2,
W1=O.

Wiring differences (old=new):
W1=W, X=X2, C=B.

Replacement has °F
scaleplate.

Wiring differences (old=new):
Y1=Y, L=F, W1=W, E=X2,
C=B; replacement has °F
scaleplate.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

R1889

120

Honeywell logo; designed to replace Y594R1151 (York
part no. 2TH11702324), Y594R1193 (York part no.
6TH11702224), and York part no. 2TH11704024; used
with Q674L1736 and C815A1054; used in Y594R1672.

Y594R1672

R1897

230

Honeywell logo; Premier White® color; used with
Q674L1751; used in Y594R1680.

Y594R1680a

R1905

120

Obsolete. Honeywell logo; Premier White® color;
designed to replace Y594R1151 (York part no.
2TH11702324), Y594R1193 (York part no.
6TH11702224), and York part no. 2TH11704024; used
with Q674L1777 and C815A1054; used in Y594R1698.

Y594R1672a

Replacement is beige.

R1913

120

Obsolete. Honeywell logo; Premier White® color;
designed to replace Y594R1011 (York part no.
2TH11702224); used with Q674L1777; used in
Y594R1706.

Y594R1664a

Replacement is beige.

R1921

115

Obsolete. Econar logo; used with Q674L1207; used in
Y594R1722.

Y594R1243a

R1939

197

American Standard logo (Trane); part no.
ASYSTAT651A; includes outdoor reset; used with
Q7674L1801; used in Y594R1748.

Y594R1763a

R1947

168

Obsolete. Inter-City Products logo; part no.
HQ1149406HW; used with Q674L1819; used in
Y594R1755.

Y594R1425a

R1954

197

Honeywell logo; TRADELINE model; includes outdoor
reset; used with Q674L1827; used in Y594R1763.

Y594R1763a

Direct replacement for
Y594R1748 (T874R1939/
Q674L1801) American
Standard logo (ASYSTAT
651A) and Y594R1136
(T874R1053/Q674L1140).

R1962

115

Obsolete. Consolidated Industries logo; part no.
9036100; Premier White® color; used with Q674L1843;
used in Y594R1771.

Y594R1680a

Includes CHECK LED.

R1970

120

York logo; Canada; Premier White® color; °C scaleplate;
used in Y594R1789; used with C815A1039.

Y594R1672a

Replacement has °F
scaleplate.

R1988

125

Honeywell logo; TRADELINE model; used with
Q674L1868; used in Y594R1797.

Y594R1797

Direct replacement for
Y594R1235 (T874R1368/
Q674L1421) Evcon/Coleman
part no. 3600-368.

R2002

245

Obsolete. Amana Air Conditioning logo; part no.
10574102; used in Y594R1805.

Y594R1797

Wiring differences (old=new):
C/X=X.

R2010

245

Obsolete. Amana Air Conditioning logo; part no.
10574104.

Y594R1797

Wiring differences (old=new):
C/X=X, W3=W2.

R2028

209

Obsolete. York logo; part no. 2TH11703424A; used with
Q674L1918 in Y594R1821.

Y594R1797

R2036

134

Ruud logo; °C scaleplate; used with Q674L1504.

See OEM for
replacement.

T874S
S1001

Remarks

a

2-stage heat, 3-stage cool.
223

T874V
V1008

Trade Model
Replacement

Description

Obsolete. Carrier Synergy 2000 Heat Pump System
Control logo; used with Q674F1501.

T8611M2025 Includes night setback.
(programmable)
or see OEM for
direct
replacement.

1-stage cool.
69

Obsolete. No logo; Carrier part no. HH07AT177; used
with Q674R1003.

T874A1036

a

Both the thermostat and subbase must be replaced.
69

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 8. T874 Cross Reference.
Model
Number

Fig.
No.

T874W

Trade Model
Replacement

Description

Remarks

3-stage heat, 2-stage cool, manual changeover.

W1007

118

Obsolete. Honeywell logo; Westinghouse special; used
with Q674L1256.

W1015

54

Honeywell logo; used with Q674B1216 and C815A1005;
used in Y594W1014.

T874W1015

W1023

233

Obsolete. Lennox Advanced Heat Pump System logo;
used with Q674L1280 and W89.

T874W1015

W1031

140

T8611M2025 Includes night setback.
Obsolete. No logo; Rheem part no. 41-20797-20; used
with Q674L1546 and C815A1005; used in Y594W1022. (programmable)

W1049

100

Obsolete. McQuay logo; part no. 61202501; 12°F
interstage differential between H2 and H3 for night
setback; used with Q674C1363.

W1056

220

Obsolete. McQuay/Snyder General logo; part no.
1202501; 12°F differential between H2 and H3 for night
setback; used with Q674C1363 (61202502).

See OEM for
replacement.

W1064

220

Obsolete. AAF/Snyder General logo; part no.
066804408; 12°F differential between H2 and H3 for
night setback; used with Q674C1363 (66804408).

See OEM for
replacement.

W1072

140

Obsolete. Honeywell logo (Inter-City Products); used in
Y594W1030.

W1080

220

McQuay logo; part no. 073318901; Premier White®
color; 12°F differential between H2 and H3 for night
setback.

W1106

247

Obsolete. Addison logo; part no. 843-277; °F/°C
scaleplate; used with Q674L1934 in Y594W1055.

T874Y

T8611M2025 Includes night setback.
(programmable)

T8611M2025 Includes night setback.
(programmable)

T8611M2025 Includes night setback.
(programmable)
None

T8611M2025

Heat pump model; 2-stage heat, 2-stage cool, heat or
cool auto changeover.

Y1005

210

Obsolete. Mammoth Water Source Heat Pump logo;
used with Q674E1353; used in Y594Y1004.

See OEM for
replacement.

Y1013

248

Obsolete. WaterFurnace logo; part no. TA21H03;
Premier White® color; °F/°C scaleplate; used with
Q674F1675 (32003081).

See OEM for
replacement.

a

Both the thermostat and subbase must be replaced.

60-2485—8

70

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

Q674A

Q674 Trade
Replacement

Description

Remarks

System: HEAT-AUTO-COOL; Fan: AUTO-ON

A1001

71

Standard OEM.

Q674A1019

A1019

71

TRADELINE® model; used with T874A-D.

Q674A1019

A1035

71

Obsolete. Trane part no. BAS-0435; used with T874A-D.

Q674A1019

A1043

71

Honeywell logo; TRADELINE model;

Q674A1019

A1050

71

Obsolete. Standard OEM.

Q674A1043

Q674B

System: HEAT-OFF-COOL; Fan: AUTO-ON

B1000

45

Standard OEM; used with T874C1570, C1695, C1703,
D1843; used in Y594C1363.

Q674B1034

B1018

44

Standard OEM; used with T874B1035, D1082; used in
Y594B1026, D1016.

Q674B1018

B1026

45

Obsolete. System: HEAT-OFF-RESET-COOL.

Q674B1034

B1034

45

TRADELINE

Q674B1034

B1042

47

Obsolete. Used with T874R1004, R1509; used in
Y594R1029, R1334.

Y594R1243a

Wiring differences (old=new):
W1=W2.

B1059

45

Obsolete. Factory installed RC-RH jumper; used with
T874C1059; used in Y594C1256.

Q674B1034

Field wire RC-RH.

B1075

46

Auto fan in heating and cooling mode; used with
T874B1035, C1000, D1082; used in Y594D1040.

Q674B1075

B1083

51

Obsolete. Carrier part no. HH93AZ178; factory
installed RC-RH jumper.

Q674B1075a

B1091

45

Obsolete. Carrier part no. HH93AZ184; factory
installed RC-RH jumper.

Q674B1034

B1109

47

Obsolete. Addison heat pump; used with T874R1012.

Y594R1243a

B1117

44

Obsolete. Carrier part no. HH93AZ180; factory
installed RC-RH jumper.

Q674B1018a

B1125

53

Obsolete. York part no. 2TB04700324A; used with
T874D1041.

Q674B1075a

B1133

48

Obsolete. Includes FILTER LED; used with
T874D1082; used in Y594D1156.

Q674B1018

B1141

51

Trane part no. BAY28X185; automatic fan operation in
heat and cool mode.

Q674B1075

Set T874 H1 anticipator for
combined load of heat relay
and fan relay.

B1158

50

Obsolete. Used with T874G1071.

T874C1018/
Q674B1018a

W1-Y1 and RH-RC jumpers
required.

B1166

249

Carrier part no. HH93AZ179; factory installed RC-RH
jumper; LOCKOUT LED; used with T874C1075
(HH07AT170).

Y594C1421 or Replacement only requires
Q674B1075a one transformer and has no
LOCKOUT LED.

B1190

52

Obsolete. Wards special; factory installed RH-RC and
F-W3 jumpers; used with T874C1372.

Gas Furnace:
Q674B1034

One system transformer only.

Wiring differences (old=new):
W1=W2.

Jumper RC-RH; replacement
has no LOCKOUT LED.

Electric Furnace:
Q674B1075

a

B1208

187

Obsolete. Used with T874C1422.

B1216

54

Used with T874W1015 and C815A1005; used in
Y594W1014.

Q674B1216

None

B1224

49

Obsolete. Lennox part no. 25F7301; four LEDs; used
with T874C1430.

Q674B1034

Replacement has no LEDs.

Both the thermostat and subbase must be replaced.

71

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

Q674 Trade
Replacement

B1240

234

Obsolete. Northrup heat pump; AUX HEAT LED; used
with T874G1139.

Y594G1252

B1257

56

Obsolete. LSI-Mammoth; RESET LED; automatic fan
operation in heat and cool modes; used with
T874C1471; used in Y594C1314.

Q674B1075

Replacement has no LED.

B1273

57

Obsolete. McQuay part no. 860-442727B-00; System:
OVERRIDE-HEAT-OFF-COOL; used with T874P1006.

T874A1036/
Q674B1075a

Wiring differences (old=new):
Y=Y1, L=R, W=O; jumper Y1W1; no night setback.

Description

a

Remarks
Wiring differences (old=new):
Y1=Y2, W1=W2; EM HT
system switch position is not
operational.

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.

a

See OEM for
replacement.

B1281

191

Obsolete. Carrier no. 42QH400103; System: HEATOFF-COOL; Fan: LOW-HI-CONT; international
symbols on switches; used with T874R1319.

B1299

46

Obsolete. Heil Quaker part no. HQ521714HW.

Q674B1075

B1307

62

Obsolete. Includes two LEDs; used with T874F1122.

T874F1015/
Q674D1040a

B1315

68

Obsolete. Friedrich part no. AQ5215; OVERRIDE and
SERVICE LEDs; used with T874P1022, P1030.

B1331

65

Obsolete. Includes two LEDs; used with T874A1002.

B1349

67

Obsolete. Goettl part no. 372072; used with
T874R1541.

Y594R1300

B1356

138

Obsolete. Carrier part no. HH93AZ192; used with
T874L1018 (HH07AT178).

See OEM for
replacement.

B1372

44

Obsolete. Trane part no. BAS-0427; used with T874A-D.

Q674B1018

B1380

46

Obsolete. Trane part no. BAS-0426; used with T874A-D.

Q674B1075

B1398

48

Obsolete. Trane part no. BAS-0431; FILTER LED;
used with T874A-D.

Q674B1034

Replacement has no LEDs.

B1406

172

Obsolete. Carrier part no. HH93AZ200; FAULT and
CHECK FILTER LEDs; used with T874H1070
(HH07AT166), T874H1088 (HH07AT167) or
T874H1153 (HH07AT167); used in Y594H1046.

T874A1150/
Q674B1075a

Wiring differences (old=new):
Y=Y1; jumper W1-Y1;
replacement has no LEDs.

B1414

51

American Standard (Trane) part no. ASYSTAT1617.

Q674B1075

B1448

215

Obsolete. Carrier part no. HH93A2202; Fan: Lo-MedHigh-On; used with T874L1059.

See OEM for
replacement.

B1455

214

Obsolete. Carrier part no. HH93AZ208; Fan: Lo-MedHigh-On; used with T874A1424 (HH07AT194).

See OEM for
replacement.

B1463

45

Trol-A-Temp; used with T874D1801.

B1471

45

Trol-A-Temp; used with T874D1827.

B1513

53

Obsolete. TRADELINE; exact replacement for
Q674B1125 (York part no. 2TB04700324).

Q674B1075

Jumper RC-RH; replacement
has no LOCKOUT LED.

B1521

53

Obsolete. Carrier Canada part no. HH93AZ179-W;
gray color; includes LOCKOUT LED and removable
jumpers between RC and RH terminals.

Q674B1075

Jumper RC-RH; replacement
has no LOCKOUT LED; beige
color.

B1539

45

Obsolete. Carrier part no. HH93AZ139; used with
T874D2049; used in Y594D1370.

Q674B1034

B1547

237

Obsolete. TRADELINE; gray color; used with
T874C1810; used in Y594C1389.

Y594C1389

Both the thermostat and subbase must be replaced.

60-2485—8

72

Replacement has no LEDs.

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; set dual fuel switch
to electric heat; night setback.
Q674B1034

Replacement has no LEDs.

a

None

See Trol-A-Temp.

None

See Trol-A-Temp.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

B1554

82

Obsolete. TRADELINE; includes LOCKOUT LED and
removable jumpers between RC and RH terminals;
used with T874C1877; used in Y594C1421.

Y594D1347

B1562

45

Obsolete. Amana logo; part no. P1217701F;
removable jumpers between RC and RH terminals.

Q674B1034

B1570

45

Obsolete. Armstrong logo; part no. 03299A18.

Q674B1034

Replacement is beige.

B1588

45

Obsolete. Standard OEM.

Q674B1034

Replacement is beige.

Q674C
C1009

Q674 Trade
Replacement

Description

Remarks
Jumper RH-RC; system
switch: Off-HEAT-AUTOCOOL.

System: OFF-AUTO; Fan: AUTO-ON
72

C1017

Standard OEM; used with T874D1082; used in
Y594D1024.

Q674C1058

Obsolete. Includes factory-installed RC-RH jumper;
used with T874A,F,Q.

Q674C1058

C1033

72

Trane part no. BAY28X187.

Q674C1058

C1041

74

Obsolete. Command Aire heat pump; used with
T874H1005, H1054.

Y594H1012a

C1058

72

TRADELINE

Q674C1058

C1066

73

Obsolete. Command Aire heat pump; used with
T874G1352.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; W-Y jumper
required.
Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none; RL jumper required; no night
setback.

T8600D2028 Wiring differences (old=new):
(programmable) Y1=O, Y2=Y, L=R; W-Y
jumper required; night
setback.

a

C1074

81

Obsolete. Used with T874C1018.

C1090

77

C1108

Q674C1058

Jumper W2-Y1 and RH-RC.

Obsolete. LSI-Mammoth heat pump; used with
T874K1001.

Y594R1419

a

Wiring differences (old=new):
RH-RC=R, W1=B, W3=W2,
W2=W1; remove Y1-W1
jumper.

143

Obsolete. Northrup special; AUX HEAT LED; used with
T874G1139.

Y594R1243a

Wiring differences (old=new):
Y1=Y, W1=W2, C=X.

C1116

76

Obsolete. McQuay part no. 02005959; two LEDs; used
with T874D1116.

Q674C1058

Replacement has no LEDs.

C1124

79

Obsolete. LSI-Mammoth heat pump; RESET LED;
used with T874G-H; used in Y594G-H.

Y594G1294
T8600D2028

C1132

75

Obsolete. McQuay part no. 03005049; spring return
momentary system switch position; used with
T874A1283.

See OEM for
replacement.

C1140

78

Obsolete. McQuay no. 860-442728B-00; System:
OVERRIDE-AUTO-OFF; used with T874P1006.

C1157

72

Obsolete. York part no. 2TB04700124A.

Q674C1058

C1165

192

Obsolete. McQuay part no. 03005050; spring return
momentary system switch position.

See OEM for
replacement.

C1173

96

Obsolete. American Air Filter part no. 4ELN-8787;
used with T874C1133.

Q674C1058

C1181

76

Obsolete. California heat pump; used with T874C1000.

Q674C1058

C1199

163

Obsolete. American Air Filter part no. 4ELN-8788; two
LEDs; spring return momentary system switch position;
used with T874G1485, G1535.

T8600D2028

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.

Replacement has no LEDs.

No momentary reset switch.

Both the thermostat and subbase must be replaced.

73

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

Q674 Trade
Replacement

C1207

78

Obsolete. Friedrich; System: OVERRIDE-AUTO-OFF;
used with T874P1014.

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.

C1215

97

Obsolete. Friedrich part no. AQ5315; System:
OVERRIDE-AUTO-OFF; OVERRIDE and SERVICE
LEDs; used with T874P1022, P1030.

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.

C1223

73

Obsolete. Friedrich part no. AQ5323; used on systems
requiring night setback contacts; used with
T874G1584.

Description

Y594H1012a

Remarks

Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none; RL jumper required; no night
setback.

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.
C1249

164

Includes MALFUNCTION LED; used with T874H1062;
used in Y594H1012.

Y594H1012a

C1256

73

Obsolete. Used with T874G1618.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none; RL jumper required; no night
setback.

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.
C1264

165

Obsolete. Carrier part no. HH93AZ193; used with
T874L1018 (HH07AT178).

See OEM for
replacement.

C1280

181,
203

Obsolete. McQuay heat pump; part no. 60687401;
COMP FAULT LED; used with T874K1019, L1034.

T8600D2028

C1298

76,
225

Obsolete. McQuay part no. 60684801; SERVICE LED;
used with T874A1523, A1549, D1918.

See OEM for
replacement.

C1306

75

Obsolete. McQuay part no. 60685001; SERVICE LED;
spring return momentary system switch position; used
with T874A1325.

See OEM for
replacement.

C1314

72

Obsolete. Trane part no. BAS-0429; used with T874A-F.

Q674C1058

C1322

173

Obsolete. Carrier part no. HH93AZ199; FAULT and CK
FILTER LEDs; used with T874H1070 (HH07AT166),
T874H1088 (HH07AT167) or T874H1153
(HH07AT167); used in Y594H1053.

Y594H1012a

Wiring differences (old=new):
2=X.

C1330

177

Obsolete. LSI-Mammoth part no. 71115201; RESET
LED; used on systems with night setback contacts;
used with T874G1659, H1096; used in Y594G1427,
H1020.

Y594H1012a

Wiring differences (old=new):
R1=R; R2=L.

C1355

74

Friedrich part no. AQ355; SERVICE LED; used with
T874H1112.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required.

C1363

99

Obsolete. McQuay part no. 61202601; SERVICE LED;
auto fan in heat and cool mode; used with T874C.

T874C1125/
Q674B1075a

Replacement has HEAT-OFFCOOL.

219

Obsolete. Used with T874C.

See OEM for
replacement.

220

Obsolete. Used with T874W.

See OEM for
replacement.

100

Obsolete. Used with T874W.

72

American Standard part no. ASYSTAT616.

C1371
a

T8611M2025 Includes night setback.
(programmable)

Both the thermostat and subbase must be replaced.

60-2485—8

See thermostat description for
replacement information.

74

Q674C1058

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

Q674 Trade
Replacement

C1389

205,
176

Obsolete. Command Aire part no. P1099-0021; two
LEDs; used with T874G-H.

None

See thermostat description for
replacement information.

C1397

205,
171

Obsolete. Command Aire part no. P1099-0023; used
with T874G-H.

None

See thermostat description for
replacement information.

C1413

213

Obsolete. Carrier part no. HH93AZ204; Fan: Lo-MedHigh-On; used with T874L1059.

See OEM for
replacement.

C1439

217

Obsolete. Bard part no. 8404-016; used with
T874N1024.

See OEM for
replacement.

C1454

163

Obsolete. Climate Master part no. AQ5354; two LEDs;
spring return momentary system switch position.

Y594G1393a

C1462

25

Climate Master Special.

Q674C1058

Replacement has no LEDs.

C1470

221

Obsolete. Climate Master part no. RQ5370; used with
T874H1138.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; replacement has
MALFUNCTION LED only.

C1496

74

Obsolete. Carrier part no. HH93AZ213; includes
SERVICE LED; used with T874H1161; used in
Y594H1038.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y; L-R jumper
required.

C1504

83

Obsolete. Carrier part no. HH93AZ214; used in Y594.

Y594H1012a

Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none; RL jumper required; no night
setback.

Description

Remarks

No momentary reset switch.

T8600D2028 Wiring differences (old=new):
(programmable) Y1=O, Y2=Y, L=R; W-Y
jumper required; night
setback.
C1512

97

Obsolete. Carrier part no. HH93AZ216; System:
Override-Auto-Off; includes two LEDs; used in Y594.

C1520

72

Obsolete. Carrier part no. HH93AZ210; used with
T874D2049; used in Y594D1388.

Q674C1058

C1538

163

Climate Master part no. AQ5354; System: Off-AutoOverride; includes two LEDs and momentary spring
position.

Y594G1393

No momentary reset switch.

C1546

76,
225

Obsolete. McQuay part no. 060684802; gray color;
includes one LED.

Q674C1058

Replacement has no LEDs;
beige color

C1553

181,
203

Obsolete. McQuay logo; part no. 073319901; includes
one LED.

Q674C1058

Replacement is beige.

C1561

76

McQuay logo; part no. 073319701; includes one LED.

See OEM for
replacement.

C1579

99,
100

McQuay logo; part no. 073320001; includes one LED.

See OEM for
replacement.

C1595

72

Obsolete. Standard OEM.

Q674C1058

Q674D
D1008

System: None; Fan: None
55, 66 Obsolete. Used with T874D1082, F1056; used in
Y594D1057.

Q674D1040

D1016

55

Obsolete. Carrier part no. HH93AZ170; RC-RH jumper.

Q674D1040

RC-RH jumper required.

D1032

58

Obsolete. Borg-Warner; used with T874G.

T874D1165/
Q674D1040a

Wiring differences (old=new):
Y=Y2, O=Y1, W=W2; jumper
W1-Y2 required.

D1040

55

TRADELINE

Q674D1040

D1057
a

T8600D2028 Wiring differences (old=new):
(programmable) L=R, W=O; W-Y jumper
required; night setback.

55, 66 Obsolete. York part no. 2TB04700424A.

Q674D1040

Both the thermostat and subbase must be replaced.

75

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

D1065

63

Obsolete. Includes two LEDs; used with T874F1122.

T874F1015/
Q674D1040a

D1099

55, 66 Obsolete. Trane part no. BAS-0430; used with T874A-F.

Q674D1040

D1107

55, 66 Obsolete. Snyder General part nos. 654958801/
1520503/ 4ELN30070.

Q674F1040.

D1115

208

Trol-A-Temp; used with T874D1801.

D1123

208

Trol-A-Temp; gray color; used with T874D1827.

D1156

55

Obsolete. Gray color; includes removable jumper
between RC and RH terminals.

Q674D1040

D1164

66

Obsolete. Carrier part no. HH93AZ211; used in
Y594D1440.

Q674D1040

D1172

208

Obsolete. Amana logo; part no. P121501F; removable
jumpers between RC and RH terminals.

Q674D1040

D1180

55

Obsolete. York logo; part no. 2TH04703224A.

Q674D1040

D1198

55, 66 Obsolete. Standard OEM.

Q674E

a

Q674 Trade
Replacement

Description

Remarks
Replacement has no LEDs.

None

See Trol-A-Temp.

None

See Trol-A-Temp.

T874D1165/
Q674D1040

Replacement is beige color.

Replacement is beige color.

System: OFF-HEAT-AUTO-COOL; Fan: AUTO-ON

E1007

82

Used with T874D1504; used in Y594D1180.

Q674E1049

E1015

84

Obsolete. Lennox heat pump; used with T874G1006,
G1154.

Y594G1252a

E1049

193

TRADELINE; used with T874D2031 and TG504A1025;
used in Y594D1354.

Q674E1049

E1056

82

Obsolete. Amana part no. D68535-7; used with
T874C1059, C1331; used in Y594C1009.

Q674E1049

E1064

83

Obsolete. RC-RH jumpered internally; EM HEAT LED.

Q674E1049

E1072

82

Carrier part no. HH93AZ176; RC-RH jumpered
internally.

Q674E1049

E1080

82

Trane part no. BAY28X184.

Q674E1049

E1098

85

Obsolete. Used with T874A-D.

Q674E1049

E1106

185

Obsolete. ITT Nesbitt.

See OEM for
replacement.

E1114

87

Carrier part no. HH93AZ177; RC-RH jumper;
LOCKOUT LED to indicate compressor lockout; used
with HH07AT series thermostats.

Q674E1049

RC-RH jumper required;
replacement has no LED.

E1122

83

Obsolete. Square D part no. 63600-002-10; CHECK
LED.

Q674E1049

Replacement has no LED.

E1148

86

Obsolete. Lennox heat pump; used with T874G1014,
G1022.

Y594G1252a

Wiring differences (old=new):
R=O, M=Y, F=G, Y=W2,
V-VR=R; must use single
transformer.

E1155

88

Obsolete. Lennox part no. 91C7501; HIGH and LOW
LEDs; used with T874B1076, D1017.

Q674E1049

Replacement has no LEDs.

E1197

89

Obsolete. McQuay part no. 02005961; two LEDs; used
with T874D1116.

Q674E1049

Wiring differences (old=new):
D=O; replacement has no
LEDs.

E1205

80

Obsolete. Fedders special; SERVICE LED; used with
T874D1462.

Q674E1049

Replacement has no LEDs.

E1213

82

York part no. 2TB04700224A.

Q674E1403

E1221

82

Heil Quaker part no. HQ712003HW.

Q674E1049

Both the thermostat and subbase must be replaced.

60-2485—8

76

Wiring differences (old=new):
R=O, M=Y, F=G, V=R, Y=W2;
E-W2 jumper required.

RC-RH jumper required.

RC-RH jumper required.

RC-RH jumper required.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

Remarks

E1262

82

Lennox part no. 13F1701.

Q674E1049

E1270

198

Obsolete. Carrier part no. HH93AZ189; used with
T874L1000 (HH07AT176).

Y594G1419a

E-W2 jumper required.

E1304

82

Obsolete. BDP part no. P272-1887; used with
T874L1026.

Y594G1419a

E-W2 jumper required.

E1312

224

Obsolete. McQuay part no. 60684901; one LED; used
with T874A1523, A1549, D1686, D1918.

Q674E1049

Replacement has no LEDs.

E1320

82

Obsolete. Trane part no. BAS-0434.

Q674E1049

E1338

88

Obsolete. Goodman part no. CHTS36-60; HIGH and
LOW LEDs; used with T874B1100; used in
Y594B1042.

Q674E1049

E1346

82

Obsolete. Snyder General part nos. 1505753/1506753/
654958B02; used with T874D1769; used in
Y594D1297.

Q674E1049

E1353

210

Obsolete. Mammoth; used with T874Y1005; used in
Y594Y1004.

T8611M2025

Replacement has no LEDs.

E1379

212

Trol-A-Temp by Honeywell; used with T874A1465.

None

E1395

222

Obsolete. Carrier part no. HH93AZ209; used with
T874B1134 (HH07AT199).

T874B1019/
Q674E1049a

E1403

82

TRADELINE; designed to replace York 2TH04701024;
used with T874D1942; used in Y594D1347.

Y594D1347a

E1411

82

Obsolete. Carrier Canada part no. HH93AZ176-W;
gray color; removable jumper between RC and RH
terminals.

Q674E1049

RC-RH jumper required.
Replacement is beige color.

E1429

87

Carrier Canada part no. HH93AZ177-W; gray color;
includes LOCKOUT LED; removable jumper between
RC and RH terminals.

Q674E1049

RC-RH jumper required.
Replacement has no LOCKOUT LED and is beige color.

E1445

82

Obsolete. Carrier part no. HH93AZ217-W; gray color;
removable jumper between RC and RH terminals.

Q674E1049

RC-RH jumper required.
Replacement is beige color.

E1460

224

McQuay logo; part no. 073319801; includes one LED.

E1478

82

Obsolete. Armstrong logo; part no. 03299A19.

Q674E1049

RC-R jumper required.
Replacement is beige color.

E1486

82

Obsolete. Standard OEM.

Q674E1049

RC-R jumper required.
Replacement is beige color.

Jumper E-X2.

Q674F

a

Q674 Trade
Replacement

Description

See Trol-A-Temp.
Wiring differences (old=new):
W1 =W; RC-RH jumper
required; replacement has no
LEDs.

System: EM.HT.-HEAT-AUTO-COOL-OFF;
Fan: AUTO-ON

F1006

141

Obsolete. Includes EM HEAT LED; used with
T874C1331.

Q674F1022

F1022

142

Includes LED and field selectable inserts; used with
T874C1059; used in Y594C1017, C1330.

Q674F1022

F1030

146

Carrier part no. HH93AZ174; SUPL HEAT LED; used
with T874D1074 (HH07AT172).

Q674F1022

Wiring differences (old=new):
C=X1, X=X2.

F1048

149

Obsolete. Includes EM HEAT LED and auxiliary power
terminal Z.

Q674F1022

Replacement does not include
Z terminal and only requires
one transformer.

F1063

146

Obsolete. Carrier part no. HH93AZ181; SUPL HEAT
LED; used with T874D1074 (HH07AT172).

Q674F1022

Wiring differences (old=new):
C=X1, X=X2.

F1071

142

Obsolete. Square D part no. 63600-002-11; CHECK
LED.

Q674F1022

Both the thermostat and subbase must be replaced.

77

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.

a

Model
Number

Fig.
No.

F1089

152

Q674 Trade
Replacement

Description
Obsolete. Includes EM HEAT LED; X2-E and RC-RH
jumpers.

Remarks

Q674F1022

F1097

142

Obsolete. Southwest special; W2-X2 jumper.

Q674F1022

F1105

145

Obsolete. Lennox heat pump; EM HEAT LED; used
with T874G1154.

Y594G1252a

Wiring differences (old=new):
V=R, Y=W2, F=G, X2=X,
R=O, M=Y; L-E jumper
required.

F1113

150

Obsolete. Lennox heat pump; part no. 24F6201; V-VR
jumper; EM HEAT LED; changeover in cooling; used
with T874G1014, G1022.

Y59461252a

Wiring differences (old=new):
R=O, M=Y, F=G, Y=WC,
V=VR=R; must use single
transformer.

F1121

153

Obsolete. Westinghouse heat pump; EM HEAT LED;
used with T874G1048.

Y594G1252a

F1139

148

Obsolete. Tappan heat pump; EM HEAT LED; auto fan
in emergency heat mode; used with T874G1147.

Y594G1252a

F1162

151

Obsolete. Crispaire heat pump; EM HEAT LED; used
with T874G.

Y594G1393a

F1170

153

Obsolete. Heatwave (Southwest Mfg.) heat pump; EM
HT LED; used with T874G1105.

Y594G1252a

F1188

153

Obsolete. Luxaire heat pump.

Y594G1252a

F1196

178

Obsolete. Williamson; EM HEAT and SERVICE LEDs;
used with T874N1008; used in Y594N1007.

Q674F1220

F1204

154

Obsolete. Special for Crispaire; EM HEAT and COMP
FAULT LEDs; used with T874G1089; used in
Y594G1153.

Y594G1393a

F1212

155

Includes AUX HEAT and EM HEAT LEDs; used with
T874G1246, G1451, G1592, G1915; used in
Y594G1252.

F1220

178

Used with T874N1016; used in Y594N.

Q674F1220

F1238

155

Obsolete. Rheem part no. 41-20797-14; AUX HEAT
and EM HEAT LEDs; used with T874G1097, G1212,
G1220, G1238.

Y594G1252a

F1246

156

Obsolete. Westinghouse heat pump; EM HEAT and
AUX HEAT LEDs; auto fan in emergency heat mode;
changeover in cooling mode.

Y594G1252a

F1253

157

Obsolete. Wesco/Addison heat pump; used with
T874G1261, G1279, G1287.

Y594G1252a

Wiring differences (old=new):
Y1=O, C=X, W1=Y, X=L.

F1261

179

Includes two LEDs; used with T874N1024; used in
Y594N.

Y594G1419a

Wiring differences (old=new):
L=X2, Y=Y1.

F1279

158

Obsolete. Westinghouse heat pump; two LEDs; used
with T874G.

Y594G1252a

Wiring differences (old=new):
L1=L.

F1295

147

Obsolete. Keeprite/Westinghouse heat pump;
SERVICE, AUX HEAT and EM HEAT LEDs; used with
T874G1188.

Y594G1252a

Wiring differences (old=new):
S=L; replacement does not
include A or T terminals.

F1311

155

York heat pump; AUX HEAT and EM HEAT LEDs; used
with T874G1410.

Y594G1252a

F1329

142

Obsolete. Heil Quaker part no. HQ712005HW; one
LED and field selectable inserts.

Q674F1022

F1337

166

Obsolete. WeatherKing heat pump; two LEDs and field
selectable inserts; used with T874D1009; used in
Y594D1222.

Q674F1022

Both the thermostat and subbase must be replaced.

60-2485—8

78

Wiring differences (old=new):
C=X.

Wiring differences (old=new):
A=L.

Q674F1212 or
Y594G1252a

Wiring differences (old=new):
R=RC-RH; replacement has
no LEDs.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.

a

Model
Number

Fig.
No.

Q674 Trade
Replacement

F1345

194

Obsolete. Addison heat pump; EM HEAT and CHECK
LEDs; used with T874G; used in Y594G.

Y594G1252

F1360

167

Obsolete. Rheem part no. 41-20797-17; AUX HEAT
and EM HEAT LEDs; used with T874G1493.

Y594G1526a

F1378

195

Obsolete. Includes EM HEAT and AUX HEAT LEDs;
used with T874G1501.

Y594G1252a

Wiring differences (old=new):
L1=L; changeover in cooling
only.

F1394

139

Obsolete. Nepco heat pump; HEAT PUMP and AUX
HEAT LEDs; System: AUX HEAT-HEAT PUMP-2
STAGE HEAT-OFF-COOL; used with T874D1595.

T874D1165/
Q674B1018a

Replacement has HEAT-OFFCOOL system switching and
no LEDs.

F1402

169

Obsolete. Coleman heat pump; two LEDs; used with
T874G1576; used in Y594G1377.

Y594G1633a

F1410

170

Used with T874G1246, G1915; used in Y594G1393.

Y594G1393a

F1428

199

Obsolete. Used with T874G1600; used in Y594G1401.

Y594G1419a

F1436

167

Includes AUX HEAT and EM HEAT LEDs; changeover
in heating mode; used with T874G1626; used in
Y594G1526.

None

F1444

227

Includes AUX HEAT, EM HEAT and CHECK LEDs;
used with T874G1642; used in Y594G1419.

Y594G1419a

F1451

204

Obsolete. York part no. 2TB047700524A; one LED and
field selectable inserts.

Q674F1012

F1477

227

TRADELINE; gray color; used with T874G1741,
G1824; used in Y594G1476, G1534.

Y594G1476a

F1485

211

Trol-A-Temp by Honeywell; changeover is provided by
Trol-A-Temp zone panel; used with T874G1758; used
in Y594G1492.

F1501

223

Obsolete. Carrier two-speed compressor heat pump;
used with T874S1001.

F1519

231

Obsolete. Nordyne; used with T874G1832, G1840;
used in Y594G1542, G1559.

Y594G1252a

Replacement has auto
changeover in cooling mode
only.

F1535

229

Obsolete. Lennox heat pump; gray color; used with
T874G1857; used in Y594G1583.

Y594G1161a

Wiring differences (old=new):
E=X2, C=B, L=F.

F1543

204

Obsolete. TRADELINE

Q674F1022

Wiring differences (old=new):
X2=X, X1=B.

F1550

243

Obsolete. Amana part no. 10573901; includes two
LEDs; used with T874G1899; used in Y594G1591.

Y594G1633

F1568

155

Obsolete. Gray color; includes two LEDs; used with
only T874G1931.

Y594G1476

F1584

169

TRADELINE; includes two LEDs; used with
T874G1972; used in Y594G1633. Direct replacement
for Coleman/Evcon Y594G1377 (T874G1576/
Q674D1402); Coleman part no. 3600-373.

Y594G1633a

F1592

238

Heat Controller; Fan: AUTO-ON; System: AUX HEATHEAT PUMP- 2 STAGE HEAT-OFF-COOL; includes
two LEDs; used with T874C1844; used in Y594C1413.

Y594R1425

E-W2 jumper required; system
switch: EM.HT.-HEAT-OFFCOOL.

F1600

169

Obsolete. Amana part no. 10573903; includes two
LEDs; used with T874G1980; used in Y594G1641.

Y594G1633

Wiring differences (old=new);
W3=W2.

F1634

139

Standard OEM; System: AUX HEAT-HEAT PUMP2 STG HEAT-OFF-COOL; includes two LEDs; used
with T874D2155.

Y594G1716

Description

a

None

Remarks
Wiring differences (old=new):
Y1=O, C=X, W1=Y, X=L.

Wiring differences (old=new):
jumper W1-Y1.

Wiring differences (old=new):
X2=X; X1=B.

See Trol-A-Temp.

T8611M2025 Includes night setback.
(programmable)

Y1-W1 jumper required.

Both the thermostat and subbase must be replaced.

79

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

F1667

155

WaterFurnace logo; part no. TA21H03; System: OFFAUTO-HEAT-EM HT; includes two LEDs; used with
T874G2046.

Y594G1716

F1675

248

Obsolete. WaterFurnace logo; part no. TA21H03;
includes four LEDs.

See OEM for
replacement.

Q674G

Remarks

System: OFF-AUTO; Fan: None

G1005

184

Obsolete. Used in Y594F1063.

Q674G1070

G1013

186

Obsolete. Climate Control; used with T874D1298.

See OEM for
replacement.

G1021

91

Obsolete. Includes O and B terminals; used with
T874A-F,Q or T874D1082; used in Y594D1032.

Q674G1070

G1047

92

Obsolete. Used with T874C1018, C1125.

G1054

188

Obsolete. Singer part no. 0200-5963; used with
T874D1298.

See OEM for
replacement.

G1062

232

Obsolete. Singer; used with T874D1298.

See OEM for
replacement.

G1070

91

TRADELINE

Q674G1070

G1088

92

Obsolete. LSI-Mammoth part no. 71120201; used with
T874C.

See OEM for
replacement.

G1096

90

Obsolete. Climate Control part no. 02005958; used
with T874D1439, D1447.

See OEM for
replacement.

G1104

94

Obsolete. McQuay part no. 0200-5963; two LEDs;
used with T874D1116.

See OEM for
replacement.

G1120

202,
226

Obsolete. McQuay part no. 60684701; two SERVICE
LEDs; no fan switching; used with T874D1694, G1926.

See OEM for
replacement.

G1138

91

Obsolete. Trane part no. BAS-0433; used with T874A-F.

Q674G1070

G1153

184

Obsolete. Carrier part no. HH93AZ212; used in
Y594D1396.

Q674G1070

T8611

G1161

184

Gray color.

Q674G1070

Replacement is beige color.

G1179

202

Obsolete. McQuay logo; part no. 073319601; includes
two LEDs.

Q674G1161

Replacement has no LEDs.

Q674J

a

Q674 Trade
Replacement

Description

System: EM.HT.-AUTO-OFF; Fan: AUTO-ON

J1001

180

Obsolete. Singer heat pump part no. 02005964; EM
HEAT LED; changeover heat mode.

See OEM for
replacement.

J1019

159

Obsolete. Westinghouse heat pump; EM HT LED;
System: EM.HT.-ON-OFF; used with T874G1048.

Y594G1252a

J1027

160

Obsolete. York part no. 025-22291; EM HEAT LED;
auto fan in emergency heat mode; changeover in cool
mode; used with T874G1170, G1196, G1428, G1345,
G1444; used in Y594G1013, G1138, G1229.

Y594G1567a

J1035

161

Carrier heat pump; part no. HH93AZ173; System:
SUPL.HT.-ON-OFF; SUPL HEAT LED; used with
T874G1055 (HH07AT171).

Y594G1674a

J1043

162

TRADELINE heat pump model; designed for use on
Trane heat pumps; AUX HT and EM HT LEDs; auto fan
in emergency heat; changeover in cooling mode; used
with T874G1204 and C815A1008; used in Y594G1161.

J1050

183

Obsolete. Westinghouse heat pump; EM HEAT and
AUX HEAT LEDs; used with T874G1071.

Both the thermostat and subbase must be replaced.

60-2485—8

80

Q674J1043 or
Y594G1161a

Y594G1674a

Wiring differences (old=new):
W=W2.

Designed for use on Trane
heat pumps.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.

a

Model
Number

Fig.
No.

Q674 Trade
Replacement

J1068

144

Obsolete. Carrier heat pump; part no. HH93AZ183;
used with T874J1002 (HH07AT175) or T874J1028
(HH07AT165).

Y594J1019

J1076

180

Obsolete. McQuay part no. 02005964; two LEDs; used
with T874A,D.

Q674F1022

Replacement has no LEDs.

J1084

171

Obsolete. BDP heat pump; part no. 34427DP126,
P272-1879; EM HEAT LED; used with T874J1010.

Y594J1019

Wiring differences (old=new):
W1=W2, F=L.

J1118

196

Obsolete. Carrier heat pump; part no. HH93AZ188;
SUPL HEAT LED; System: SUPL.HT.-ON-OFF; used
with T874G1055 (HH07AT171).

Y594G1674

Wiring differences (old=new):
C=X;Y1=W1; jumper required;
no auto fan in emergency
heat.

J1126

160

Obsolete. Luxaire no. 026-00068-000; EM HEAT LED;
used with T874G1568; used in Y594G1351.

Y594G1567a

J1142

174

Obsolete. American Standard part no. WY28X0250;
AUX HEAT and EM HEAT LEDs; used with
T874G1675; used in Y594G1443.

Y594G1161a

J1159

206

Obsolete. Carrier heat pump; part no. HH93AZ196;
used with T874J1002 (HH07AT175) or T874J1028
(HH07AT165).

Y594J1019

J1167

175

Obsolete. Carrier heat pump; MANUAL, AUTO, HEAT
PUMP and DEFROST LEDs; System: SUPL HEATON-OFF; used with T874G1717; used in Y507J1201.

Y594G1252a

Wiring differences (old=new):
C=X, D=L; replacement has
AUX HEAT and EM HEAT
LEDs.

J1175

216

Obsolete. Snyder General part nos. 1505756,
1506756; CHECK, AUX HEAT and SYSTEM LEDs;
used with T874G1774, G1782; used in Y594G1500,
G1518.

Y594G1252a

Wiring differences (old=new):
E=W2, W1=W3, X=E, C=X.

J1191

161

Obsolete. Carrier heat pump; gray color; used with
T874G1790.

Y594G1252a

Wiring differences (old=new):
C=X; replacement has °F
scaleplate.

J1209

160

TRADELINE; designed to replace Y594G1013 (York
part no. 2TH11702424), Y594G1229 (York part no.
6TH11702424) and York part no. 2TH11704124; used
with T874G1865; used in Y594G1567.

Y594G1567a

J1217

171

Obsolete. Nordyne part no. 9132250; used with
T874J1036, J1044.

J1225

160

Obsolete. TRADELINE; gray color; designed to replace
Y594G1013 (York part no. 2TH11702424), Y594G1229
(York part no. 6TH11702424) and York part no.
2TH11704124; used with T874G1873; used in
Y594G1575.

Y594G1567a

J1241

144

Obsolete. Carrier Canada part no. HH93AZ183-W;
gray color; System: SUPL HT-ON-OFF; includes one
LED.

See OEM for
replacement.

J1258

161

Obsolete. Carrier Canada part no. HH93AZ173-W;
gray color; System: SUPL HT-ON-OFF; includes one
LED.

Y594G1674a

J1266

160

York Canada; gray color; includes EM HT LED; used in
Y594G1625.

Y594G1567a

J1274

161

TRADELINE; System: SUPL HT-ON-OFF; includes
one LED; used with T874G2004; used in Y594G1674.

Y594G1674

J1282

244

Obsolete. TRADELINE; System: SUPL HT-ON-OFF;
includes SUPL HT LED; used with T874J1069; used in
Y594J1019.

(Recontrol)
T8511G1021

Description

Y594J1019

Remarks

Wiring differences (old=new):
F=L.
Replacement is beige.

Replacement is beige color.

Both the thermostat and subbase must be replaced.

81

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

Q674K

Remarks

System: OFF-HEAT-AUTO-COOL; Fan: None

K1000

93

Obsolete. Carrier part no. HH93AZ172; RC-RH jumper.

Q674E1049

K1018

95

Obsolete. Oneida Heater part no. 3040284-02;
System: OFF-WOOD-WOOD/OIL-OIL; used with
T874F1106.

Q674K1026

K1026

95

System: OFF-WOOD-WOOD/ OIL-OIL; used with
T874F1155.

Q674K1026

K1034

93

Obsolete. Snyder General part no. 4ELN-7920.

Q674E1049

Fan switch is not operational.

K1042

93

Obsolete. Carrier part no. HH93AZ172-W; gray color;
includes removable jumper between RC and RH
terminals.

Q674E1049

Fan switch is not operational.

Q674L

a

Q674 Trade
Replacement

Description

Fan switch is not operational.

System: EM.HT.-HEAT-OFF-COOL; Fan: ON-AUTO

L1017

101

Obsolete. York heat pump; EM HEAT LED; cooling
mode changeover; compressor lockout; auto fan in
EM.HT; used with T874R1046.

Y594R1243a

Wiring differences (old=new):
W=W2, X=L, B=X.

L1025

102

Obsolete. Lennox heat pump; part no. 24F6101; EM.
HEAT LED; V-VR jumper; used with T874R1020,
J1038.

Y594R1243a

Wiring differences (old=new):
M=Y, F=G, V-VR=VR, Y=W2,
R=O.

L1033

115

Obsolete. Rheem heat pump; EM HEAT LED; used
with T874R1152.

Y594R1243a

L1041

103

Obsolete. Carrier heat pump; part no. HH93AZ175;
SUPL HEAT LED; used with T874G1055
(HH07AT171), G1071 (HH93AZ175), G1113.

Y594G1419

Wiring differences (old=new):
C=X, jumper Y1=W1.

L1066

122

Obsolete. Fedders heat pump; used with T874R1269;
used in Y594R1037.

Y594R1615a

Wiring differences (old=new):
K=E, C=X, W1=B, Z=L.

L1074

124

Obsolete. Carrier heat pump; part no. HH93AZ186;
SUPL HT LED; used with T874J1002 (HH07AT175) or
T874J1028 (HH07AT165).

Y594J1001

L1082

104

Obsolete. Crispaire heat pump; W2-H jumper; EM
HEAT LED; used with T874R1061, R1111.

Y594R1243a

Replacement has auto fan in
emergency heat mode.

L1090

105

Obsolete. Fedders heat pump; EM HEAT LED;
changeover in heat mode; used with T874C1398,
C1406, C1414.

Y594R1425a

Wiring differences (old=new):
K=E, C=X.

L1108

106

Obsolete. Westinghouse; EM HEAT LED.

Y594R1243a

L1116

107

Obsolete. Carrier part no. HH93AZ171; SUPL HEAT
LED; used with T874D1264 (HH07AT173).

See OEM for
replacement.

L1132

108

Heil Quaker part no. HQ711598; used with T874R1137,
R1673, R1731, R1749, R1814; used in Y594R1110,
R1466, R1524, R1532, R1607.

Y594R1292a

L1140

109

Obsolete. Includes EM HEAT and AUX HEAT LEDs;
used with T874R1053; used in Y594G1136.

Y594R1763a

L1157

115

Obsolete. Rheem part no. 41-20796-14; EM HEAT and
AUX HEAT LEDs; used with T874R.

Q674L1207a

121

Obsolete. Used with T874C.

Y594C1322a

123

Obsolete. Used with T874R.

Y594R1243a

L1165

110

Obsolete. Lennox no. 24F5901; factory installed V-VR
jumper; EM HEAT and SERVICE LEDs; stage 2 heat is
isolated; used with T874C1448, R1178 and
C815A1013.

Y594R1763a

L1173

112

Obsolete. Westinghouse; AUX HEAT and EM HEAT
LEDs.

Y594R1243a

Both the thermostat and subbase must be replaced.

60-2485—8

82

Designed for use on Trane
heat pumps.

Wiring differences (old=new):
V-VR=R, M=Y, F=G, X=B,
Y=W, A=T, R=O, E=X2.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.

a

Model
Number

Fig.
No.

Q674 Trade
Replacement

L1181

113

Used with T874R1129; used in Y594R.

L1199

114

T8611M2025 Wiring differences (old=new):
Obsolete. Lennox no. 24F6001; used with T874D1207
and C815A1013.
(programmable) V-VR=R, Y=W3, X=C, R=O,
M=Y, M2=Y2-W2, F=G;
jumper Y2-W2; no outdoor
reset needed; use only one
system transformer.

L1207

115

Used with T874R1152, R1590, R1640, R1921; used in
Y594R1243, R1706.

Q674L1207 or
Y594R1243a

L1215

116

Obsolete. Crispaire heat pump; used with T874R1111;
used in Y594R1128.

Y594R1243a

L1223

117

Obsolete. Westinghouse special.

See OEM for
replacement.

L1231

182

Obsolete. Used with T874R1186 and W89.

None

L1249

115

Obsolete. Used with T874R1194 and W89.

Y594R1243a

L1256

118

Obsolete. Westinghouse special; used with
T874W1007.

T8611M2025 Includes night setback.
(programmable)

L1264

119

Obsolete. Intertherm heat pump; EM HEAT and SERV
LEDs; used with T874R1202, R1608, R1699; used in
Y594R1185, R1409, R1482.

Y594R1672a or Wiring differences (old=new):
Y594R1763a W2=W, X=B, Z=no
connection, K=X, W1=H.

L1272

120

Obsolete. York part no. 025-22290; used with
T874R1046, R1145; used in Y594R1011, R1102; used
with T874R1228, R1251 R1327 and C815A1039; used
in Y594R1144, R1151, R1193.

Y594R1672a

L1280

233

Obsolete. Lennox no. 52C7601; used with T874W1023
and W89.

Y594W1014a

L1298

182

Obsolete. Singer heat pump; used with T874R1160
and W89.

See OEM for
replacement.

L1314

115

Obsolete. Westinghouse heat pump; used with
T874R1244 and W89.

L1322

127

Obsolete. EM HEAT and AUX HEAT LEDs; used with
T874C1455.

Y594R1243a

L1330

120

Obsolete. York heat pump; used with T874R.

Y594R1664a

L1348

115

Obsolete. Williamson heat pump; used with
T874R1236.

Q674L1207

L1355

111,
190

Obsolete. Lennox part no. 31F3201; V-VR jumper;
used with T874C1448, R1178 and C815A1015.

Y594R1763a

Wiring differences (old=new):
V-VR=R, M=Y, F=G, X=B,
Y=W, A=T, R=O, E=X2.

L1363

129

Obsolete. York heat pump; EM HEAT LED; used with
T874G1402.

Y594R1425a

Wiring differences (old=new):
W=W2, X=E, B=X; jumper YW1.

L1371

124

Obsolete. BDP heat pump; part no. 34427DP125,
P272-1878; EM HEAT LED; used with T874J1010.

Y594J1001

Wiring differences (old=new):
W1=W2, F=L.

L1389

114

Obsolete. Lennox part no. 41F6501; V-VR jumper;
used with T874D1207.

Description

Y594R1243

a

Remarks
Wiring differences (old=new):
X1=X.

Replacement has auto fan in
emergency heat mode. Wiring
differences (old=new): A=L;
set anticipator to 1.2.

Q674L1207 or
Y594R1243a

Wiring differences (old=new):
L=X, X=B.

T8611M2025 Wiring differences (old=new):
(programmable) V-VR=R, Y=W3, X=C, R=O,
M=Y, M2=Y2-W2, F=G;
jumper Y2-W2; no outdoor
reset needed; use only one
system transformer.

Both the thermostat and subbase must be replaced.

83

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.

a

Model
Number

Fig.
No.

Q674 Trade
Replacement

L1397

103

Obsolete. Carrier part no. HH93AZ185A; SUPL HEAT
LED.

Y594G1393

L1405

106

Obsolete. BDP heat pump; part no. HH641501; used
with T874R1335; used in Y594R1201.

Y594R1243a

L1413

133

Obsolete. Fedders heat pump; used with T874R1343;
used in Y594R1219.

Y594R1425a

L1421

125

Obsolete. Coleman heat pump; used with T874R1368;
used in Y594R1235.

Y594R1797a

L1439

131

Obsolete. Carrier part no. HH93AZ187; SUPL HEAT
LED; System: SUPL HT-HEAT- COOL; used with
T874R1384 (HH07AQ170).

Q674L1207 or
Y594G1393a

Wiring differences (old=new):
C=X.

L1447

128

Obsolete. Williamson heat pump; three LEDs; used
with T874R1392; used in Y594R1250.

Y594R1425a

Wiring differences (old=new):
A=L.

L1454

131

Obsolete. Carrier part no. HH93AZ197; SUPL HEAT
LED; used with T874R1384 (HH07AQ170).

Y594R1393a

Wiring differences (old=new):
C=X.

L1462

113

Obsolete. LSI heat pump; part no. 104710002; used
with T874R1400.

Y594R1243a

Wiring differences (old=new):
X1=X.

L1496

136

Obsolete. Trane heat pump; used with T874R1426;
used in Y594R1284.

Y594R1763a

L1504

134

Rheem part no. 41-20796-24; used with T874R1442,
R1434, R1459; used in Y594R1631, R1649, R1854.

Y594R1300a

L1512

108

Includes two LEDs; used with T874R1467; used in
Y594R1292.

Y594R1292a

L1520

123

Includes EM HEAT and AUX HEAT LEDs; used with
T874R1475; used in Y594R1300.

Y594R1300a

L1538

130

Obsolete. Snyder General heat pump; used with
T874R1483, R1517, R1566 and C815A1005; used in
Y594R1318, R1342, R1375.

Y594R1763a

Wiring differences (old=new):
C=B, W1=W, E=X2, X=F.

132

Obsolete. Used with T874R1574, R1582; used in
Y594R1383, R1391.

Y594R1243a

Wiring differences (old=new):
C=X, X=L, W=W2.

L1546

140

Obsolete. Rheem part no. 41-20797-21; three LEDs;
used with T874W1031 and C815A1005; used in
Y594W1022.

L1553

137

Obsolete. Includes three LEDs; used with T874R1491;
used in Y594R1326.

Y594R1615a

L1561

121

Obsolete. Used with T874C1638; used in Y594C1322.

Y594C1322a

Use Y594C1322 when T874C
is used.

123

Obsolete. Used with T874R.

Y594R1243a

Use Y594R1243 when T874R
is used.

L1579

135

Obsolete. Carrier heat pump; part no. HH93AZ198;
SUPL HEAT LED; used with T874R1384
(HH07AQ170).

Y594R1243a

Wiring differences (old=new):
C=X.

L1587

168

Used with T874R1616; used in Y594R1425.

Y594R1425a

L1595

200,
201

Obsolete. Miller heat pump; used with T874R1624 or
T874R1202; used in Y594R1433.

L1603

134

Obsolete. Used with T874R1632.

Y594R1243a

L1611

136

Obsolete. American Standard heat pump; part no.
WY28X235; used with T874R1657; used in
Y594R1441.

Y594R1763a

Description

Both the thermostat and subbase must be replaced.

60-2485—8

84

a

Remarks
Wiring differences (old=new):
C=X.

Wiring differences (old=new):
K=E, C=X, Z=L; remove
W1-Y jumper.

T8611M2025 Includes night setback.
(programmable)

Y594R1243a or
Y594R1763a

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.

a

Model
Number

Fig.
No.

Q674 Trade
Replacement

L1637

207

Obsolete. Carrier heat pump; part no. HH93AZ195;
used with T874J1002 (HH07AT175) or T874J1010
(HH07AT165).

L1678

209

Trol-A-Temp by Honeywell; gray color; used with
T874R1707; used in Y594R1490.

None

See Trol-A-Temp.

L1686

209

Trol-A-Temp by Honeywell; used with T874R1715;
used in Y594R1508.

None

See Trol-A-Temp.

L1702

132

Obsolete. Snyder General heat pump; part no.
654958B07; used with T874R1723 and C815A1005;
used in Y594R1516.

Y594R1672a

L1710

230

Used with T874R1822; used in Y594R1615.

Y594R1615a

L1728

228

Obsolete. Lennox; gray color; used with T874R1855;
used in Y594R1714.

Y594R1763a

L1736

120

Designed to replace Y594R1011 (York part no.
2TH11702224); used with T874R1871; used in
Y594R1664.

Y594R1664a

Designed to replace Y594R1151 (York part no.
2TH11702324), Y594R1193 (York part no.
6TH11702224) and York part no. 2TH11704024; used
with T874R1889 and C815A1054; used in Y594R1672.

Y594R1672a

Description

Remarks

a

Y594J1001

Wiring differences (old=new):
C=B, W1=W, X=X2.

Wiring differences (old=new):
Y1=Y, L=F, W1=W, E=X2, C=B.

L1751

230

Gray color; used with T874R1897, used in
Y594R1680.

Y594R1680a

L1769

124

Obsolete. Nordyne part no. 9132260; used with T874J.

See OEM for
replacement.

L1777

120

Obsolete. Gray color; designed to replace Y594R1151
(York part no. 2TH11702324), Y594R1193 (York part
no. 6TH11702224) and York part no. 2TH11704024;
used with T874R1905 and C815A1059; used in
Y594R1698.

Y594R1672a

Replacement is beige.

Designed to replace Y594R1011 (York part no.
2TH11702224); used with T874R1913; used in
Y594R1706.

Y594R1664a

Replacement is beige.

Wiring differences (old=new):
C=X; Y1-W1 jumper required.

L1785

103

Obsolete. Carrier part no. HH93AZ175-W; Canada;
gray color; System: Supl Ht-Heat-Off-Cool; includes
one LED.

Y594G1476a

L1793

124

Obsolete. Carrier Canada part no. HH93AZ186-W;
gray color; Fan: Auto-On; System: Supl Ht-Heat-OffCool; includes one LED.

Y594J1019a

L1801

197

American Standard (Trane) part no. THT1225; includes
two LEDs; used with T874R1939; used in Y594R1748.

Y594R1763a

L1819

168

Obsolete. Inter-City Products part no. HQ1149407HW;
includes three LEDs; used with T874R1947; used in
Y594R1755.

Y594R1425a

L1827

197

TRADELINE; includes two LEDs; used with
T874R1954; used in Y594R1763; direct replacement
for Trane/American Standard Y594R1748
(T874R1939/Q674L1801) Trane part no. ASYSTAT
631A, Y594R1136 (T874R1053/Q674L1140).

Y594R1763a

L1835

140

Obsolete. Inter-City Products; includes three LEDs;
used in Y594W1030.

L1843

115

Obsolete. Consolidated Industries part no. 9036100;
gray color; includes two LEDs; used with T874R1962;
used in Y594R1771.

T8611M2025a Includes night setback.
(programmable)
Y594R1680a

Includes CHECK LED.

Both the thermostat and subbase must be replaced.

85

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 9. Q674 Subbase Cross Reference.
Model
Number

Fig.
No.

L1850

120

York Canada; gray color; includes one LED; used with
T874R1970; used in Y594R1789.

Y594R1672

L1868

125

TRADELINE; includes two LEDs; used with
T874R1988; used in Y594R1797; direct replacement
for Evcon/Coleman Y594R1235 (T874R1368/
Q674L1421) Coleman part no. 3600-368.

Y594R1797a

L1876

245

Obsolete. Amana part no. 10573902; includes two
LEDs; used with T874R2002; used in Y594R1805.

Y594R1797

Wiring differences (old=new):
C/X=X.

L1884

245

Obsolete. Amana part no. 10573904; includes two
LEDs; used with T874R2010; used in Y594R1813.

Y594R1797

Wiring differences (old=new):
C/X=X, W3=W2.

L1892

103

Obsolete. TRADELINE; System: SUPL HT-HEATOFF-COOL; includes one LED; used with T874G2004;
used in Y594G1666; direct replacement for Carrier
Y507J1011 (T874G1055/Q674L1041) Carrier part no.
HH07AT171/HH93AZ175.

Y594G1674

Replacement has auto
changeover.

L1900

241

Obsolete. TRADELINE; System: SUPL HT-HEATOFF-COOL; includes SUPL HT LED; used with
T874J1069; used in Y594J1001; direct replacement for
Carrier T874J1028/Q674J1068 (Carrier part no.
HH07AT165/HH93AZ183), Carrier T874J1002/
Q674J1068 (Carrier part no. HH07AT175/
HH93AZ183).

Y594J1019

Replacement has auto
changeover.

L1918

125

Obsolete. York logo; part no. 2TH11703424A; includes
two LEDs; used with T874R2028 in Y594R1821.

Y594R1797a

L1934

123

Obsolete. Addison logo; part no. 843-277; includes
three LEDs; used with T874W1106 in Y594W1055.

T8611M2025

N1015

60

Obsolete. Goettl heat pump; changeover in heat mode;
evaporative cooler circuit; used with T874C1182.

See OEM for
replacement.

N1023

61

Obsolete. Sigler heat pump; evaporative cooler circuit;
used with T874C1349.

See OEM for
replacement.

Q674N

System: SUPL HT-HEAT-COOL; Fan: AUTO-ON
126

Q674Q
59

Obsolete. McQuay special; used with T874A1267.

Q1012

64

Used with T874A1291.

69

None

Obsolete. Carrier part no. HH93AZ190; international
symbols on fan and switches; used with T874V1008
(HH07AT177).

70

Obsolete. Fiberglas; Canada; SERVICE LED; used
with T874C1653; used in Y594C1348.

See OEM for
replacement.

System: OFF-ON; Fan: LO-MED-HI
240

Obsolete. Snyder General part no. 044271801.

Both the thermostat and subbase must be replaced.

60-2485—8

See OEM for
replacement.

System: HEAT-COOL; Fan: None

Q674W
W1006

See OEM for
replacement.

System: OFF-COOL; Fan: LO-HI-CONT

Q674S
S1000

Y594G1419a

System: HEAT-OFF-COOL; Fan: LOW-MED-HI-ON

Q674R

a

Obsolete. Carrier heat pump; part no. HH93AZ169;
used with T874G1071 (HH07AT171).

Q1004

R1003

Remarks

a

System: OFF-HEAT-COOL-EVAP; Fan: AUTO-ON

Q674P
P1005

Q674 Trade
Replacement

Description

86

See OEM for
replacement.

Wiring differences (old=new):
C=X; jumper Y1-W1;
replacement has OFF-EM HTHEAT-AUTO-COOL system
switching.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacementa

Description

Remarks

Y594A
A1001

46

Obsolete. Amana part no. D68535-11; contains
T874A1077, Q674B1075.

T874A1036/
Q674B1075

A1019

82

Obsolete. Amana part no. P68535-12; contains
T874A1077, Q674E1056.

T874A1036/
Q674E1049

A1035

44

Obsolete. Trane part no. 268-0187-1; contains
T874A1085, Q674B1018.

T874A1036/
Q674B1018

A1043

46

Obsolete. Trane part no. 268-0201-5; contains
T874A1085, Q674B1075.

T874A1036/
Q674B1075

55, 66 Obsolete. Trane part no. 268-0201-3; contains
T874A1085, Q674D1008.

T874A1036/
Q674D1040

A1050
A1068

82

Obsolete. Sears part no. 42-9144; contains
T874A1119, Q674E1007.

T874A1036/
Q674E1049

A1126

64

Contains T874A1291, Q674Q1012.

A1159

91

Obsolete. Contains T874A1440, Q674G1005.

T874A1150/
Q674G1070

None

A1167

184

California Economizer; Premier White® color;
contains T874A1580 and Q674G1161.

T874A1036/
Q674G1070

A1175

55

Obsolete. York logo; part no. 2TH04703224;
contains T874A1622, Q674D1180.

T874A1010/
Q674D1040

A1191

46

Obsolete. Amana logo: part no. P6853524R;
contains T874A1002, Q674B1075.

T874A1036/
Q674B1075

B1026

44

Trane part no. BAYSTAT012; contains T874B1035,
Q674B1018.

T874B1019/
Q674B1018

B1034

46

Obsolete. Trane part no. 163-552-1; contains
T874B1035, Q674B1075.

T874B1019/
Q674B1075

B1042

88

Obsolete. Goodman part no. CHTS36-60; contains
T874B1100, Q674E1338.

T874B1019/
Q674E1049

No LEDs on replacement.

C1009

82

Obsolete. Amana part no. D68535-9; contains
T874C1059, Q674E1056.

T874C1018/
Q674E1049

Jumper RC-RH.

C1017

142

Obsolete. Amana part no. D68535-10; contains
T874C1059, Q674F1022.

T874C1018/
Q674F1022

C1058

46

Obsolete. Contains T874C1000, Q674B1075.

T874C1018/
Q674B1075

C1082

82

Obsolete. Trane part no. 166-162-1; contains
T874C1083, Q674E1007.

T874C1018/
Q674E1049

C1256

45

Obsolete. Amana part no. D68535-16; contains
T874C1059, Q674B1059.

T874C1018/
Q674B1034

C1280

45

Obsolete. Williamson; contains T874C1570,
Q674B1000.

T874C1018/
Q674B1034

C1314

56

Obsolete. LSI; contains T874C1471, Q674B1257.

T874C1018/
Q674B1018

C1322

121

Obsolete. Contains T874C1638, Q674L1561.

Y594C1322

C1330

142

Obsolete. Amana part no. D68535-21; contains
T874C1059, Q674F1022.

T874C1018/
Q674F1022

Replacement is beige color.

Y594B

Y594C

a

Jumper RC-RH.

Jumper RC-RH; no RESET
LED on replacement.

Both the thermostat and subbase must be replaced.

87

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacementa

Description

Remarks

C1348

70

Obsolete. Fiberglas; contains T874C1653,
Q674S1000.

T874C1000/
Q674B1075

C1355

45

Obsolete. Nordyne “Miller” part no. 9122250;
contains T874C1695, Q674B1000.

T874C1018/
Q674B1034

C1363

45

Obsolete. Nordyne “Intertherm” part no. 911100001;
contains T874C1703, Q674B1000.

T874C1018/
Q674B1075

C1371

184

Obsolete. California Economizer; contains
T874C1802 and Q674G1005.

T874C1018/
Q674G1070

C1389

237

Obsolete. TRADELINE; Premier White® color;
contains T874C1810 and Q674B1547.

Y594C1389

C1413

238

Heat Controller “Energy Night” logo; contains
T874C1844 and Q674F1592.

Y594R1425

E-W2 jumper required; system:
EM.HT.-Heat-Off-Cool.

C1421

249

Obsolete. TRADELINE; contains T874C1877 and
Q674B1554.

Y594D1347

Replacement has auto
changeover; jumper RH-RC.

C1439

T874C1869 and Q674C1579.

Wiring differences (old=new):
Y=Y1; jumper RC-RH and Y1W1; replacement has no
SERVICE LED; replacement
has fan switching and HEATOFF-COOL system switching.

Wiring differences (old=new):
Y=Y1; jumper RC-RH; Y1-W;
replacement has no SERVICE
LED.

None

Y594D
D1016

44

Obsolete. Trane part no. 268-0201-2; contains
T874D1082, Q674B1018.

T874D1165/
Q674B1018

D1024

72

Trane part no. BAYSTAT010; contains T874D1082,
Q674C1009.

T874D1165/
Q674C1058

D1032

91

Obsolete. Trane part no. BAYSTAT011; contains
T874D1082, Q674G1021.

T874D1165/
Q674G1070

D1040

46

Amana part no. P68535-19R; contains T874D1082,
Q674B1075.

T874D1165/
Q674B1075

D1057

a

55, 66 Obsolete. Trane part no. BAYSTAT007; contains
T874D1082, Q674D1008.

T874D1165/
Q674D1040

D1149

46

Obsolete. Amana part no. P68535-20C; contains
T874D1322, Q674B1075.

T874D1165/
Q674B1075

D1156

48

Obsolete. Trane part no. BAYSTAT013; contains
T874D1082, Q674B1133.

T874D1165/
Q674B1018

D1180

82

York part no. 025-23321-000; contains T874D1504,
Q674E1007.

T874D1165/
Q674E1049

D1222

166

Obsolete. WeatherKing; contains T874D1009,
Q674F1337.

T874D1165/
Q674F1022

D1248

82

Obsolete. Reznor part no. 93437; contains
T874D1629, Q674E1007.

T874D1165/
Q674E1049

D1297

82

Obsolete. ArcoAire part no. 1506753; contains
T874D1769, Q674E1346.

T874D1165/
Q674E1049

D1305

82

Obsolete. Comfortmaker part no. 1505753; contains
T874D1785, Q674E1346.

T874D1165/
Q674E1049

D1321

45

Obsolete. Goodman part no. CHT 90-120; contains
T874D1843, Q674B1000.

T874D1165/
Q674B1034

D1339

82

Obsolete. Nordyne part no. 5471180; contains
T874D1009, Q674E1007.

T874D1165/
Q674E1049

Both the thermostat and subbase must be replaced.

60-2485—8

88

Replacement has no FILTER
LED.

Wiring differences (old=new):
R=RH; jumper RC-RH;
replacement has no EM.HT. or
AUX. HT. LEDs.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.
Model
Number

Fig.
No.

Trade Model
Replacementa

Description

Remarks

D1347

82

TRADELINE® contains T874D1942, Q674E1403.

Y594D1347

D1354

82

SUPER TRADELINE® contains T874D2031 (no
cover), Q674E1049, and TG504A with two keys.

Y594D1354

D1370

45

Obsolete. Carrier part no. 50QE90022101; contains
T874D2049 and Q674B1539.

T874D1165/
Q674B1034

Replacement has °F
scaleplate.

D1388

72

Obsolete. Carrier part no. 50QE90023101; contains
T874D2049 and Q674C1520.

T874D1165/
Q674C1058

Replacement has °F
scaleplate.

D1396

184

Obsolete. Carrier part no. 50QE90025101; contains
T874D2049 and Q674G1153.

T874D1165/
Q674G1070

Replacement has °F
scaleplate.

55, 66 Obsolete. Carrier part no. 50QE90024101; contains
T874D2049 and Q674D1164.

T874D1165/
Q674D1040

Replacement has °F
scaleplate.

D1404
D1412

82

Obsolete. Carrier “Weathermaker” part no.
HH07AT209; taupe color; contains T874D2064 and
Q674E1445.

T874D1165/
Q674E1049

Replacement is beige color.

D1420

82

Obsolete. Carrier “Zone Perfect” part no.
HH07AT208; taupe color; contains T874D2072 and
Q674E1445.

T874D1165/
Q674E1049

Replacement is beige color.

D1438

55, 66 Obsolete. Contains T874D2098 and Q674D1008.

T874D1165/
Q674D1040

Replacement has 2 setpoint
levers.

D1446

55, 66 Obsolete. Contains T874D2106 and Q674D1008.

T874D1165/
Q674D1040

Replacement has °F
scaleplate and 2 setpoint
levers.

D1453

208

Obsolete. Amana logo; part no. P1217501F;
contains T874D2163 and Q674D1172.

T874D1165/
Q674D1040

D1461

45

Obsolete. Amana logo; part no. P1217701F;
contains T874D2171 and Q674B1562.

T874D1942/
Q674B1034

72

Obsolete. Trane part no. BAYSTAT015; contains
T874E1040, Q674C1009.

T874B1019/
Q674C1058

F1022

44

Obsolete. Contains T874F1031 and 40003440-001
wallplate with installed diode.

T874F1015

F1048

72

Obsolete. Reznor part no. 93436; contains
T874F1130, Q674C1009.

T874F1015/
Q674C1058

F1063

91

Obsolete. Reznor part no. 93435; contains
T874F1130, Q674G1005.

T874F1015/
Q674G1070

G1013

160

Obsolete. York part no. 2TH11702424; contains
T874G1170, Q674J1027.

Y594G1567

G1138

160

Obsolete. York part no. 025-22286; contains
T874G1196, Q674J1027.

Y594G1567

G1153

154

Obsolete. Crispaire part no. HP10-51; contains
T874G1089, Q674F1204.

Y594G1252

G1161

162

Contains T874G1204, Q674J1043.

Y594G1161

G1195

155

Obsolete. Heil Quaker part no. HQ521387HW;
contains T874G1246, Q674F1212.

Y594G1252

G1229

160

Obsolete. York part no. 6TH11702424; contains
T874G1428, Q674J1027.

Y594G1567

G1245

155

Obsolete. BDP part no. HH641502; contains
T874G1451, Q674F1212.

Y594G1252

G1252

155

TRADELINE; contains T874G1246, Q674F1212.

Y594G1252

Y594E
E1015
Y594F

Y594G

a

Wiring differences (old=new):
A=L.

Both the thermostat and subbase must be replaced.

89

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.

a

Trade Model
Replacementa

Model
Number

Fig.
No.

G1294

79

Obsolete. LSI; contains T874G1378, Q674C1124.

See OEM for
replacement.

H2 is night setback.

G1328

194

Obsolete. Addison part no. 8403-197; contains
T874G1543, Q674F1345.

Y594G1252

Wiring differences (old=new):
Y1=O, X=L, C=X.

G1344

194

Obsolete. Heat Controller part no. 7601-110B;
contains T874G1469, Q674F1345.

Y594G1252

Wiring differences (old=new):
Y1=O, X=L, C=X; W1=Y.

G1351

160

Obsolete. Luxaire part no. 026-00068-000; contains
T874G1568, Q674J1126.

Y594G1567

G1369

155

Obsolete. Contains T874G1246, Q674F1212.

Y594G1252

G1377

169

Obsolete. Coleman part no. 3600-373; contains
T874G1576, Q674F1402.

Y594G1633

G1385

155

Obsolete. ArcoAire; contains T874G1592,
Q674F1212.

Y594G1252

G1393

170

Obsolete. Contains T874R1393, Q674L1454.

Y594G1393

G1419

227

TRADELINE; contains T874G1642, Q674F1444.

Y594G1419

G1427

177

Obsolete. Mammoth part no. 73034101; contains
T874G1659, Q674C1330.

See OEM for
replacement.

G1443

174

Obsolete. American Standard (Trane) part no.
ASYSTAT650; contains T874G1675, Q674J1142.

Y594G1161

G1476

227

TRADELINE; same as Y594G1419 except Premier
White® color; contains T874G1741, Q674F1477.

Y594G1476

G1492

211

Trol-A-Temp; contains T874G1758, Q674F1485.

G1500

216

Obsolete. Comfortmaker part no. 1505756; contains
T874G1774, Q674J1175.

See OEM for
replacement.

G1518

216

Obsolete. ArcoAire part no. 1506756; contains
T874G1782, Q674J1175.

See OEM for
replacement.

G1526

167

TRADELINE; contains T874G1626, Q674F1436.

None

G1534

227

TRADELINE; °C; white; Australia; contains
T874G1824, Q674F1477.

None

G1542

231

Obsolete. Intertherm part no. 9129290; contains
T874G1832, Q674F1519.

Y594G1252

Cooling changeover only.

G1559

231

Obsolete. Miller part no. 9129310; contains
T874G1840, Q674F1519.

Y594G1252

Cooling changeover only.

G1567

160

TRADELINE; contains T874G1865, Q674J1209.

Y594G1567

G1575

160

Obsolete. TRADELINE; same as Y594G1567
except Premier White® color; contains T874G1873,
Q674J1225; direct replacement for York
2TH11702424 (Y594G1013 contains T874G1170/
Q674J1027) and 6TH11702424 (Y594G1229
contains T874G1428/Q674J1027).

Y594G1567

Replacement is beige.

G1583

229

Obsolete. Lennox Canada part no. 97E78; contains
T874G1857, Q674F1535.

Y594G1161

Wiring differences (old=new):
E=X2, C=B, L=F.

G1591

243

Obsolete. Amana part no. 10636701; contains
T874G1899 and Q674F1550.

Y594G1633

G1609

155

Obsolete. Econar; contains T874G1915 and
Q674F1212.

Y594G1252

Description

Both the thermostat and subbase must be replaced.

60-2485—8

90

None

Remarks

H2 is night setback.

See Trol-A-Temp for
replacement.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.
Model
Number

Fig.
No.

G1617

73

Trade Model
Replacementa

Description
Obsolete. Carrier part no. 50QE90020101; contains
T874G1949 and Q674C1504.

Y594H1012

a

Remarks
Wiring differences (old=new):
Y1=O, Y2=Y, L=R, R=none;
R-L jumper required; no night
setback.

Wiring differences (old=new):
T8600D2028
(programmable) Y1=O, Y2=Y, L=R; W-Y jumper
required; night setback.
G1625

160

York Canada part no. 2TH11702524; contains
T874G1964 and Q674J1266.

Y594G1567a

Replacement has °F
scaleplate.

G1633

169

TRADELINE; contains T874G1972 and
Q674F1584; direct replacement for Y594G1377
(T874G1576/Q674F1402) Evcon/Coleman part no.
3600-373.

Y594G1633a

G1641

169

Obsolete. Amana part no. 10636703; contains
T874G1980 and Q674F1600.

Y594G1633

G1658

155

Obsolete. Tempstar “Inter-City Products” part no.
1149910; contains T874G1998 and Q674F1212.

Y594G1252

G1666

103

Obsolete. TRADELINE; manual changeover;
contains T874G2004 and Q674L1892; direct
replacement for Y507J1011 (T874G1055/
Q674L1041) Carrier part no. 99TZ90041106
(HH07AT171/HH93AZ1750).

Y594G1674

G1674

161

TRADELINE; automatic changeover; contains
T874G2004 and Q674J1274; direct replacement
Y507J1003 (T874G1055/Q674J1035) Carrier part
no. 99TZ90040106 (HH07AT171/HH93AZ173).

Y594G1674

G1716

155

WaterFurnace logo; part no. TA21H03; contains
T874G2046 and Q674F1667.

Y594G1716

H1004

79

Obsolete. LSI part no. 73033901; contains
T874H1039 and Q674C1124.

T8600D2028

H1012

164

Contains T874H1062 and Q674C1249; replaces
T874H1005/Q674C1041.

Y594H1012

H1020

177

Obsolete. Mammoth part no. 71117101; contains
T874H1096 and Q674C1330.

Y594H1012

Wiring differences (old=new):
R1=R, R2=L; use jumper
provided.

H1038

74

Obsolete. Carrier part no. 50QE90019101; contains
T874H1161 and Q674C1496.

Y594H1012a

Wiring differences (old=new):
X1=O, Y2=Y; L-R jumper
required.

H1046

172

Obsolete. Carrier part no. 50QE90026101; contains
T874H1153 and Q674B1406.

T874A1130/
Q674B1075a

Wiring differences (old=new):
Y=Y1; W1-Y1 jumper required;
replacement has no LEDs.

H1053

173

Obsolete. Carrier part no. 50QE90027101; contains
T874H1153 and Q674C1322.

Y594H1012a

Wiring differences (old=new):
Z=X.

241

Obsolete. TRADELINE; manual changeover;
contains T874J1069 and Q674L1900; direct
replacement for T874J1002 or T874A1028 used
with Q674L1074 or Q674L1637 (HH07AT175 or
HH07AT165 used with HH93AZ186 or
HH93AZ195).

(Recontrol)
T8511G1021

Wiring differences (old=new):
W3=W2.

Replacement has auto
changeover.

Y594H
H2 is night setback.

Y594J
J1001

a

Both the thermostat and subbase must be replaced.

91

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.
Trade Model
Replacementa

Model
Number

Fig.
No.

J1019

244

Obsolete. TRADELINE; automatic changeover;
contains T874J1069 and Q674J1282; direct
replacement for T874J1002 or T874J1028 used
with Q674J1068 or Q674J1159 (HH07AT175 or
HH07AT165 used with HH93AZ183 or
HH93AZ196).

(Recontrol)
T8511G1021

N1007

178

Obsolete. Williamson part no. 75-189; contains
T874N1008 and Q674F1196.

T874N1016/
Q674F1196

N1015

179

Obsolete. Contains T874N1040 and Q674F1261.

Y594G1419a

N1023

178

Obsolete. Intertherm part no. 9111882; contains
T874N1057 and Q674F1220.

T874N1016/
Q674F1220

N1031

178

Obsolete. Nordyne “Miller” part no. 9122240;
contains T874N1065 and Q674F1220.

T874N1016/
Q674F1220

97

Obsolete. Carrier part no. 50QE90021101; contains
T874P1055 and Q674C1512.

T8600D2028

R1011

120

Obsolete. York part no. 2TH11702224; contains
T874R1046 and Q674L1272.

Y594R1664

R1029

47

Obsolete. Bryant; contains T874R1004 and
Q674B1042.

Y594R1243

Wiring differences (old=new):
W1=W2.

R1037

122

Obsolete. Fedders part no. 88-58-00540-001;
contains T874R1269 and Q674L1066.

Y594R1615

Wiring differences (old=new):
K=E, C=X, W1=B, Z=L.

R1102

120

Obsolete. York part no. 025-22285-000; contains
T874R1145 and Q674L1272.

Y594R1664

R1110

108

Obsolete. Heil Quaker part no. HQ712004HW;
contains T874R1137 and Q674L1132.

Y594R1292

R1128

116

Obsolete. Crispaire part no. HP9-51; contains
T874R1111 and Q674L1215.

Y594R1243

R1136

109

Obsolete. Contains T874R1053 and Q674L1140.

Y594R1763

R1151

120

Obsolete. York part no. 2TH11702324; contains
T874R1251, Q674L1272 and C815A1039.

Y594R1672

R1185

201

Obsolete. Intertherm part no. 9111871; contains
T874R1202 and Q674L1264.

Y594R1672

R1193

120

Obsolete. York part no. 6TH11702224; contains
T874R1327 and Q674L1272.

Y594R1664

R1201

106

Obsolete. BDP part no. HH641501; contains
T874R1335 and Q674L1405.

Y594R1243

R1219

133

Obsolete. Fedders part no. 88-58-00560-001;
contains T874R1343 and Q674L1413.

Y594R1425

R1235

125

Obsolete. Coleman part no. 3600-368; contains
T874R1368 and Q674L1421.

Y594R1797

R1243

115

TRADELINE; contains T874R1152 and Q674L1207.

Y594R1243

R1250

128

Obsolete. Williamson part no. 75-191; contains
T874R1392 and Q674L1447.

Y594R1425

R1284

136

Obsolete. Trane part no. BAYSTAT339; contains
T874R1426 and Q674L1496.

Y594R1763

Description

Remarks

Y594N

Wiring differences (old=new):
L=X2, Y=Y1.

Y594P
P1005

Wiring differences (old=new):
Y=Y1, W=O; Y1-W1 jumper
required.

Y594R

a

Both the thermostat and subbase must be replaced.

60-2485—8

92

Wiring differences (old=new):
A=L.

Wiring differences (old=new):
W2=W, X=B, Z=no
connection, K=X, W1=H.

Wiring differences (old=new):
K=E, C=X, Z=L; remove
factory installed jumper.

Wiring differences (old=new):
A=L.

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.

a

Trade Model
Replacementa

Model
Number

Fig.
No.

R1292

108

Contains T874R1467 and Q674L1512; replaces
Y594R1110 (T874R1137/Q674L1132).

Y594R1292

R1300

123

Contains T874R1475 and Q674L1520.

Y594R1300

R1318

130

Obsolete. Comfortmaker part no. 1505721; contains
T874R1483, Q674L1538 and C815A1005.

Y594R1763

R1326

137

Obsolete. SUPER TRADELINE; contains
T874R1491 and Q674L1553.

Y594R1615

R1334

47

Obsolete. Slant Fin; contains T874R1509 and
Q674B1042.

Y594R1243

Wiring differences (old=new):
W1=W2.

R1342

130

Obsolete. ArcoAire part no. 1506721; contains
T874R1517, Q674L1538 and C815A1005.

Y594R1763

Wiring differences (old=new):
W1=W, E=X2, X=F, C=B.

R1359

113

Obsolete. ArcoAire part no. A02074; contains
T874R1525 and Q674L1181.

Y594R1243

Wiring differences (old=new):
X1=X.

R1375

130

Obsolete. Contains T874R1566, Q674L1538 and
C815A1005.

Y594R1763

Wiring differences (old=new):
W1=W, E=X2, X=F, C=B.

R1383

132

Obsolete. Comfortmaker part no. 1505739; contains
T874R1574 and Q674L1538.

Y594R1243

Wiring differences (old=new):
W=W2, C=X, X=L.

R1391

132

Obsolete. ArcoAire part no. 1506739; contains
T874R1582 and Q674L1538.

Y594R1243

Wiring differences (old=new):
W=W2, C=X, X=L.

R1409

119

Obsolete. Intertherm part no. 6244630; contains
T874R1608 and Q674L1264.

Y594R1763

Wiring differences (old=new):
W2=W, X=B, Z=F, K=X2,
W1=O.

R1417

113

Obsolete. Comfortmaker part no. 1505-735;
contains T874R1301 and Q674L1181.

Y594R1243

Wiring differences (old=new):
X1=X.

R1425

168

SUPER TRADELINE; contains T874R1616 and
Q674L1587.

Y594R1425

R1433

200

Obsolete. Miller part no. 9115900; contains
T874R1624 and Q674L1595.

Y594R1243

R1441

136

Obsolete. American Standard (Trane) part no.
ASYSTAT651; contains T874R1657 and
Q674L1611.

Y594R1763

R1466

108

Heil Quaker part no. 1060321; model no.
HAXB004TW01; contains T874R1673 and
Q674L1132.

Y594R1292

R1482

119

Obsolete. Nordyne “Miller” part no. 9122230;
contains T874R1699 and Q674L1264.

Y594R1763

R1490

209

Trol-A-Temp; contains T874R1707 and Q674L1678.

None

See Trol-A-Temp for
replacement.

R1508

209

Trol-A-Temp; contains T874R1715 and Q674L1686.

None

See Trol-A-Temp for
replacement.

R1516

132

Obsolete. Snyder General part no. 654958B07;
contains T874R1723, Q674L1702 and C815A1005.

Y594R1763

R1524

108

Obsolete. Inter-City Products part no.
HQ1147925HW; contains T874R1731 and
Q674L1132.

Y594R1292

R1532

108

Heil Quaker part no. 1060322; model no.
TAXB004TW01; contains T874R1749 and
Q674L1132.

Y594R1292

R1607

108

Obsolete. Keeprite THPC; contains T874R1814 and
Q674L1132.

Y594R1292

Description

Remarks

Wiring differences (old=new):
W1=W, E=X2, X=F, C=B.

Wiring differences (old=new):
W2=W, X=B, Z=F, K=X2,
W1=O.

Wiring differences (old=new):
W2=W, X=B, Z=F, K=X2,
W1=O.

Wiring differences (old=new):
W1=W, C=B, X=X2.

Both the thermostat and subbase must be replaced.

93

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.

a

Trade Model
Replacementa

Model
Number

Fig.
No.

R1615

230

TRADELINE; contains T874R1822 and
Q674L1710; replaces Y594R1326 (T874R1491/
Q674L1553).

Y594R1615

R1623

134

Obsolete. Rheem Universal Parts part no. 4120796-46; contains T874R1558 and Q674L1504.

Y594R1300

R1631

134

Rheem part no. 41-20796-29; contains T874R1442
and Q674L1504.

Y594R1300

R1649

134

Ruud part no. 41-20796-33; contains T874R1434
and Q674L1504.

Y594R1300

R1656

134

Obsolete. WeatherKing part no. 41-20796-64;
contains T874R1830 and Q674L1504.

Y594R1300

R1664

120

TRADELINE; contains T874R1871 and
Q674L1736; direct replacement for York
2TH11702224 (Y594R1011 contains T874R1046/
Q674L1272).

Y594R1664

R1672

120

TRADELINE; contains T874R1889, Q674L1736
and C815A1054; direct replacement for York
2TH11702324 (Y594R1151 contains T874R1251/
Q674L1272/C815A1039) and 6TH11702224
(Y594R1193 contains T874R1327/Q674L1272).

Y594R1672

R1680

230

TRADELINE; same as Y594R1615 except Premier
White® color; contains T874R1897 and
Q674L1751; direct replacement for Y594R1326
(T874R1491/Q674L1553).

Y594R1680

R1698

120

Obsolete. TRADELINE; Premier White® color;
contains T874R1905, Q674L1777 and C815A1054.

Y594R1672

Replacement is beige.

R1706

120

Obsolete. TRADELINE; same as Y594R1664
except Premier White® color; contains T874R1913
and Q674L1777; direct replacement for Y594R1011
(T874R1046/Q674L1272) York part no.
2TH11702224.

Y594R1664

Replacement is beige.

R1714

228

Obsolete. Lennox part no. 97E79; Canada; Premier
White® color; contains T874R1855 and
Q674L1728.

Y594R1763

Wiring differences (old=new):
Y1=Y, L=F, W1=W, E=W2,
C=B.

R1722

115

Obsolete. Econar; contains T874R1921 and
Q674L1207.

Y594R1243a

R1748

197

American Standard (Trane) part no. ASYSTAT651A;
contains T874R1939 and Q674L1801.

Y594R1763a

R1755

168

Obsolete. Inter-City Products part no.
HQ1149376HW; contains T874R1947 and
Q674L1819.

Y594R1425a

R1763

197

TRADELINE: contains T874R1954 and
Q674L1827; direct replacement for Y594R1136
(T874R1053/Q674L1140), Y594R1748
(T874R1939/Q674L1801) Trane part no.
ASYSTAT651A, Y594R1441 (T874R1657/
Q674L1611) Trane part no. ASYSTAT651.

Y594R1763

R1771

115

Obsolete. Consolidated Industries part no.
9036100; contains T874R1962 and Q674L1843.

Y594R1680a

Includes CHECK LED.

R1789

120

York Canada part no. 2TH11701524; contains
T874R1970 and Q674L1850.

Y594R1672a

Replacement has °F
scaleplate.

Description

Both the thermostat and subbase must be replaced.

60-2485—8

94

Remarks

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

Table 10. Y594 Cross Reference.
Trade Model
Replacementa

Model
Number

Fig.
No.

R1797

125

TRADELINE; contains T874R1988 and
Q674L1868; direct replacement for Y594R1235
(T874R1368/Q674L1421) Evcon/Coleman part no.
3600-368).

Y594R1797

R1805

245

Obsolete. Amana part no. 10636702; contains
T874R2002 and Q674L1876.

Y594R1797

Wiring differences (old=new):
C/X=X.

R1813

245

Obsolete. Amana part no. 10636704; contains
T874R2010 and Q674L1884.

Y594R1797

Wiring differences (old=new):
C/X=X, W3=W2.

R1821

125

Obsolete. York logo; part no. 2TH11703424A;
contains T874R2028 and Q674L1918.

Y594R1797

R1839

134

Rudd logo; part no. 41-20796-48; contains
T874R2036 and Q674L1504.

See OEM for
replacement.

R1854

123

Obsolete. Rheem logo; part no. 41-20796-47;
contains T874R1996 and Q674L1504.

Y594R1300

W1014

54

Contains T874W1015, Q674B1216 and
C815A1005.

Y594W1014

W1022

140

Obsolete. Rheem part no. 41-20797-19; contains
T874W1031, Q674L1546 and C815A1005.

T8611M2025.

W1030

68

Obsolete. Inter-City Products part no. 1072350;
contains T874W1072, Q674L1835 and C815A1005
Outdoor Thermistor.

W1055

247

Obsolete. Addison logo; part no. 843-277; contains
T874W1106, Q674L1934 and C815A1005.

T8611M2025

Y1004

210

Obsolete. Mammoth part no. 71117301; contains
T874Y1005 and Q674E1353.

See OEM for
replacement.

Y1012

248

Obsolete. WaterFurnace logo; part no. TA21H03;
contains T874Y1013 and Q674F1675.

Description

Remarks

a

Y594W

T8611M2025
Includes night setback.
(programmable)

Y594Y

a

Both the thermostat and subbase must be replaced.

95

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

WIRING DIAGRAMS
SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1

RH
HEAT RELAY 1
W1

1
FAN
SWITCH

H1
FALL

HEAT RELAY 2

AUTO

W2

H1 ANTICIPATOR
HEAT CHANGEOVER
VALVE

ON

H2

2
6
H2 ANTICIPATOR

FALL

SYSTEM
SWITCH

COOL CHANGEOVER
VALVE

O

8

FAN RELAY
HEAT

G

C1

RISE

NOTE:
Model
ing
No.
T874A
T874B
T874C
T874D
T874E
T874D

B

4

OFF
9

Heating CoolBulbs
H1
H1
H1,H2
H1,H2

Bulbs
C1
C1,C2
C1
C1,C2
C1,C2

H1,H2

COMPRESSOR
CONTACTOR 2

COOL
Y2

COMPRESSOR
CONTACTOR 1

10
C1 ANTICIPATOR
Y1
C2 ANTICIPATOR

L2

11

RISE

L1
(HOT)

RC

C2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

JUMPER RH, RC FOR SINGLE TRANSFORMER.

1
M2903

Fig. 44. Schematic and hookup of T874A,B,C,D,E,F with Q674B. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2

RH
HEAT RELAY 1

3
W1

1
FAN
SWITCH

H1
FALL

1
HEAT RELAY 2

AUTO

W2

H1 ANTICIPATOR
HEAT CHANGEOVER
VALVE

ON
B

4

X1

H2
6
FALL

H2 ANTICIPATOR

SYSTEM
SWITCH

O
COOL CHANGEOVER
VALVE

8
HEAT
C1

RISE

G

OFF
9

FAN RELAY

2

COOL

Y2
COMPRESSOR
CONTACTOR 2

10
C1 ANTICIPATOR
Y1
C2 ANTICIPATOR

RISE

11

C2

RC
1

2

COMPRESSOR
CONTACTOR 1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
JUMPER RH, RC FOR SINGLE TRANSFORMER.

3

OPTIONAL LED ON SOME MODELS.

Fig. 45. Schematic and hookup of T874C,D with Q674B. Used in standard applications.

60-2485—8

96

L2
L1
(HOT)
1
M933C

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

HEAT RELAY 1
W1

1
FAN
SWITCH

H1
FALL

HEAT RELAY 2

AUTO

W2

H1 ANTICIPATOR
ON

HEAT CHANGEOVER
VALVE
B

4
H2

L1
(HOT)
L2
1

R
6
H2 ANTICIPATOR

FALL

SYSTEM
SWITCH

O
COOL
CHANGEOVER
VALVE

8
HEAT

C1

RISE

OFF
G

9

COOL
FAN RELAY
Y2

10
C1 ANTICIPATOR
C2 ANTICIPATOR

COMPRESSOR
CONTACTOR 2
Y1

11

COMPRESSOR
CONTACTOR 1

C2

RISE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M2904

Fig. 46. Schematic and hookup of T874A,B,D with Q674B. Used in standard applications.
.
SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

O
1
H1/C1
ANTICIPATOR

FAN
SWITCH

COOL CHANGEOVER
VALVE

AUTO
G

2

H1

C1

ON

FAN RELAY

FALL
3
L1
(HOT)

R
4

L2

SYSTEM
SWITCH

1

HEAT
5

W1
OFF

AUX. HT.
RELAY

COOL
H2
6

FALL

Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

M2906

Fig. 47. Schematic and hookup of T874R with Q674B. Used in heat pump applications.

97

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1
(HOT)
L2
1

HEAT RELAY 1
W1

1
H1

FAN
SWITCH

FALL

FAN RELAY
G

AUTO

H1 ANTICIPATOR

ON

EXTERNAL
FAN SWITCH

4
RC
H2
H2
ANTICIPATOR

FALL

HEAT RELAY 2

6

W2
8

HEAT CHANGEOVER
VALVE

C1

RISE

9

B

SYSTEM
SWITCH

L2

RH
HEAT

10

OFF

C1 ANTICIPATOR
COOL
C2 ANTICIPATOR

RISE

2
X1

L1
(HOT)
1

FILTER
LED (RED)
O
COOL CHANGEOVER
VALVE

11

C2

Y1
COMPRESSOR
CONTACTOR 1

1

2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

Y2
COMPRESSOR
CONTACTOR 2

CLOGGED FILTER, SERVICE SWITCH.

Fig. 48. Schematic and hookup of T874D with Q674B. Used in standard applications.

60-2485—8

98

M2905

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

H1
ANTICIPATOR

HEAT RELAY 1
1

W1

H2
FAN SWITCH

HEAT
LED (RED)

FALL
AUTO

BLOWER RELAY
G

4

ON

H2 ANTICIPATOR
L1
(HOT)
L2
1

R
6

HEAT RELAY 2

FALL
H1

W2
SYSTEM
SWITCH

8
C1 ANTICIPATOR

HEAT
9

T

OFF
COOL LED
(YELLOW)

COOL
C1

1

Y1

10

RISE

COMPRESSOR
CONTACTOR

LO SPEED
LED (GREEN)

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

L

HSII
CONTROL
PANEL

C
HI SPEED
LED (GREEN

L1
(HOT)
L2

H

M5945

Fig. 49. Schematic and hookup of T874C with Q674B. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

O

1
H1
ANTICIPATOR

2

FALL

H1

COOL CHANGEOVER
VALVE

FAN
SWITCH

Y

AUTO

4

COMPRESSOR
CONTRACTOR

ON
FALL
H2

G
H2 ANTICIPATOR

AUX. HT. RELAY
6
SYSTEM
SWITCH

8

CO

FAN RELAY

W2

L2

RISE

HEAT
9
C1 RISE

OFF

C1 ANTICIPATOR

R
1

L1
(HOT)

COOL
10

M8000

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 50. Schematic and hookup of T874G with Q674B. Used in heat pump applications.

99

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
HEAT RELAY 1

FALL
W1

H1
1
H1 ANTICIPATOR

FAN
SWITCH

FAN RELAY
G

3

AUTO
L1
(HOT) 1
L2

ON
RC
4

2

HEAT RELAY 2

W2

6
FALL

HEAT CHANGEOVER VALVE

H2 ANTICIPATOR

H2

B
8

3

SYSTEM
SWITCH

RH

C1

HEAT
RISE
9

COOL CHANGEOVER VALVE
O

OFF
3
COOL

C1 ANTICIPATOR

COMPRESSOR CONTACTOR 1

10

Y1

C2 ANTICIPATOR

RISE

COMPRESSOR CONTACTOR 2
11

Y2

C2

1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FIELD WIRE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

3

B, O TERMINALS ON SOME MODELS.

L1 L2
(HOT)
M5944

Fig. 51. Schematic and hookup of T874D with Q674B. Used in standard applications.
SUBBASE

THERMOSTAT

H1 ANTICIPATOR
H1

1

SYSTEM COMPONENTS

W1
FAN SWITCH
HEAT RELAY 1

AUTO

FAN RELAY

G
FALL

ON

L1
(HOT)

RC
3

4

1

5

W3

6

W2

H2
FALL

L2

F

H2 ANTICIPATOR
SYSTEM
SWITCH

2

HEAT RELAY 2

RH

HEAT

B
OFF
8
COOL
C1 RISE
9

O

C1 ANTICIPATOR

Y1

COMPRESSOR
CONTACTOR

10
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

OPTIONAL FIELD WIRE JUMPER. W3 AND F TO BE JUMPERED EXCEPT FOR TWO STAGE GAS APPLICATION.

3

FIELD WIRE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

Fig. 52. Schematic and hookup of T874C with Q674B. Used in standard applications.
60-2485—8

100

M5999

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

1

H1
ANTICIPATOR

HEAT RELAY 1
FAN SWITCH

W1

AUTO
FALL

HEAT RELAY 2

H1
ON

4

W2

H2
6
FALL

H2 ANTICIPATOR
8

L1
(HOT)

R

SYSTEM
SWITCH

L2

HEAT
RISE

C1

1

OFF

9

G
COOL

FAN RELAY

10

Y2

C1 ANTICIPATOR

COMPRESSOR
CONTACTOR 2

C2 ANTICIPATOR
11

Y1

C2

RISE

1

COMPRESSOR
CONTACTOR 1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M3202A

Fig. 53. Schematic and hookup of T874D with Q674B. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
1

1
H1 ANTICIPATOR
FALL

C815A THERMISTOR

H1
H2 ANTICIPATOR

2
FAN SWITCH

FALL

L1 (HOT)

R
L2

T

3
AUTO

H3
4
H3 ANTICIPATOR

W1
HEAT RELAY 1

ON
W2

HEAT RELAY 2
5
FALL
H2

6
RESET HEATER

SYSTEM
SWITCH

HEAT RELAY 3
B
HEAT CHANGEOVER VALVE

HEAT

RISE
8

C1

W3

OFF

G
FAN RELAY

COOL

C1 ANTICIPATOR

O

10

COOL CHANGEOVER VALVE

C2 ANTICIPATOR
RISE

11

Y2
COMPRESSOR CONTACTOR 2

C2
1

Y1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

COMPRESSOR CONTACTOR 1
M3674

Fig. 54. Schematic and hookup of T874W with Q674B. Used in standard applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

H1

L1
(HOT)
L2

RH

FALL
3

B

1

H1 ANTICIPATOR

HEAT RELAY 1
NO
FAN
SWITCH

3

H2 ANTICIPATOR

1

W1

4
5
6

FALL

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

HEAT RELAY 2
W2

H2
2

8

NO
SYSTEM
SWITCH

C1
RISE

COMPRESSOR
CONTACTOR 2
Y2

9

COMPRESSOR
CONTACTOR 1

C1 ANTICIPATOR
Y1

10
C2

L2

C2 ANTICIPATOR
RC

L1
(HOT)

RISE
11
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

JUMPER RC, RH FOR SINGLE TRANSFORMER.

3

B AND 5 TERMINALS AVAILABLE ON SOME MODELS.

M3667A

Fig. 55. Schematic and hookup of T874A,D,F with Q674D. Used in standard applications.

SYSTEM COMPONENTS

SUBBASE

RESET
1

FALL

FAN
SWITCH

H1

X
RESET
LED (RED)
FAN RELAY

AUTO
G

H1 ANTICIPATOR
ON
4

R
AUX. HT. RELAY

H2 ANTICIPATOR
W2

6
H2

SYSTEM
SWITCH

FALL

8

B
HEAT
OFF

9
RISE

B RELAY
O

COOL

C1 ANTICIPATOR
C1

L1
(HOT)
L2
1

O RELAY
Y2

10

COMPRESSOR
CONTACTOR 1

11
Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 56. Schematic and hookup of T874C with Q674B. Used in standard applications.

60-2485—8

102

M5975

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

Y
FALL

FAN SWITCH

COMPRESSOR
CONTACTOR

AUTO

1

FAN RELAY

G
L1
(HOT)

ON
R

2

H2

CLOSED-DAY
OPEN-NITE

H1 ANTICIPATOR
3

1

B
L

4

SYSTEM
SWITCH

5

OVERRIDE
HEAT

6
CO

L2

B RELAY

S

JUMPER

OFF

RISE
H1

2
COOL

8

P
COOL CHANGEOVER
VALVE
W

9
RISE
C1

C1 ANTICIPATOR
T

10
1

POWERSUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

JUMPER HONEYWELL SUPPLIED, FIELD INSTALLED.

M8004

Fig. 57. Schematic and hookup of T874P with Q674B. Used in heat pump applications.

THERMOSTAT

H1 ANTICIPATOR
H1

SUBBASE

2

Y

3

FALL

H2 ANTICIPATOR

ECONOMIZER
PACKAGE

NO FAN
SWITCH

4

FALL

SYSTEM COMPONENTS

6

RH

Y

O

O

W

W2

H2
8
RISE

NO SYSTEM
SWITCH
B

9
C1 ANTICIPATOR
CO

10

RC

O
CONTROL
PANEL

C1

M3722

RISE

Fig. 58. Schematic and hookup of T874G with Q674D. Used in standard applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

H1
ANTICIPATOR

SUBBASE

SYSTEM COMPONENTS

1

W1
SYSTEM
SWITCH
HEAT

HEAT
RELAY 1

OFF
4

B
1

COOL

FALL
FAN
SWITCH

8

G1

RISE
C1

L1
(HOT)
L2

R

H1

LO

9

MED

C1
ANTICIPATOR

L1

G2

HIGH

10

L2
K1 RELAY
K1

K1

K2 RELAY
K2

O

ON

HI

K2

K2

MED

LO

Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

3 SPEED FAN
SCHEMATIC

M3729

Fig. 59. Schematic and hookup of T874A with Q674Q. Used in fan coil applications.

SUBBASE

THERMOSTAT

H1 ANTICIPATOR

1

SYSTEM COMPONENTS

W1
FAN
SWITCH
AUTO

FALL

L1
(HOT) L2

1

COOL RELAY
CONTACT
FAN RELAY
G

ON
H1
4
R
6

FALL

H2 ANTICIPATOR
H2

SYSTEM
SWITCH

ELEC. HT. RELAY
W2

EVAP

CHANGEOVER
VALVE

8
COOL
OFF
RISE

9

B
COMPRESSOR
CONTACTOR

HEAT

C1

Y1
C1 ANTICIPATOR

EVAPORATOR
RELAY

10
1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

Y2

Fig. 60. Schematic and hookup of T874C with Q674N. Used in evaporative cooler applications.

60-2485—8

104

M2863

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

COMPRESSOR
CONTACTOR

FALL
Y1
H1

1
FAN RELAY

H1 ANTICIPATOR

FAN
SWITCH

G

4
AUTO
1

ON
FALL

H2
ANTICIPATOR

L1
(HOT)

R
6

L2

H2

ELEC. HT. RELAY
W2

RISE

8

EVAPORATOR
RELAY

SYSTEM
SWITCH
C1

Y2

EVAP.
9

COOL

CHANGEOVER
RELAY

OFF

C1
ANTICIPATOR

1

O

HEAT

10

M2862

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 61. Schematic and hookup of T874C with Q674N. Used in evaporative cooler applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

FAN SWITCH
FAN RELAY
AUTO
G

FALL

ON

H2
1

W2

H2 ANTICIPATOR

AUX. HT. RELAY
R

4

YELLOW
C

FALL
H1

SYSTEM
SWITCH

WOOD/COAL
RELAY

GREEN

8

W1
HEAT

COMPRESSOR
CONTACTOR

9
OFF
X2
COOL

H1 ANTICIPATOR

EXTERNAL COOLING
THERMOSTAT
(SUCH AS T87 F)

10

X1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

Y

R

L2
L1
(HOT)
1

M3723A

Fig. 62. Schematic and hookup of T874F with Q674B. Used in wood/coal applications.

105

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

H2

SUBBASE

SYSTEM COMPONENTS

AUX. HT. RELAY

NO FAN
SWITCH

FALL
1

W2

1

H2 ANTICIPATOR

L1
(HOT)

R
NO
SYSTEM
SWITCH

4
FALL
H1

YELLOW

L2
C

HEAT/COOL
SWITCH

GREEN

8

W1
WOOD/COAL
RELAY

9
H1 ANTICIPATOR
10

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

1

M3725

Fig. 63. Schematic and hookup of T874F with Q674D. Used in wood/coal applications.

THERMOSTAT

SYSTEM COMPONENT

SUBBASE

1

HEAT RELAY 1

H1
ANTICIPATOR

H1

W1

B

SYSTEM
SWITCH
HEAT
2

B RELAY

OFF

FALL

1

COOL

2

3

L1
(HOT)
L2

R
4

C1
ANTICIPATOR

K1 RELAY

FAN
SWITCH

5

L2

G1

MED
K2 RELAY

HIGH

C1

K1

K1

G2

ON

RISE

L1

LO

O RELAY
K2

O

K2

K2

COMPRESSOR CONTACTOR
Y1

LO

HI
MED

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

SINGLE SETPOINT LEVER AND BIMETAL.

3-SPEED FAN SCHEMATIC
M8005

Fig. 64. Schematic and hookup of T874A with Q674Q. Used in fan coil applications.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1

W1
NO. 1 HEAT RELAY

AUTO
FAN
SWITCH
ON

W2

H1 ANTICIPATOR
B

4

HEAT DAMPER

6

FALL
H1

L1
(HOT)
L2

RH

8

L1
(HOT)
L2
1

RC

9
RISE
C1

COOL DAMPER

SYSTEM
SWITCH
HEAT

O

OFF

G

10

FAN RELAY

C1
ANTICIPATOR

COOL
11

Y2
NO. 1 COMP. RELAY
Y1
FILTER
LED (RED)
X1
SERVICE LED
(YELLOW)
X2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

1

M5976

Fig. 65. Schematic and hookup of T874A with Q674B. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
HEAT RELAY 1

H1 ANTICIPATOR

1

W1
NO FAN
SWITCH

HEAT RELAY 2

4
FALL

H1

W2
5

H2

L1
(HOT)
L2
1

RH

6

FALL

NO SYSTEM
SWITCH

H2 ANTICIPATOR
8
9

RC

10

Y2

11

Y1

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

L1
(HOT)
L2
1

M7011

Fig. 66. Schematic and hookup of T874A,D,F with Q674D. Used in standard applications.

107

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

1

X
FAN RELAY

FAN SWITCH
2

H1
C1

G

AUTO

H1/C1 ANTICIPATOR
L1
(HOT)

ON

FALL

3

R

L2

1

4
HEAT CHANGEOVER
VALVE

5

SYSTEM
SWITCH

B

FALL
W2

H2
HEAT

AUX. HT. RELAY

6
OFF
COOL

COMPRESSOR
CONTACTOR
Y

1

M5998

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 67. Schematic and hookup of T874R with Q674B. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

1

Y

H1
ANTICIPATOR

3

H2

COMPRESSOR CONTACTOR

2

G

FALL
3

FAN
SWITCH

FAN RELAY
C

4
CLOSED-DAY
OPEN-NITE

AUTO

5

ON

RISE
CO
H1

SYSTEM SWITCH

RISE

L1
(HOT)

R
OVERRIDE
LED (RED)

6
8

C1

L2

SERVICE
LED (RED)

1

B
B RELAY

L

OVERRIDE

X
9

HEAT
S
OFF

C1 ANTICIPATOR
10

COOL

JUMPER

1 POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.
2

JUMPER HONEYWELL SUPPLIED, FIELD INSTALLED.

3

H2 MAKE OFFEST 8˚ F BELOW H1 MAKE.

COMPRESSOR
FAULT

P

2

COOL CHANGEOVER VALVE

W
T
M101A

Fig. 68. Schematic and hookup of T874P with Q674B. Used in heat pump applications.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

FAN SWITCH
LO
AUTO
HI

Z RELAY
Z

CONT.
G

SYSTEM SWITCH

FAN RELAY
OFF
COOL

RISE

R

8
C1

L1
(HOT)
L2

1

9
COOL RELAY

10
Y

C1 ANTICIPATOR
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M107A

Fig. 69. Schematic and hookup of T874V with Q674R. Used in fan coil applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

1
SERVICE
LED (RED)

NO FAN
SWITCH

H1 FALL

S
COMPRESSOR
FAULT

4
6

W2
SYSTEM
SWITCH

H2
FALL
8

9

AUX. HT. RELAY
1

HEAT

L2

COOL

R

L1
(HOT)

Y
H1
FALL

1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

M1402A

Fig. 70. Schematic and hookup of T874C with Q674S. Used in heat pump applications.

109

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

1

H1
ANTICIPATOR

FAN SWITCH
AUTO

HEAT RELAY 1

3

ON
FALL

L1
(HOT)
L2
1

RH

CHECK

W1

H1

HEAT RELAY 2

4
W2

H2
6
FALL

H2 ANTICIPATOR

SYSTEM
SWITCH

X1

8
HEAT
RISE

G

AUTO

C1

9

FAN RELAY

2

COOL
10

Y2

C1 ANTICIPATOR
COMPRESSOR
CONTACTOR 2
Y1

C2 ANTICIPATOR
11
C2

RISE

RC
1

2

COMPRESSOR
CONTACTOR 1

L1
(HOT)

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
JUMPER RH, RC FOR SINGLE TRANSFORMER.

3

L2

1

OPTIONAL LED ON SOME MODELS.

M932B

Fig. 71. Schematic and hookup of T874A-D with Q674A. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2

RH
H1 ANTICIPATOR

1
FAN
SWITCH

H1

2

4

1
HEAT RELAY 1

AUTO

FALL

W1

W2

ON

HEAT RELAY 2
B

6

HEAT DAMPER

3

H2 ANTICIPATOR

O

H2

FALL

COOL DAMPER
8

RISE

SYSTEM
SWITCH

G

OFF

FAN RELAY

C1
9

AUTO
Y2

C1 ANTICIPATOR
10

COMPRESSOR
CONTACTOR 2
Y1

C2 ANTICIPATOR
11
C2

RISE

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 1

2
RC

1
L2
L1
(HOT)

2 JUMPER TERMINALS RC-RH FOR SINGLE SYSTEM TRANSFORMER ONLY.
M5122A

3 B,O TERMINALS ON SOME MODELS.

Fig. 72. Schematic and hookup of T874D,E,F with Q674C. Used in standard applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

H ANTICIPATOR
Y1

2
H1
FALL

REVERSING
VALVE RELAY

3
Y2

COMPRESSOR
CONTACTOR

FAN SWITCH

4

AUTO

SETBACK

G
ON

FALL

FAN RELAY

6
8

CO

L2

SYSTEM
SWITCH

9

OPEN-NIGHT
CLOSED-DAY

OFF

RISE

1

L1
(HOT)

R

10

AUTO

SETBACK
RELAY

C ANTICIPATOR
C1

L

RISE
1

M7008

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 73. Schematic and hookup of T874G with Q674C. Used in heat pump applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

2

H1
ANTICIPATOR
FALL

Y1
COOL CHANGEOVER
VALVE

3

H1

FAN SWITCH
4

FAN RELAY
AUTO
G
ON
R

8

Y2

SYSTEM
SWITCH
OFF

COMPRESSOR
CONTACTOR
B

RISE
C1
ANTICIPATOR

9

AUTO

CO
10

O
2

RISE
C1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2

SERVICE LED ON SELECT MODELS.

L2
L1
(HOT)

1

X

SERVICE LED
(YELLOW)

COMPRESSOR
FAULT
C
M3680A

Fig. 74. Schematic and hookup of T874H with Q674C. Used in heat pump applications.

111

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

1

H1
ANTICIPATOR

W1
SYSTEM SWITCH
OFF

FILTER LED
(YELLOW)

HEAT RELAY
3
X

AUTO
4
8

A

SERVICE
LED (RED)

FAN SWITCH

H1 FALL

FAN RELAY

AUTO

1

G
ON

L1
(HOT)
L2

R
2

RISE
9

O

C1
ANTICIPATOR

C1

MOMENTARY
CIRCUIT

O
10
Y

COMPRESSOR CONTACTOR
11

T
EXTERNAL
TEMP.
READOUT

THERMISTOR
12

T

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

MOMENTARY POSITION. SPRING RETURN TO "ON" UPON SWITCH RELEASE.

3

FILTER LED ON SELECT MODELS.

M5731

Fig. 75. Schematic and hookup of T874A with Q674C. Used in standard applications.

SUBBASE

THERMOSTAT

H1 ANTICIPATOR

1

SYSTEM COMPONENTS

W1

FAN
SWITCH

HEAT RELAY 1

AUTO
FALL

H1

4

FALL

HEAT RELAY 2

W2
HEAT CHANGEOVER
VALVE

ON

B
L2
1
L1
(HOT)

RH

6
H2 ANTICIPATOR

H2

L1
(HOT)

RC
8
C1
O

SYSTEM
SWITCH
RISE
9

OFF

10

AUTO

COOL CHANGEOVER
VALVE

L2 1

G
FAN RELAY
Y2

C1 ANTICIPATOR
RISE

11

C2

3
C2 ANTICIPATOR

2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

FOR T874C, DELETE C2.

FILTER
LED (YEL)
SERVICE
LED (RED)

Y1

COMPRESSOR
CONTACTOR 2

COMPRESSOR
CONTACTOR 1

X
A

3 FILTER LED ON SELECT MODELS.

Fig. 76. Schematic and hookup of T874A-D with Q674C. Used in standard applications.

60-2485—8

112

M7025

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

1
FALL

FAN
SWITCH

SYSTEM COMPONENTS

RESET
LED (RED)

X1
FAN RELAY

AUTO

CO

G

3
ON
FALL

H2

L1
(HOT)
L2 1

RH
4
2

FALL

6
HEAT CHANGEOVER
VALVE

H1
H1 ANTICIPATOR

W1
HEAT RELAY 2
W3

8

HEAT RELAY 1

RISE

SYSTEM
SWITCH

C1
9

W2
"B" RELAY

OFF
B

C1
ANTICIPATOR
10
1

2

AUTO
L1
(HOT)
1
L2

RC

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

"O" RELAY
O

JUMPER RH AND RC FOR SINGLE
TRANSFORMER SYSTEM.

COMPRESSOR
CONTACTOR

Y1
M4729

Fig. 77. Schematic and hookup of T874K with Q674C. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

Y
1
FALL

H2

FAN
SWITCH

COMPRESSOR
CONTACTOR

AUTO
2
H1
ANTICIPATOR

G
ON
FAN RELAY
C

3
4

SETBACK
CONTACT

5
6
CO

SYSTEM
SWITCH

8

1

HEAT
CHANGEOVER
VALVE

AUTO

RISE

L2

B

OVERRIDE

H1

L1
(HOT)

R

L
OFF

C1

9

S

JUMPER 2

10

P

REVERSING
VALVE

C1
ANTICIPATOR

RISE
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

JUMPER HONEYWELL SUPPLIED, FIELD INSTALLED.

W
M7026

Fig. 78. Schematic and hookup of T874P with Q674C. Used in heat pump applications.

113

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SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
RESET

FAN
SWITCH

1

H1 ANTICIPATOR

X

RESET
LED (RED)

G

AUTO
FALL

H1

FAN RELAY

ON

4

H2

2

FALL

SETBACK
CONTACT

L2
1

R2

3
8

COOL
CHANGEOVER
VALVE

9
CO

SYSTEM
SWITCH
C1
ANTICIPATOR

RISE

RISE

O

OFF
10

C1

L1
(HOT)

R1

6

COMPRESSOR
CONTACTOR

AUTO

Y

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

SETBACK CONTACT ON Q674C1124.

3

H2 ON T874G.

M7027

Fig. 79. Schematic and hookup of T874G,H with Q674C. Used in standard applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

W1
FALL
HEAT
RELAY 1

1
H1
Y1

H1 ANTICIPATOR
4

FAN SWITCH
AUTO
G
ON

FAN RELAY

RC
H2 ANTICIPATOR
H2

CONTACTOR
COMPRESSOR 1

2
6

FALL

SYSTEM
SWITCH
8

HEAT RELAY 2

W2
OFF

L1
(HOT)
L2
1

RH
HEAT

RISE
AUTO

C1
9

C
SERVICE
LED (RED)

COOL

Z

C1 ANTICIPATOR
10

COMPRESSOR
FAULT

C2 ANTICIPATOR
11

C2
RISE

COMPRESSOR
CONTACTOR 2

Y2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

OPTIONAL FIELDWIRE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

M5997

Fig. 80. Schematic and hookup of T874D with Q674E. Used in standard applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

CHANGEOVER
RELAY

FALL
H1
1

W1
B

4

FAN
SWITCH

FAN
RELAY

AUTO

FALL

G
H2 ANTICIPATOR

6

ON

H2

R
8

SYSTEM
SWITCH

RISE

C1

OFF

9

COMPRESSOR
CONTACTOR

W2
Y1

AUTO
C1 ANTICIPATOR

10
1

1

POWER SUPPLY. PROVIDE DISCONECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

L1 L2
(HOT)

M5981

Fig. 81. Schematic and hookup of T874C with Q674C. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2
1

RH
FALL
H1

HEAT RELAY 1

1
H1 ANTICIPATOR

W1

FAN
SWITCH
AUTO

2
HEAT RELAY 2

ON

4

W2

H2 ANTICIPATOR

O

6

FALL

3

H2
8
RISE

SYSTEM
SWITCH

FAN RELAY
G

OFF

C1

B

9
C1
ANTICIPATOR

COMPRESSOR
CONTACTOR 2

HEAT
10

AUTO

Y2
COMPRESSOR
CONTACTOR 1

COOL
C2 ANTICIPATOR
11
1
C2
RISE

Y1
L2

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

2

JUMPER RC, RH FOR SINGLE TRANSFORMER.

3

O AND B TERMINALS ON SELECTED MODELS.

1
RC

L1
(HOT)
M934

Fig. 82. Schematic and hookup of T874A,C,D with Q674E. Used in standard applications.

115

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)

1

L2
H1 ANTICIPATOR

HEAT RELAY 1
W1

1
FALL

COMPRESSOR
CONTACTOR 1

H1
Y1

FAN
SWITCH
AUTO

4

FAN RELAY
G

H2 ANTICIPATOR
ON

RC
FALL

HEAT RELAY 2
6

H2

W2

8

RISE

RH

C1

OFF
9

CHECK LED
(RED)

HEAT

X1
COMPRESSOR
CONTACTOR 2

AUTO

C1 ANTICIPATOR
10

Y2

COOL
C2 ANTICIPATOR
11

L2

RISE

1

C2

POWER SUPPLY. PROVIDE DISCONECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

1

L1
(HOT)
M5982

Fig. 83. Schematic and hookup of T874G with Q674C. Used in standard applications.

THERMOSTAT

SUBBASE

1

SYSTEM COMPONENTS

R

H1 ANTICIPATOR

COOL
CHANGEOVER
VALVE
2

OUTDOOR
FAN RELAY

FAN
SWITCH
FALL

H1

DEFROST
SWITCH

AUTO

DEFROST
RELAY

4
ON

M
HIGH PRESSURE
SWITCH

COMPRESSOR
CONTACTOR

H2 ANTICIPATOR
6

F
DEFROST
RELAY

FALL

H2

FAN RELAY

8
SYSTEM
SWITCH

C1 ANTICIPATOR
9

CO
RISE

V

OFF
DEFROST
RELAY

HEAT

AUX. HT.
RELAY

Y

AUTO
10
COOL

L2

RISE
C1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

L1
(HOT)

Fig. 84. Schematic and hookup of T874G with Q674E. Used in heat pump applications.

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116

1
M4666

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

HEAT RELAY 1
H1
ANTICIPATOR

H1

1

W1
COMPRESSOR
CONTACTOR 1

FALL

Y1

FAN
SWITCH

4

FAN RELAY

AUTO
G

6

ON

FALL

L1
(HOT)

R

H2 ANTICIPATOR

L2

H2
8

1

SYSTEM
SWITCH

RISE

C1

OFF
9

HEAT
HEAT RELAY 2
AUTO

C1
ANTICIPATOR

W2

COOL

10

COMPRESSOR
CONTACTOR 2

C2 ANTICIPATOR
RISE

11
1

C2

Y2

POWER SUPPLY. PROVIDE DISCONECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M5983

Fig. 85. Schematic and hookup of T874A-D with Q674E. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2

1

H1 ANTICIPATOR
R

1

2
FALL

FAN
SWITCH
AUTO

COOL
CHANGEOVER
VALVE

D. F. O.

DEFROST
SWITCH

DEFROST
RELAY

H1
3

H2

ON

M

5

FALL

HIGH
PRESSURE
SWITCH

6
H2 ANTICIPATOR

COMPRESSOR
CONTACTOR

F
8

C1 ANTICIPATOR
RISE

9

SYSTEM
SWITCH

FAN RELAY
V

OFF

DEFROST RELAY
CONTACT

HEAT

Y

AUTO

DEFROST RELAY
CONTACT

CO
10

AUX. HT. RELAY

1

COOL
C1

L2

RISE

VR
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

M4667

L1
(HOT)

Fig. 86. Schematic and hookup of T874G with Q674E. Used in heat pump applications.

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THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

W1

1

HEAT RELAY 1
FALL

H1

Y1
FAN
SWITCH

H1 ANTICIPATOR

COMPRESSOR
CONTACTOR 1

AUTO
G
ON

4

FAN RELAY
L1
(HOT)
L2

RC
H2 ANTICIPATOR

1

FALL
W2

6

H2

HEAT RELAY 2

SYSTEM
SWITCH

B

2

RISE
OFF

8

RH
HEAT

C1

L2
1
L1
(HOT)

X
AUTO

SYSTEM
FAULT CONTACT

9
COOL

C1 ANTICIPATOR
RISE

C
10

C2 ANTICIPATOR
11

C2

COMPRESSOR
CONTACTOR 2

LOCKOUT LED
(RED)
Y2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FIELDWIRE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

M4668

Fig. 87. Schematic and hookup of T874D with Q674E. Used in standard applications.

THERMOSTAT

SUBBASE

1
H1
ANTICIPATOR
FALL

H1

SYSTEM COMPONENTS

W1
FAN
SWITCH

HEAT RELAY 1
G

AUTO
4

1

FAN RELAY

ON

L1
(HOT)
L2

RC

FALL

H2 ANTICIPATOR
W2

6

H2

HEAT RELAY 2

SYSTEM
SWITCH
RISE
8
C1

OFF
RH
HEAT

L2
1
L1
(HOT)

AUTO
9
COOL

C1 ANTICIPATOR
RISE

X
HIGH LED (RED)

10
C2 ANTICIPATOR

C2

1

11

Y2
COMPRESSOR
CONTACTOR 2

LOW LED (GREEN)

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 1

Y1

Fig. 88. Schematic and hookup of T874B,D with Q674E. Used in standard applications.

60-2485—8

118

M4669

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

B
H1 ANTICIPATOR

HEAT
RELAY 1

1

HEAT CHANGEOVER
VALVE

W1
FAN
SWITCH

FALL

H1

AUTO

COMPRESSOR
CONTACTOR 1

ON

4

Y1

6

G

FAN RELAY

H2

FALL
8
C1

HEAT RELAY 2

SYSTEM
SWITCH

9

AUTO

10

COOL

L2
X

SERVICE
LED (RED)

11

Y2

C2 ANTICIPATOR

COOL CHANGEOVER
VALVE

O
1

1

COMPRESSOR
CONTACTOR 2

A

C1 ANTICIPATOR

RISE

1

L1
(HOT)

RH
FILTER
LED (YEL)

HEAT

RISE

L2

W2

OFF

C2

L1
(HOT)

RC

H2 ANTICIPATOR

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M7023

Fig. 89. Schematic and hookup of T874D with Q674E. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

FILTER LED (YEL)
X2
H1 ANTICIPATOR

SERVICE
LED (RED)

1

A2
HEAT RELAY 1

H1

W1

FALL
4

FILTER
LED (YEL)

NO FAN
SWITCH

X1
SERVICE
LED (RED)

5

A1

6
W2
T RELAY

H2 ANTICIPATOR

HEAT RELAY 2
T

FALL

H2

7

L1
(HOT)

RC
8

HEAT
CHANGEOVER
VALVE

SYSTEM
SWITCH
OFF

C1

L2
1

B

RISE

L1
(HOT)

AUTO
9

RH
COOL
CHANGEOVER
VALVE

10
C1 ANTICIPATOR

L2

1

COMPRESSOR
CONTACTOR 2

O
11
Y2

C2

RISE

C2 ANTICIPATOR
12

COMPRESSOR
CONTACTOR 1

Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M7022

Fig. 90. Schematic and hookup of T874D with Q674G. Used in standard applications.

119

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

H1
ANTICIPATOR
FALL

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

1

L1
(HOT)
L2

RH

NO FAN
SWITCH

HEAT RELAY 1
W1

H1

1
HEAT RELAY 2

4
W2

H2
6
FALL

H2 ANTICIPATOR

SYSTEM
SWITCH

B

8

HEAT DAMPER
OFF

RISE

O

AUTO

C1

9

COOL DAMPER

2
Y2

10

COMPRESSOR
CONTACTOR 2

C1 ANTICIPATOR
Y1

C2 ANTICIPATOR
11
C2

RISE

RC
1

2

COMPRESSOR
CONTACTOR 1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

L2
L1
(HOT)
1
M3201B

JUMPER RH, RC FOR SINGLE TRANSFORMER.

Fig. 91. Schematic and hookup of T874A-F,Q with Q674G. Used in standard applications.

THERMOSTAT
H1 ANTICIPATOR

SUBBASE

SYSTEM COMPONENTS

1

W1
NO FAN
SWITCH

3

CHANGEOVER
RELAY

FALL

H1

B
4
W2

H2 ANTICIPATOR

FAN RELAY

6
G
FALL

H2

8

SYSTEM
SWITCH
OFF

9

AUTO

Y1
COMPRESSOR
CONTACTOR

C1

R
1

C1 ANTICIPATOR
RISE

10

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

Fig. 92. Schematic and hookup of T874C with Q674G. Used in heat pump applications.

60-2485—8

120

1
L2
L1
(HOT)
M6008A

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

H1

SUBBASE

SYSTEM COMPONENTS

FALL

HEAT FAN RELAY
1

W1
NO FAN
SWITCH

H1 ANTICIPATOR

HEAT RELAY

4
6
H2
ANTICIPATOR

FALL

H2

W2

SYSTEM
SWITCH
8

RISE
C1

L2 1

OFF
HEAT

COMPRESSOR
CONTACTOR 1

AUTO

Y1

9
C1 ANTICIPATOR
10

L1
(HOT)

RH

COOL
L1
(HOT)

RC

L2
C2 ANTICIPATOR

1

RISE
11

C2

1

Y2
COMPRESSOR
CONTACTOR 2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M4664

Fig. 93. Schematic and hookup of T874D with Q674K. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

B
H1 ANTICIPATOR

1

NO FAN
SWITCH

HEAT CHANGEOVER
VALVE
W1

FALL

H1

HEAT
RELAY 2

4

HEAT
RELAY 1

W2
6

L2 1
RH

L1
(HOT)

H2 ANTICIPATOR
H2

FALL

L1
(HOT)

RC
FILTER
LED (YELLOW)

8
C1

L2 1

X
SYSTEM
SWITCH

RISE
9

OFF
AUTO

SERVICE
LED (RED)

A

COMPRESSOR
CONTACTOR 1

Y1
COMPRESSOR
CONTACTOR 2

10
C1 ANTICIPATOR
Y2
11
C2

COOL CHANGEOVER
VALVE
O

C2 ANTICIPATOR

RISE

"T" RELAY
T
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M7013

Fig. 94. Schematic and hookup of T874D with Q674G. Used in standard applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTATS

SUBBASE

1

SYSTEM COMPONENTS
L1
(HOT)

R
NO FAN
SWITCH

FALL
H1 ANTICIPATOR

L2
1

2
H1
3
OIL RELAY

SYSTEM
SWITCH

4

W2

OFF

OIL LED
(RED)

FALL
WOOD
5

X
WOOD/OIL

H2

WOOD LED
(GREEN)

OIL

H2 ANTICIPATOR

WOOD RELAY

W1
6
1

POWER SUPPLY. PROVIDE DISCONECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M5984

Fig. 95. Schematic and hookup of T874F with Q674K. Used in wood/oil applications.

THERMOSTAT

1

W1

FAN SWITCH

H1

SYSTEM COMPONENTS

SUBBASE

NO. 1 HEAT RELAY

FALL

W2

AUTO

HEAT
DAMPER

NO. 2
HEAT RELAY

ON
B

4
6
FALL
H2 ANTICIPATOR

H2

L2
SYSTEM
SWITCH

RH

L1
(HOT)

8
C1

1

OFF
RC

RISE
AUTO
9

O
FAN RELAY

10

COOL DAMPER
G

C1 ANTICIPATOR
11

Y2

NO. 1 COMPRESSOR
CONTACTOR

Y1
ON LED
(YELLOW)
X
SERVICE
LED (RED)
A
1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION AS REQUIRED.
C

Fig. 96. Schematic and hookup of T874C with Q674C. Used in standard applications.

60-2485—8

122

L2
L1
(HOT)
M104A

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

1
H2

COMPRESSOR CONTACTOR

2

H1
ANTICIPATOR

FALL

Y

3

G
FAN
SWITCH

3
4

CLOSED-DAY
OPEN-NITE

AUTO
ON

5
RISE

FAN RELAY
C
L2
L1
(HOT)

R
OVERRIDE
LED (RED)

6

CO

SERVICE
LED (RED)

1

B

H1
8

SYSTEM SWITCH
L

C1

B RELAY

OVERRIDE

RISE

X
AUTO

9

S
OFF

COMPRESSURE FAILURE
JUMPER

2

P
10
W

C1 ANTICIPATOR
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

JUMPER HONEYWELL SUPPLIED, FIELD INSTALLED.

3

H2 MAKE OFFEST 8˚ F BELOW H1 MAKE.

COOL CHANGEOVER VALVE

M100A

Fig. 97. Schematic and hookup of T874P with Q674C. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

SERVICE
LED (RED)

H1 ANTICIPATOR

1

HEAT RELAY 1

FALL

CHANGEOVER
RELAY

ON

4

B

SYSTEM
SWITCH
8

C1

L2
L1 1
(HOT)

RH

6
H2 ANTICIPATOR

H2

HEAT RELAY 2

W2

AUTO
H1

SYSTEM MONITOR
W1

FAN
SWITCH

FALL

A

L1
(HOT)

RC

OFF
O

CHANGEOVER
RELAY

L2 1

HEAT
RISE
9

G

AUTO

FAN RELAY
10

COOL

Y2

C1 ANTICIPATOR
RISE

11

C2

Y1

COMPRESSOR
CONTACTOR 2

COMPRESSOR
CONTACTOR 1

C2 ANTICIPATOR
2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

T874A IS SINGLE-STAGE (NO W2 OR Y2).

M5106A

Fig. 98. Schematic and hookup of T874D with Q674E. Used in standard applications.

123

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT
H1 ANTICIPATOR

SUBBASE

1

W1

3
OFF
H1

HEAT RELAY 1

SYSTEM
SWITCH

2
FALL

SYSTEM COMPONENTS

HEAT RELAY 2

4

W2
AUTO
W3

5
6

Y2

H2 ANTICIPATOR

4

FALL

H2

7

SERVICE
LED (RED)

FAN
SWITCH

A

AUTO
8
C1
9
RISE

G

L2

ON
C1 ANTICIPATOR

3

FAN RELAY

R
2

1
10

L1
(HOT)

MOMENTARY
CIRCUIT

O

COMPRESSOR RELAY
Y1
5
THERMISTER

1

11

T

12

T

EXTERNAL
TEMP.
READOUT

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

4 H3 OFFSET 12°F FROM H2 FOR NIGHT SETBACK.

2

MOMENTARY POSITION. SPRING RETURN TO "ON" UPON SWITCH RELEASE.

5 THERMISTOR INTERNAL TO THERMOSTAT.

3

H1 AND C1 ARE DPST SWITCHES.

Fig. 99. Schematic and hookup of T874C with Q674C. Used in standard applications.

60-2485—8

124

M531

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

H1 ANTICIPATOR

1

W1

3
OFF
FALL

HEAT RELAY 2

4

W2
AUTO

HEAT RELAY 3
W3

5
FALL
H3

Y2

6

4

H2 ANTICIPATOR
FALL

H2

HEAT RELAY 1

SYSTEM
SWITCH

2
H1

SYSTEM COMPONENTS

FAN
SWITCH

C2
ANTICIPATOR

COMPRESSOR
CONTACTOR 2

SERVICE
LED (RED)
A

AUTO

7

G

3

L2

ON

8

FAN RELAY

R

C1

2
1

9

MOMENTARY
CIRCUIT

RISE
O
C2

L1
(HOT)

COMPRESSOR RELAY
10

RISE

Y1

C2 ANTICIPATOR
5

THERMISTER

11

T

12

T

EXTERNAL
TEMP.
READOUT

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

4 H3 OFFSET 12°F FROM H2 FOR NIGHT SETBACK.

2

MOMENTARY POSITION. SPRING RETURN TO "ON" UPON SWITCH RELEASE.

5 THERMISTOR INTERNAL TO THERMOSTAT.

3

H1 AND C1 ARE DPST SWITCHES.

M532

Fig. 100. Schematic and hookup of T874W with Q674C. Used in standard applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

COOL CHANGEOVER
VALVE
2
H1/C1
ANTICIPATOR

H1
C1

O
AUTO
G
ON

FAN RELAY

FALL

L1
(HOT)
L2

R

FAN SWITCH
3

1

4
W

5

H2
FALL

6
H2
ANTICIPATOR

SYSTEM
SWITCH

X

AUX. HT. RELAY

EM. HT.
LED (RED)

EM. HT.
HEAT

B

OFF
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

COMPRESSOR
CONTACTOR

COOL
Y

M3718A

Fig. 101. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

125

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COMPRESSOR
CONTACTOR

1
H1/C1
ANTICIPATOR

2
H1

F

AUTO

FAN RELAY

ON

C1

HIGH
PRESSURE
INTERNAL
THERMOSTAT SWITCH

M
FAN
SWITCH

FALL

OVERLOAD
SWITCH

V

3
4

FALL

SUPPL. ELEC.
HT. RELAY

EM. HT.
RELAY CONTACT

TIME DELAY
FAN RELAY

Y

5
H2

OUTDOOR
THERMOSTAT

6
2

H2 ANTICIPATOR

EM. HT. RELAY

7

E

SYSTEM
SWITCH

EM. HT.
LED (RED)

EM. HT.
1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

HEAT

X

OFF
VR

2

FIELD WIRE JUMPER TO ALLOW SINGLE
SYSTEM TRANSFORMER.

COOL

COOL CHANGEOVER
VALVE
R

L1 L2
(HOT)

1

L1 L2 1
(HOT)

Fig. 102. Schematic and hookup of T874J,R with Q674L. Used in heat pump applications.

60-2485—8

126

M4726

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER VALVE

1

L1
(HOT)

O

1
H1 ANTICIPATOR

L2

FAN
SWITCH
AUTO

G

ON

2

FAN RELAY

R

OUTDOOR
THERMOSTAT

FALL

H1

4

W2
HEAT RELAY 1

FALL

H2

6

HEAT RELAY HEAT RELAY 2
CONTACT 1

H2 ANTICIPATOR
SYSTEM
SWITCH

E

8

HEAT RELAY
CONTACT 2

2

HEAT RELAY 3

SUPL. HT.
9

L
HEAT

RISE

CO

SUPL. HT.
LED (RED)

OFF

C1 ANTICIPATOR
10

C
COMPRESSOR
CONTACTOR 1

COOL
Y

C1 RISE
1

COMPRESSOR
FAULT

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2

N.O. SWITCH – INSTALLER ADDED, TO LIGHT SUPL. HT. LED
WHEN COMPRESSOR OPERATION IS NOT NORMAL.

M4665

Fig. 103. Schematic and hookup of T874G with Q674L. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

E
2

H1

H1/C1
ANTICIPATOR

C1

EM. HT. RELAY
EM. HT. LED
(RED)

FAN
SWITCH

X

3

FALL

B

AUTO

"B" RELAY

ON
R
4

AUX. HT. RELAY

W2
5

6
FALL

H2

H
L1
(HOT)

SYSTEM
SWITCH

L2

EM. HT.
1

2

COMPRESSOR
CONTACTOR

2

H2 ANTICIPATOR

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

HEAT

OPTIONAL FIELD WIRE JUMPER TO CYCLE
AUXILIARY HEAT RELAY H1 INSTEAD OF
H2 (FASTER RESPONSE).

COOL

1

Y
Y

R
COM

OFF

G

G
R8233B
ELEC. HT.
RELAY

W
O

O

EH
M4728

Fig. 104. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

127

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1
FAN SWITCH

H1 ANTICIPATOR

FAN RELAY
AUTO
G
ON

2

HEAT RELAY 2
W2

H1

FALL
K
L

4
SYSTEM
SWITCH

6
FALL

EM. HT. LED
(RED)

EM. HT.
H2 ANTICIPATOR

EM. HT. RELAY

SYSTEM
MONITOR
SWITCH

IHRI

C

HEAT

H2

R
8

OFF
RHI

COMPRESSOR
CONTRACTOR

COOL
C1 ANTICIPATOR

Y

RISE
10
W1

C1
1

HEAT RELAY 1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

1
M8384

L1 L2
(HOT)

Fig. 105. Schematic and hookup of T874C with Q674L. Used in heat pump applications.

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

COOL CHANGEOVER
VALVE

FALL
2
H1

C1

O
FAN SWITCH

H1/C1
ANTICIPATOR

FAN RELAY
AUTO
G
3

ON

L1
(HOT)
L2 1

R
4
5
6

SYSTEM
SWITCH

HEAT
H2
FALL

H2 ANTICIPATOR

AUX. HT. RELAY

EM. HT.

OFF

W2
EM. HT.
LED
(RED)
X
COMPRESSOR
CONTACTOR

COOL
1

Y

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

EM. HT. RELAY
E

Fig. 106. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

128

M4724

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER
VALVE

2

O

FAN
SWITCH

FAN RELAY
AUTO

H1
ANTICIPATOR

H1

G

FALL

3

ON

OUTDOOR
THERMSTAT

SUPPL. HT.
RELAY

4

H2
ANTICIPATOR

Y1

5

EM. HT.
RELAY CONTACT

H2

COMPRESSOR
CONTACTOR 2

FALL
E

8
SYSTEM
SWITCH

EM. HT. RELAY
COMP.
FAILURE

L

C1 ANTICIPATOR

C1
RISE

10
C2 ANTICIPATOR

EM. HT.
LED (RED)

EM. HT.

C

HEAT

L1
(HOT)

OFF
R

11
COOL
C2

L2

RISE

1

Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 1

M4727

Fig. 107. Schematic and hookup of T874D with Q674L. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

L1
(HOT)
L2
1

R
H1/C1
ANTICIPATOR

H1

2

C1

FAN
SWITCH
FAN RELAY

AUTO

FALL

3

G
ON

4
AUX. HT. RELAY
FALL

5

W

6

AUX. HT.
LED (YELLOW)

H2
H2
ANTICIPATOR

SYSTEM
SWITCH

B
EM. HT.
LED (RED)

EM. HT.

1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

HEAT

X

OFF

O

COOL CHANGEOVER
VALVE

COOL

COMPRESSOR
CONTACTOR
Y

M4725

Fig. 108. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

129

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
AUX. HT. RELAY

1

W
AUX. HT.
LED (GREEN)

2

B

H1
C1
FALL

H1/ C1
ANTICIPATOR
3
FAN
SWITCH
AUTO

EM. HT.
LED (RED)
F
G

4
ON

COMPRESSOR
FAILURE

FAN RELAY

L1
(HOT)
L2
1

R

5
RESET
HEATER

FALL

X2

H2

6

T

OUTDOOR
THERMOSTAT

SYSTEM
SWITCH
COOL
CHANGEOVER
VALVE

EM. HT.
HEAT
1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

OUTDOOR
THERMISTOR

O

OFF
COMPRESSOR
CONTACTOR

COOL
Y

M5071

Fig. 109. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

130

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

RESET
1

L1
(HOT)
L2
1

V
2

2
H1
ANTICIPATOR

VR
INTERNAL
THERMOSTAT

COMPRESSOR
CONTACTOR
M

3
FAN SWITCH

FAN
RELAY

H1

OVERLOAD
SWITCH

HI PRESSURE
SWITCH

AUTO

FALL
4

F
ON

SERVICE
SERVICE
LED (RED)

L
OUTDOOR
THERMOSTAT

SUPL. ELEC.
HT. RELAY

5
S
H2
6

Y

H2
ANTICIPATOR
7

ELEC. HT. RELAY

SYSTEM
SWITCH

E
EM. HT.
LED (YELLOW)

EM. HT.
8
X

HEAT
C1

C1
ANTICIPATOR

TIME DELAY
FAN RELAY

EM. HT. RELAY
CONTACT

3

FALL

C815A OUTDOOR
THERMISTOR

OFF
A

RISE

COOL

COOL CHANGEOVER
VALVE

10
R
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

3 REMOVE FACTORY-INSTALLED S-Y JUMPER TO DISABLE SERVICE LIGHT.
M2854

2 REMOVE FACTORY INSTALLED V-VR JUMPER WHEN
CONNECTING A TWO TRANSFORMER SYSTEM.

Fig. 110. Schematic and hookup of T87C,R with Q674L. Used in heat pump applications.

131

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

V

1
RESET
HEATER

1
L1
(HOT)

2

L2
VR

2
H1/ C1
ANTICIPATOR

COMPRESSOR
CONTACTOR

3

M
FAN
SWITCH

4

INTERNAL
THERMOSTAT

OVERLOAD
SWITCH

AUTO

HIGH
PRESSURE
SWITCH

F
ON

H1

FAN RELAY

C1

SERVICE

L
SERVICE
LED (RED)

FALL

OUTDOOR
THERMOSTAT

5

6

Y
EM. HT.
RELAY
SYSTEM
SWITCH

H2

7

SUPPL. ELEC.
HT. RELAY

E

EM. HT.

X

OFF
A
COOL

C815A
OUTDOOR
THERMISTOR
COOL CHANGEOVER
VALVE

H2
ANTICIPATOR

1

EM. HT.
RELAY

EM. HT. LED
(YELLOW)

HEAT

FALL

EM. HT.
RELAY

R

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

2

REMOVE FACTORY INSTALLED V-VR JUMPER WHEN
CONNECTING A TWO TRANSFORMER SYSTEM.

Fig. 111. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

132

M2851

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

COOL CHANGEOVER
VALVE

FALL
O

2
H1

FAN
SWITCH

C1
H1/C1
ANTICIPATOR

AUTO

FAN RELAY
G
L1
(HOT)

ON
R

3
4

H2
ANTICIPATOR

5

SYSTEM
SWITCH

1
L1

EM. HT.
6

HEAT
OFF

H2

FALL
COOL

EM. HT. LED
(RED)
X
AUX. HT. LED
(GREEN)
AUX. HT. RELAY
W2

1

L2

COMPRESSOR
FAILURE

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

Y
EM. HT. RELAY
E
M8383

Fig. 112. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

133

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2
1

R
HEAT
CONTRACTOR 3

EM. HT. RELAY
H1/C1
ANTICIPATOR

EM. HT. RELAY
1

W3
HEAT
CONTRACTOR 2

OUTDOOR
THERMOSTAT
2
DEFROST RELAY
3

H1

W2

HEAT
CONTRACTOR 1

HIGH LIMIT
SWITCH

B

DEFROST
RELAY

REVERSING
VALVE

C1
FALL
FAN
SWITCH
AUTO
4
ON

H2

FALL

CHECK LED
(GREEN)
L

5

OPTIONAL COMP.
FAILURE DEVICE

X2

H2 ANTICIPATOR

6

SYSTEM
SWITCH

X1
EM. HT.
LED (RED)

EM. HT. RELAY
E

EM. HT.

FAN RELAY
7

HEAT

G

OFF
COOL

COMPRESSOR
CONTACTOR

HIGH
PRESSURE
SWITCH

Y
1

LOW AMBIENT
CUTOFF

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

COOL CHANGEOVER
VALVE

O
M4720

Fig. 113. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

1
RESET
HEATER

M2
OUTDOOR
THERMOSTAT

H1
ANTICIPATOR
2

HIGH SPEED
COMPRESSOR
CONTACTOR

M
3

FAN SWITCH

FAN
RELAY

AUTO

LOW SPEED
COMPRESSOR
CONTACTOR

F

H1

ON

FALL

L1
(HOT)
L2
1

V

4

5

R
2

H2

L

FALL

COOL
CHANGEOVER
VALVE

SERVICE

6
H2 ANTICIPATOR
X
EM. HT. LED
(YELLOW)

7

EM. HT.
RELAY

E
OUTDOOR
THERMOSTAT

8
SYSTEM
SWITCH
RISE

C1

C1
ANTICIPATOR

EM. HT.

SUPPL. ELEC.
HT. RELAY

VR
SERVICE
LED (RED)

HEAT
10
OFF

EM. HT.
RELAY

COOL
RISE

C2

SUPPL. ELEC.
HT. RELAY

Y

C2
ANTICIPATOR

C815A OUTDOOR
THERMISTOR
A
11

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2 REMOVE FACTORY INSTALLED V-VR JUMPER WHEN CONNECTING
A TWO TRANSFORMER SYSTEM.

M2853

Fig. 114. Schematic and hookup of T874D with Q674L. Used in heat pump applications.

135

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
(HOT) L1

L2
1

H1/C1
ANTICIPATOR
R

2

FALL

ODT 1

H1

RTD 1

C1

EHR 1

RTD 2

W3
3

4

FAN SWITCH

ODT 2

AUTO
EHR 2

ON

H2
ANTICIPATOR

W2

5

H2

RTD 3

RTD 1

AUX. HT.
LED
(GREEN)

6

2

FALL

X
EM. HT.
LED (RED)

SYSTEM
SWITCH

SYSTEM
MONITOR

RD

L

FAN RELAY

G

EM. HT.

O

HEAT
OFF

COOL CHANGEOVER
VALVE

E

COOL

EM. HT.
RELAY

CHP

LACO
Y
B

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

AUXILIARY HEAT LED AVAILABLE ON SOME MODELS.

COMPRESSOR
CONTACTOR

M5072A

Fig. 115. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

136

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
H1/C1
ANTICIPATOR
H1

C1

3

FALL

E
FAN
SWITCH

EM. HT. RELAY

AUTO

X

EM. HT.
LED (RED)

ON

B
4
R
AUX. HT. RELAY
5

W2

H2 ANTICIPATOR

6

2

SYSTEM
SWITCH

COMPRESSOR
CONTACTOR

H
L1
(HOT)
L2

EM. HT.
H2
FALL

A

HEAT
COMP. FAULT
LED (YELLOW)

OFF
COOL
1

2

1
Y

Y

G

G

R
COM

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.
OPTIONAL FIELD WIRE JUMPER TO CYCLE
AUXILIARY HEAT RELAY WITH H1 INSTEAD
OF H2 (FASTER RESPONSE).

R8233B
ELEC.
HT. RELAY

W
O

O

EH
M2857

Fig. 116. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

137

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

L1
(HOT)
L2
1

R
DEFROST
RELAY
ENTHALPY
CONTROL RELAY

2

B
FALL

H1

HEAT RELAY
CONTACT 1

H1 ANTICIPATOR

MOTOR
3

G

3

FAN
SWITCH

ECONOMIZER
RELAY

DEFROST
SWITCH

OUTDOOR
FAN RELAY 1

AUTO
4

ON

H2 ANTICIPATOR

ENTHALPY
CONTROL
5

FALL

DEFROST SWITCH
RELAY
TM1

2

TM2
LOW AMBIENT
THERMOSTAT 1

ENTHALPY
CONTROL
RELAY 2

H2

OUTDOOR
FAN RELAY 3

OUTDOOR
FAN RELAY 2

6

1ST STAGE LOW
PRESSURE LIMIT
8
Y1

C1

ENTHALPY
CONTROL
RELAY 1

RISE

1ST STAGE
SHORT
CYCLE
CONTROL

MOTOR
1

2ND STAGE
SHORT
CYCLE
CONTROL

MOTOR
2

TIME DELAY
HEATER

TIME DELAY
Y2
C1 ANTICIPATOR
2ND STAGE LOW
PRESSURE LIMIT

10

DEFROST
RELAY
SYSTEM
SWITCH

C2 ANTICIPATOR

W
EM. HT.
11

LED
(GREEN)

HEAT

OUTDOOR
THERMOSTAT

HEAT
RELAY 1

X
C2
RISE

OFF
SERVICE
COOL
SERVICE
LED (RED)

L

DEFROST
RELAY
COOL CHANGEOVER
VALVE

O
1

2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
OPTIONAL ECONOMIZER HOOKUP (DOTTED LINES).

Fig. 117. Schematic and hookup of T874D with Q674L. Used in heat pump applications.

60-2485—8

138

M7755

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

1

L1
(HOT)
L2
1

R

H1

DEFROST
RELAY
ECONOMIZER
RELAY

FALL
2

B

H2
HEAT RELAY
CONTACT 1
FALL

G

H1
ANTICIPATOR
H2 ANTICIPATOR
3
4
H3
ANTICIPATOR

ECONOMIZER
RELAY
DEFROST
SWITCH

FAN
SWITCH

MOTOR
3

AUTO

OUTDOOR
FAN RELAY 1

ON

DEFROST
RELAY
ENTHALPY
CONTROL

DEFROST SWITCH
RELAY

2

5

TM1

TM2
OUTDOOR
THERMOSTAT 1

FALL

H3
ECONOMIZER
RELAY 2

6

1ST STAGE LOW
PRESSURE LIMIT

8

C1

Y1

RISE

ECONOMISER
RELAY 1

9
SYSTEM
SWITCH
C1 ANTICIPATOR
C2 ANTICIPATOR
10

OUTDOOR
FAN RELAY 3

OUTDOOR
FAN RELAY 2

1ST STAGE
SHORT
CYCLE
CONTROL

MOTOR
1

2ND STAGE
SHORT
CYCLE
CONTROL

MOTOR
2

TIME DELAY
HEATER

TIME DELAY
RELAY

EM. HT.

Y2

HEAT

DEFROST
RELAY

OFF

2ND STAGE LOW
PRESSURE LIMIT

COOL
DEFROST
RELAY
CONTACT

C2
RISE

AUXILIARY
HEAT RELAY

W
DEFROST
RELAY
CONTACT

AUX. HEAT
LED (GREEN)

11

COOL CHANGEOVER
VALVE

O
RESET HEATER
12
X

1

2

EMERGENCY
HEAT RELAY

EM. HEAT
LED (RED)

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

E
C815 OUTDOOR
THERMISTOR

OPTIONAL ECONOMIZER HOOKUP (DOTTED LINES).
A

M7756

Fig. 118. Schematic and hookup of T874W with Q674L. Used in heat pump applications.

139

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1

L1
(HOT)

L2

C815A
OUTDOOR
THERMISTOR

RESET
HEATER
1

T

H2 ANTICIPATOR
W2

2
FAN SWITCH

AUX. HT. RELAY

AUTO
G

ON

3

FAN RELAY
R
X

4
H1
C1
FALL

SERVICE LED
(YELLOW)

SYSTEM
SWITCH

5

SERVICE

Z
EM. HT.
C1
ANTICIPATOR

EM. HT.
LED (RED)

HEAT
6
OFF

K

COOL

FALL
1

H2

11

Y

12

W1

EM. HT. RELAY

COMPRESSOR
CONTACTOR

H1 ANTICIPATOR

HEAT CHANGEOVER
RELAY

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M5955

Fig. 119. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

L1
(HOT)
2
FALL
H1

C1

H1/C1
ANTICIPATOR

FAN SWITCH
1

FAN RELAY
AUTO
3

L2

G

ON
R

4

AUX. HT. RELAY
W

5
FALL

H

H2
6
H2
ANTICIPATOR

B
SYSTEM
SWITCH

"H" RELAY

EM. HT.
LED (RED)
X
EM. HT. RELAY

EM. HT.
T
HEAT

C815A1039
THERMISTOR

OFF
O
COOL

CHANGEOVER VALVE (COOL)

11
Y
RESET HEATER
COMPRESSOR
CONTACTOR

12
1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 120. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

140

M3173B

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

2
H1 ANTICIPATOR

SYSTEM COMPONENTS
L1
(HOT)
L2 1

R
FAN
SWITCH

COMPRESSOR
FAILURE

3

ODT1
AUTO
RTD2

EHR1

H1

ON

FALL
4

ODT2
EM. HT.
LED (RED)

5
H2 ANTICIPATOR

L
RTD1
EHR2

RTD3

X

6

AUX. HT.
LED (GRN)

H2
FALL

RTD1
W2
RD

SYSTEM
SWITCH
8
C1
ANTICIPATOR

COOL CHANGEOVER
VALVE

EM. HT.
HEAT

10

FAN RELAY

G

EM. HT.
RELAY

O

OFF

E

COOL
LACO

C1

COMPRESSOR
CONTACTOR

CHP

Y

RISE

HEAT CHANGEOVER
VALVE
B
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M7012

Fig. 121. Schematic and hookup of T874C with Q674L. Used in heat pump applications.

141

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

FAN
SWITCH

SYSTEM COMPONENTS
FAN RELAY
G

AUTO
2
FALL

L2

ON
R

H1
C1

H1/C1
ANTICIPATOR
3

1

L1
(HOT)

W2
AUX. HT. RELAY
K
EM. HT. RELAY

4
L
CO
SYSTEM
SWITCH
5

FALL

EM. HT.
HEAT

H2

H2
ANTICIPATOR
6

EM. HT. LED
(YELLOW)

OFF

C
SERVICE
LED (RED)

COMPRESSOR
CONTACTOR

COOL
Y
1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

W1
CHANGEOVER
VALVE

Z
SERVICE

Fig. 122. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

142

M8379

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
L2
(HOT)

ODT 1
1
2
H1

C1

EHR 1

H1/C1
ANTICIAPTOR

RTD 2

RTD 1

FALL
3

4

ODT 2
FAN
SWITCH
EHR 2

AUTO

RTD 3

ON
R
5
L
H2
FALL

EM. HT.
LED (RED)

H2
ANTICIPATOR

COMPRESSOR
MONITOR
X

6

AUX. HT.
LED
(GREEN)

RTD 1
W2

8

SYSTEM
SWITCH

RD

EM. HT.
10

FAN RELAY

G
2
COOL
CHANGEOVER VALVE

HEAT
OFF

1

2

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

O

EM. HT. RELAY

COOL
E

CHP

LACO
CONNECT CHANGEOVER
RELAY TO B FOR HEAT
CHANGEOVER, TO O FOR
COOL CHANGEOVER.

Y

B

COMPRESSOR
CONTACTOR

2

HEAT
CHANGEOVER VALVE
M1030A

Fig. 123. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

143

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1

L2

(HOT)
1
FALL

R

FAN
SWITCH

H1
2

AUTO

3

ON

H1
ANTICIPATOR

COMPRESSOR CONTACTOR
Y
G

EM. HT. OR
SUPL. HT.
LED (RED)

5

OUTDOOR
THERMOSTAT

L

H2
6

RISE

8

SYSTEM
SWITCH

9

EM. HT. OR
SUPL. HT.

C1 ANTICIPATOR

CO

2

HEAT RELAY
CONTACT 2

HEAT RELAY 2

HEAT RELAY 3

E

HEAT

X

OFF
COOL

"P" RELAY

"X" RELAY

P

RISE
CO

HEAT RELAY
CONTACT 1

C

10

C1

HEAT RELAY 1

W2

4
H2
ANTICIPATOR
FALL

FAN RELAY

2

11
O
12

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

ON MODELS INCLUDING EXTERNAL JUMPER, W2=W1 AND L=F.

COOL
CHANGEOVER VALVE

Fig. 124. Schematic and hookup of T874J with Q674L. Used in heat pump applications.

60-2485—8

144

M8003

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1
(HOT)

R

L2

L
2
H1/C1
ANTICIPATOR
3

EM. HT.
LED (RED)
3

FAN
SWITCH

C1
FALL

4

2

ON

X

H2
ANTICIPATOR
H2
FALL

AUX. HT.
RELAY

W3

AUTO

H1

1

AUX. HT.
LED (GRN)

6

AUX. HT.
RELAY

W2
SYSTEM
SWITCH
EM. HT.

FAN RELAY
G

HEAT
COOL CHANGEOVER
VALVE

OFF

O

COOL
E
EM. HT. RELAY
Y
COMPRESSOR
CONTACTOR
B
1

"B" RELAY
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

TERMINAL LABELED C/X ON SOME MODELS.

3

W3 TERMINAL AVAILABLE ON SOME MODELS ONLY.

M3683A

Fig. 125. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

145

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER
VALVE

L1
(HOT)
L2
1

O

1
H1 ANTICIPATOR
FAN
SWITCH

FAN RELAY

AUTO
G

2
ON

R

FALL

H1

OUTDOOR
THERMOSTAT

4
W2
FALL

HEAT RELAY 1

6
H2

H2 ANTICIPATOR
HEAT RELAY
CONTACT 1

8

CO

HEAT RELAY
CONTACT 2

2

9

RISE

HEAT RELAY 3

SUPL. HT.
L

10

HEAT
SUPL. HT.
LED (RED)

COOL

RISE

C1

E

SYSTEM
SWITCH

C1 ANTICIPATOR

HEAT RELAY 2

C

Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

N.O. SWITCH INSTALLER ADDED, TO LIGHT EM. HT. LED WHEN COMPRESSOR OPERATION IS NOT NORMAL.

COMPRESSOR
CONTACTOR 1

M4722

Fig. 126. Schematic and hookup of T874G with Q674P. Used in heat pump applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1
(HOT)

R
ODT1
2

L2

RTD1
1

H1 ANTICIPATOR

FALL

EHR1

FAN SWITCH
H1

W3

3
AUTO
ON

W2

H2 ANTICIPATOR
5

H2

8

RTD3

AUX.HT.
LED (GREEN)
X
EM. HT.
COMPRESSOR
LED (RED) FAILURE

HEAT
OFF

L

COOL

G

RISE
C1

EHR2

SYSTEM SWITCH

EM. HT.
6

RTD2

RTD1

4
FALL

ODT2

RD
FAN RELAY

O
COOL CHANGEOVER
VALVE

E

10
C1 ANTICIPATOR

LACO
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

EM. HT.
RELAY

COMPRESSOR
CONTACTOR

B

Fig. 127. Schematic and hookup of T874C with Q674L. Used in heat pump applications.
60-2485—8

CHP

Y

146

M5652A

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

R

H1/C1
ANTICIPATOR
2

FALL

C1

L2

A
1

SERVICE
LED (RED)

FAN
SWITCH

H1

L1
(HOT)

ODT1

RD

EHR1

RTD1

W3

3
AUTO
ON

RTD1

4

ODT2

RTD2

EHR2

RTD3

W2

FALL

H2 ANTICIPATOR
5

AUX. HT.
LED
(GREEN)

SYSTEM
SWITCH

H2

X

EM. HT.
6

EM. HT.
LED
SYSTEM
(YELLOW) MONITOR

HEAT
OFF

RD

L

COOL

FAN RELAY

G
1

POWER SUPPLY. PROVIDE
DISCONNECT MEANS AND
OVERLOAD PROTECTION
AS REQUIRED.

O
COOL CHANGEOVER
VALVE

EM. HT. RELAY

E
LACO

COMPRESSOR
CONTACTOR

CHP

Y
B

M5653A

Fig. 128. Schematic and hookup of T874R with Q674L. Used in heat pump applications.
THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
FAN RELAY

2
FAN AUTO
SWITCH
ON

H1 ANTICIPATOR

H1
FALL

G
L1
(HOT)
1
L2

R

3

4
W

H2 ANTICIPATOR

EM. HT. RELAY
FALL

6
H2

SYSTEM
SWITCH

AUX. HT. RELAY

X

EM. HT.
EM. HT.
LED (RED)

HEAT

B

OFF

RISE

COOL
8

CO

COOL CHANGEOVER VALVE
O

9
C1
ANTICIPATOR

RISE

Y

10

C1
1

COMPRESSOR
CONTACTOR
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M102A

Fig. 129. Schematic and hookup of T874G with Q674L. Used in heat pump applications.

147

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2

O
COOL
CHANGEOVER VALVE

FAN
SWITCH

H1

G

C1
AUTO

FAN RELAY

FALL
ON

L1
(HOT)
L2
1

R

H1/C1
ANTICIPATOR
3

W1
4

5

AUX. HT.
LED
(YELLOW)
SYSTEM
SWITCH

FALL

6

EM. HT. RELAY
E
COMPRESSOR
FAILURE

EM. HT.
H2

2

CHECK
LED
(RED)

HEAT

X

H2 ANTICIPATOR
OFF

C

COOL
11

C815A OUTDOOR
THERMISTOR
SYSTEM
LED (GREEN)

RESET

T

12
1

2

COMPRESSOR
CONTACTOR

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

Y

FACTORY-INSTALLED JUMPER.

Fig. 130. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

148

M1628A

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2
1

H1/C1 ANTICIPATOR
2

AUTO
FAN
SWITCH
ON

R

3
H1

W2

C1

HCR 1
RESET
HEATER

FALL

L

4
SYSTEM
SWITCH

ODT
SUPL. HT.
LED (RED)

SUPL. HT.

FAN RELAY
G

6

HEAT
COOL CHANGEOVER
VALVE

2

H2 ANTICIPATOR
H2

C

FALL

O

COOL

E
HCR 2

HCR 3

Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FOR Q674L1454,

COMPRESSOR
CONTACTOR

IS "OFF".

HCR 1

HCR 2

M4723

Fig. 131. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

O

2
FAN
SWITCH

FALL
H1

C1

COOL CHANGEOVER
VALVE
FAN RELAY

AUTO

H1/C1
ANTICIPATOR

G

ON

L1
(HOT)

R

1

3
L2

3R
4
W1
5

SYSTEM
SWITCH

AUX. HT.
LED
(YELLOW)

EM. HT.
6

H2
H2
ANTICIPATOR

FALL

SEQ 1
2
SEQ 2

HEAT
E

OFF
COOL
EM. HT.
LED
(RED)

EM. HT. RELAY

4R

4R
X
C

SYSTEM
LED
(GREEN)

11

5R

C815A
OUTDOOR
THERMISTOR

4R

HPS

T

12
RESET

Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS.

4R

COMPRESSOR
CONTACTOR

M1858

Fig. 132. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

1
H1/C1
ANTICIPATOR

FAN
SWITCH

FAN
RELAY

G

L1
(HOT)

AUTO
2

H1

SYSTEM COMPONENTS

R

L2 1

ON

C1

K

FALL
W2

EM. HT.
RELAY

AUX. HT.
RELAY

3
L
4

EM. HT.
LED (YEL)

SYSTEM
SWITCH

C

5

COMPRESSOR
FAILURE

EM. HT.
6
H2 ANTICIPATOR
H2
FALL

Z

HEAT

RESET
LED (RED)

OFF

CO

W1 RELAY

W1

COOL

COMPRESSOR
CONTACTOR
Y
1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

Fig. 133. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

150

M2018

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
RTD 1

ODT 1

1
H1

EHR 1

RTD 2

C1
FALL

ODT 2
2
EHR 2

H1/C1
ANTICIPATOR

RDT 3

FAN SWITCH
3
FAN RELAY
AUTO
G
ON
4

L1
(HOT) 1
L2

R

H2
ANTICIPATOR
W2

5
AUX. HT.
LED (GREEN)

RTD 1

EM. HT. RELAY

E
6

FALL

COMP.
FAILURE

H2

L

SYSTEM
SWITCH
8

RD

EM. HT.
LED (RED)

CHANGEOVER
VALVE (HEAT)

EM. HT.
B
HEAT
X

OFF
COOL

LACO

10

COMPRESSOR
CONTACTOR

CHP

Y
CHANGEOVER VALVE (COOL)
O
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

M106A

Fig. 134. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

151

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

FAN
SWITCH

L1
(HOT)

R

AUTO

H1/C1
ANTICIPATOR
2

L2 1

ON

W2
HCR 1

3
H1

C1

L
SUPL. HT.
LED (RED)

RESET
HEATER

FALL

HCR 2

HCR 1

ODT
C

4
SYSTEM
SWITCH

G
FAN RELAY

SUPL. HT.

O

6

COOL
CHANGEOVER VALVE

HEAT
H2 ANTICIPATOR

OFF
E
COOL

H2

HCR 3

HCR 2

FALL

Y
COMPRESSOR
CONTACTOR

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M2017

Fig. 135. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

G

1

FAN RELAY

C1
ANTICIPATOR

W

H1
ANTICIPATOR

FAN
SWITCH

AUX. HT.
LED (GRN)

U

AUX. HEAT
RELAY

1

2
AUTO
3
H1

ON

EM. HT.
LED (RED)

B
F

C1

COMP.
FAILURE
2

4

FALL

L2

RESET

H2
FALL

5

R

6

T

SYSTEM
SWITCH
EM. HT.

X2
O.D.
STAT

HEAT
OFF

FIELD REMOVABLE JUMPER

C815A OUTDOOR
THERMISTOR
COOL CHANGEOVER
VALVE

O

COOL
1

L1
(HOT)

COMPRESSOR
CONTACTOR
Y

2 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

Fig. 136. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

152

M2012

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
RTD 1

ODT 1

EHR 1

1
H1

RTD 2

C1
FALL

ODT 2
2
EHR 2

H1/C1
ANTICIPATOR
3

RDT 3

W3

FAN SWITCH

FAN RELAY
AUTO

G

ON

L1
(HOT) 1
L2

R

4
H2
ANTICIPATOR

W2

5
AUX. HT.
LED (GREEN)

RTD 1

EM. HT. RELAY

E
6

FALL

H2

COMP.
FAILURE
EM. HT.
LED
(RED)

SYSTEM
SWITCH

RD

L
CHECK
LED (RED)

EM. HT.

CHANGEOVER
VALVE (HEAT)

B
HEAT
X

OFF

COMPRESSOR
CONTACTOR

COOL

LACO

CHP

Y
CHANGEOVER VALVE (COOL)
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

O

M105A

Fig. 137. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

153

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1

J
R1 NO2

S1 RELAY

2

S1 NC

H1
S

FALL

FAN SWITCH
H1 ANTICIPATOR

SOLIENOID
RELAY

AUTO
ON

FAN RELAY

G
L1
(HOT)
L2
1

R
3

2

4

C

5

H2

H2 ANTICIPATOR

FALL

AUX. HT. RELAY

H2

SYSTEM SWITCH
HEAT

RISE
8

C1

COMPRESSOR
CONTACTOR

R1 NC1

7
H1

OFF
R2 NO1

COOL
9

REVERSING
VALVE

C1 ANTICIPATOR
10
O
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FIELD REMOVABLE JUMPER

R1 RELAY
M103A

Fig. 138. Schematic and hookup of T874L with Q674B. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1
FAN RELAY
AUTO

H1 ANTICIPATOR

G
2

ON
FAN
SWITCH

R

L1
(HOT)
L2
1

FALL
H1

B

4

H2 ANTICIPATOR

6

SYSTEM
SWITCH

W1
COMPRESSOR
RELAY

AUX. HT.
H2

HEAT PUMP

FALL

8
C1

RISE

2 STG. HEAT
OFF

C1 ANTICIPATOR

HEAT PUMP
LED (GREEN)

COOL

AUX. HT. RELAY

W2
AUX. HT
LED (RED)
C
COOL CHANGEOVER
VALVE

10

O

C2 ANTICIPATOR

Y1
COMPRESSOR
CONTACTOR 1

11
C2

RISE

1

Y2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 2

Fig. 139. Schematic and hookup of T874D with Q674F. Used in heat pump applications.

60-2485—8

154

M4730

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2
1

1
FALL
H1 ANTICIPATOR

T

H1
2

C815A OD THERMISTOR
W3
H2

H2 ANTICIPATOR

FALL

AUX. HT. RELAY

3
AUX. HT.
LED
(GREEN)

FAN SWITCH
AUTO

H3 ANTICIPATOR
4

U

G

ON

FAN RELAY

H3
FALL

EM. HT.
LED (RED)

5

R

E
6
RESET

EM. HT. RELAY

COMPRESSOR
MONITOR

L
CHECK LED
(RED)
RISE

X
8

C1

SYSTEM
SWITCH

B

EM.HT.
2

9
HEAT
C1 ANTICIPATOR

HEAT CHANGEOVER
RELAY
COOL CHANGEOVER
RELAY

OFF

10

O
COOL

COMPRESSOR
CONTACTOR 1

C2 ANTICIPATOR

RISE

C2

11

Y1

12

Y2

COMPRESSOR
CONTACTOR 2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

CONNECT CHANGEOVER RELAY TO 'O' TERMINAL FOR CHANGEOVER IN COOLING OR TO 'B' TERMINAL FOR CHANGEOVER IN HEATING.

M156A

Fig. 140. Schematic and hookup of T874W with Q674L. Used in heat pump applications.

155

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

R
FALL

FAN
SWITCH

1
H1
ANTICIPATOR

H1

W1
FAN RELAY

AUTO
G
ON

4
FALL

HEAT RELAY 2

6

W2

H2
H2
ANTICIPATOR

EM. HT. LED
(RED)

SYSTEM
SWITCH
OFF

X2
EM. HT. RELAY

RISE
EM. HT.

C1

E

8
HEAT

COMPRESSOR
CONTACTOR 2

9
AUTO

C1
ANTICIPATOR

Y2
COOL

COMPRESSOR
CONTACTOR 1

10
C2
ANTICIPATOR

C2
RISE

L1
(HOT)
L2
1

HEAT RELAY 1

Y1
11
M8376

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

Fig. 141. Schematic and hookup of T874C with Q674F. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)

R
FAN
SWITCH

FALL
H1
1
H1 ANTICIPATOR

L2 1

AUTO
W1

ON

HEAT RELAY 1

4
H2 ANTICIPATOR

W2
6

HEAT RELAY 2

B

FALL
H2

X2
CHECK
LED (RED)

SYSTEM
SWITCH
OFF
RISE

X1
E
EM. HT. RELAY

EM. HT.

C1
8

G

HEAT

FAN RELAY

AUTO
9

Y2

COOL

C1
ANTICIPATOR

COMPRESSOR
CONTACTOR 2

10
C2
ANTICIPATOR

Y1
11
O

C2

RISE

COMPRESSOR
CONTACTOR 1
M5985

1

POWER SUPPLY. PROVIDE DISCONECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 142. Schematic and hookup of T874C,D with Q674F. Used in standard applications.

60-2485—8

156

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

1

FALL

Y1

H1 ANTICIPATOR
H1

COMPRESSOR
CONTACTOR

FAN
SWITCH

2

FAN RELAY

AUTO
G

4

ON

FALL

R

L1
(HOT)

6

L2

SYSTEM
SWITCH

H2
H2
ANTICIPATOR

1

OFF
W1

AUTO
8

RISE

AUX. HT. RELAY
C

CO
C1
ANTICIPATOR

AUX. HT. LED
(RED)

9

O
1

10
C1

COOL
CHANGEOVER VALVE

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

M8378

RISE

Fig. 143. Schematic and hookup of T874G with Q674B. Used in heat pump applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1

L2

(HOT)
1
R

FAN
SWITCH

FALL

COMPRESSOR CONTACTOR
Y

H1

AUTO

2

G
ON

FAN RELAY

3
W2

HEAT RELAY 1

H1 ANTICIPATOR

OUTDOOR
THERMOSTAT

4
H2 ANTICIPATOR

SUPP. HT.
LED (RED)
L

5

HEAT RELAY
CONTACT 1

H2 FALL

HEAT RELAY 2

C
6
E
8
RISE

HEAT RELAY
CONTACT 2

9

SYSTEM
SWITCH

X

C1 ANTICIPATOR

CO

"P" RELAY
SUPL. HT.

10

HEAT RELAY 3

"X" RELAY

P

ON
RISE
C1

CO

COOL CHANGEOVER
VALVE

OFF
11

12

O
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
M5956

Fig. 144. Schematic and hookup of T874J with Q674J. Used in heat pump applications.

157

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
(HOT) L1

L2

1
V
FAN
SWITCH

H1
ANTICIPATOR

DEFROST
RELAY

SUP. ELEC.
HT. RELAY

1
Y

AUTO
2

FALL

H1

OUTDOOR
THERMOSTAT

ON

EM. HT. RELAY

4

FAN RELAY

SYSTEM
SWITCH

H2
ANTICIPATOR

FALL

TIME DELAY
FAN RELAY

F
EM. HT. RELAY

6
OFF

H2

E
EM. HT.
LED (RED)

EM. HT.
8
HEAT
FALL

COOL CHANGEOVER
VALVE

AUTO

9

R

CO

COOL

C1 ANTICIPATOR

COMPRESSOR
CONTACTOR
10

1

RISE

C1

INTERNAL
THERMOSTAT

M

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

HIGH
PRESSURE
SWITCH

OVERLOAD

M8375

Fig. 145. Schematic and hookup of T874G with Q674F. Used in heat pump applications.
THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

W1

1

EHR

EHR

REVERSING
RELAY

H1
LPCO

FALL
Y1
H1 ANTICIPATOR

RVR
3

DFR 2

4
H2
ANTICIPATOR
H2

COMPRESSOR
CONTACTOR 1

RVR

FAN
SWITCH

FAN RELAY

AUTO
G
ON

6

L1
(HOT)
L2
1

R

FALL

ODT 3
HEAT
RELAY 2

8
W2

C1
SYSTEM
SWITCH
RISE

ODT 2

OFF

HEAT RELAY 3

SUPL. HT.

9
C1
ANTICIPATOR

E

HEAT
10

X

AUTO
SUPL.
HEAT
LED
(RED)

COOL
C2
ANTICIPATOR

RISE
C2

HEAT RELAY 1

EHT

11

SUPL. HT.
RELAY

C
DFR 2

COMPRESSOR
CONTACTOR 2

Y2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

Fig. 146. Schematic and hookup of T874D with Q674F. Used in heat pump applications.

60-2485—8

158

M7010

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
A

2

H1

H1
ANTICIPATOR

MODE SIGNAL

1
3

FALL
3

FAN
SWITCH

2

4

AUTO

G
FAN RELAY

ON

5

L1
(HOT)
L2
1

R

H2
ANTICIPATOR

2

S

SERVICE
LED (RED)

6

W3

FALL H2

HEAT RELAY 2

HEAT RELAY 1
SYSTEM
SWITCH

W2

AUX. HT.
LED (GRN)

OFF

X

8
COOL

CO

EM. HT.
LED (YEL)

AUTO

COOL
CHANGEOVER
VALVE

O

9

RISE

L

COMPRESSOR
CONTACTOR

HEAT
EM. HT.

Y
EM. HT. RELAY

C1
ANTICIPATOR

RISE

E
10

C1

T
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

CONNECT TO Y OR W TERMINAL WITH FACTORY INSTALLED JUMPER.

3

MODE SIGNAL

JUMPER FACTORY INSTALLED.

M7024

Fig. 147. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

H1 ANTICIPATOR
O

1

COOL CHANGEOVER
VALVE
DEFROST
RELAY

2

BLOWER SPEED
RELAY

FAN
SWITCH
BLOWER RELAY
AUTO
G

FALL

H1

ON
L1
(HOT)

R

L2

4

1

6
SYSTEM
SWITCH

FALL
H2 ANTICIPATOR

OFF

H2
8

CO

RISE

9

EM. HT.

DEFROST
AUX. HT. RELAY
RELAY
EM. HT.
LED
(RED)

W2
EM. HT. RELAY

HEAT

E

AUTO

C
LOCKOUT
THERMOSTAT

COOL
C1
ANTICIPATOR
C1

RISE

COOL
CONTRACTOR

Y
10
M8382

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 148. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

159

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
2R

EMR4
FALL

W1

1

H1

1R
Y1

H1 ANTICIPATOR

4R2

2R2
5R

4
FALL

G
EMR4

H2

H2
ANTICIPATOR

6

3R

W2
EMR2
THERMAL SWITCHES
FOR HEATING
ELEMENTS
HTR 1

8

RISE

FAN
SWITCH
C1

HTR 3

AUTO

HTR 2

EMR3

ON
9
C1
ANTICIPATOR

RISE
3
C2

10

2
EM. HT. LED

C2
ANTICIPATOR

X1

11

SYSTEM
SWITCH

3R1
Z

OFF
1 POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
2 OPTIONAL FIELD WIRE JUMPER TO ALLOW
SINGLE SYSTEM TRANSFORMER.
3 FOR Q674F1048, DELETE C2 STAGE.

OUTDOOR
THERMOSTAT

RC

EM. HT.

EMR1
EMR1

HEAT
RH
AUTO
COOL

EM. HT. RELAY
E

L1
(HOT) L2

1

L1 L2
(HOT)

1
M8380

Fig. 149. Schematic and hookup of T874C with Q674F. Used in heat pump applications.

60-2485—8

160

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER VALVE

H1 ANTICIPATOR
1

R
COMPRESSOR
CONTACTOR

FALL

INTERNAL
THERMOSTAT

M

2
H1

OVERLOAD
SWITCH

FAN SWITCH
AUTO

3

F

HI PRESSURE
SWITCH

FAN
RELAY

ON
OUTDOOR
THERMOSTAT
FALL

5

SUPL. ELEC.
HT. RELAY

Y

H2
EM. HT. RELAY
CONTACT

H2 ANTICIPATOR

TIME DELAY
FAN RELAY

6
SYSTEM
SWITCH

RISE

8

TIME DELAY
FAN RELAY
E

OFF

EM. HEAT
LED (RED)

EM. HT.

C1

X

HEAT
RISE

CO

9

SYSTEM
MONITOR

COOL

1
L1
HOT
L2

AUTO

C1
ANTICIPATOR

VR
2

10

L2

V
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2 REMOVE FACTORY INSTALLED V-VR JUMPER WHEN CONNECTING
A TWO TRANSFORMER SYSTEM.

1

L1
HOT
M2852A

Fig. 150. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

161

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
EM. HT. RELAY
CONTACT 1

L2
L1
(HOT)

H1
ANTICIPATOR
1

R

1

W2

2

FAN
SWITCH
AUTO

FALL
H1

T6031 REFRIGERATON/
TEMPERATURE
CONTROLLER

EM. HT.
LED
(RED)

ON

EM. HT.

E

4
2
6
SYSTEM
SWITCH

H2
ANTICIPATOR

EM. HT. RELAY

X
H

OFF
FALL

H2

Y

EM. HT.
HEAT

R8233B

Y

COMPRESSOR
CONTACTOR

R
COM

AUTO
G

8

G

EM.
HT.

COOL
CO
W
RISE
9

O

SEQUENTIAL
RELAY

O
FAN

C1
ANTICIPATOR

C

DF

RS

10

C1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

OPTIONAL FIELD WIRE JUMPER TO CYCLE W2 WITH H1 IN EM. HT.
(FASTER RESPONSE).

RISE

1
L1
(HOT)

L2

REVERSING
SOLENOID

Fig. 151. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

60-2485—8

162

FAN
M4710

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
1

L1 L2
(HOT)

HEAT RELAY
W1
COMPRESSOR
CONTRACTOR 1

1
FALL
H1

Y1
FAN SWITCH

H1 ANTICIPATOR

FAN RELAY

AUTO
G
ON

4

RC
3

FALL
H2 ANTICIPATOR

H2

HEAT RELAY 2

W2

6
SYSTEM
SWITCH

RISE

RH
EM. HT. RELAY

OFF
8

E
EM. HT.

C1

HEAT

9

B
AUTO

10
RISE

C1 ANTICIPATOR

2
X2

COOL
EM. HEAT
LED (RED)

11
C2

X1

C2 ANTICIPATOR
COMPRESSOR
CONTRACTOR 2

O
Y2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FACTORY SUPPLIED FIELD INSTALLED JUMPER TO E-X2 FOR CONSTANT POWER TO EM HT LIGHT IN EM HT POSITION.

3

1
L1 L2
(HOT)

OPTIONAL FIELDWARE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

M8377

Fig. 152. Schematic and hookup of T874D with Q674F. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
COOL CHANGEOVER
VALVE

1

O

H1
ANTICIPATOR

FAN RELAY
AUTO
G
2

H1

ON

L1
(HOT)
L2
1

FAN
SWITCH

FALL
4

R

6

W2
SYSTEM
SWITCH

FALL

OUTDOOR
THERMOSTAT

AUX. HT. RELAY

H2 ANTICIPATOR
OFF

H2
8
C1

RISE

AUX. HT. RELAY
CONTACT

EM. HT.
RELAY

HEAT
9

CO

E

EM. HT.

RISE

AUTO
COOL

EM. HT. LED
(RED)
X

C1 ANTICIPATOR
Y
10

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

M8381

Fig. 153. Schematic and hookup of T874G with Q674F. Used in heat pump applications.
163

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1

R

1

H1 ANTICIPATOR

2

FAN
SWITCH
AUTO

L2
L1
(HOT)

W2

T6031
REFRIGERATION
TEMPERATURE
CONTROLLER

E
FALL

ON

H1

EM. HT.
LED (RED)

4

EM. HT. RELAY
CONTACT 1

EM. HT.

X
2
H2 ANTICIPATOR
6

SYSTEM
SWITCH
OFF

EM. HT. RELAY

A

COMPRESSOR
CONTACTOR

COMP. FAULT
LED (YELLOW)

H2
EM. HT.

FALL

H

8
HEAT

Y

Y

G

G

R
COM

AUTO
9

SEQUENTIAL
RELAY

R8233B

COOL
W

EH

H1 ANTICIPATOR
RISE

CO

O

O
FAN

10
C

DF

RS
FAN

C1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

2

OPTIONAL FIELD WIRE JUMPER TO CYCLE W2 WITH H1
IN EM. HEAT(FASTER RESPONSE).

RISE

L1
L2
(HOT)
REVERSING
SOLENOID

Fig. 154. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

60-2485—8

164

M2858

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

H1 ANTICIPATOR

R

2

RTD1

L1
(HOT)

OTD1

FAN
SWITCH

L2 1

3
EHR1

AUTO

RTD2

2
FALL

H1

W3

ON
4

ODT2
W2

H2
ANTICIPATOR

EHR2

RTD3

5

H2
FALL

6

AUX. HT.
LED (GRN)

SYSTEM
SWITCH

RTD1
X

OFF

SYSTEM
MONITOR

8
COOL
9
RISE

C1
ANTICIPATOR

CHANGEOVER

EM. HT.
LED (RED)

AUTO

FAN
RELAY

L
G

HEAT

RD
COOL
CHANGEOVER VALVE

EM. HT.
10
O

RISE

EM. HT.
RELAY

C1
E
LACO

COMPRESSOR
CONTACTOR

CHP

Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

W3 TERMINAL ON SELECT MODELS.

M1589

Fig. 155. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

165

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
L2
(HOT)
1
COOL
CHANGEOVER VALVE

H1
ANTICIPATOR

FALL

O

1
FAN
SWITCH
ON

H1

FAN RELAY

2

G
ON
R

4

FALL

AUX. HT.
RELAY
CONTACT

OUTDOOR
THERMOSTAT

EM. HT.
RELAY

E

H2 H2 ANTICIPATOR

6

RISE

8

SYSTEM
SWITCH
OFF

L1

CO
9

HEAT
X

AUTO
C1 ANTICIPATOR

EM. HT. LED
(GREEN)

COOL

10

RISE

COMPRESSOR
FAILURE

EM. HT. LED
(RED)

EM. HT.

AUX. HT. RELAY

W2
COMPRESSOR CONTACTOR

C1
1

Y

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M5720

Fig. 156. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
COOL CHANGEOVER
VALVE

1

Y1

L1
(HOT)

FAN SWITCH

FALL

2
H1

L2

FAN RELAY

AUTO
G

H1 ANTICIPATOR
ON
3

R

4

CHECK LED
(GREEN)

DEFROST
RELAY

TIME DELAY
RELAY 2

X
H2 ANTICIPATOR
FALL

6
W2
H2

SYSTEM
SWITCH
8

RISE
9
C1 ANTICIPATOR
10

E

OFF

EM. HT.
LED (RED)

EM. HT.

C1

CO

TIME DELAY
RELAY 1

LOCKOUT
RELAY

HEAT
AUTO

HI PRESSURE
SWITCH

COOL

COMPRESSOR
CONTACTOR

W1
C1
RISE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 157. Schematic and hookup of T874G with Q674F. Used in heat pump applications.
60-2485—8

166

M2860

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT) L2
1

1

O

H1 ANTICIPATOR

COOL CHANGEOVER VALVE
2

H1

E

FAN
SWITCH

EM. HT. RELAY

AUTO
G

FALL
ON

2
4

FAN RELAY

B
R

HEAT CHANGEOVER VALVE

H2
W2

6
H2 ANTICIPATOR

FALL

SYSTEM
SWITCH
OFF

AUX. HT. RELAY

L1
8

EM. HT.

AUTO

C1 ANTICIPATOR
9
C1

1

RISE

COMPRESSOR
FAILURE

EM. HT. LED
(RED)

HEAT

CO
RISE

X

COOL

AUX. HT. LED (GREEN)
Y

10

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR CONTACTOR
2

B TERMINAL ON SELECT MODELS.

M5721

Fig. 158. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

167

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER VALVE
O

1
H1 ANTICIPATOR

L1
L2
(HOT)
1
FAN RELAY

G

FAN SWITCH

HEAT RELAY
CONTACT

AUTO
2

OFF
R

H1 FALL

AUX. HT. RELAY
4

6
FALL
H2

W
OUTDOOR
THERMOSTAT

SYSTEM
SWITCH

E
HEAT RELAY
CONTACT

H2 ANTICIPATOR

EM. HT.
RELAY

8
EM.HT.
RISE

9
CO

EM. HT. LED
(RED)

AUTO

X

OFF

COMPRESSOR
CONTACTOR

LIMIT

C1 ANTICIPATOR
Y
10

RISE
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

C1

M5722

Fig. 159. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

THERMOSTAT

SUBBASE

O

FALL
2
H1

SYSTEM COMPONENTS

COOL CHANGEOVER VALVE

FAN
SWITCH

H1 ANTICIPATOR
AUTO

3

G
FAN RELAY

ON
R

4

L2

H2 ANTICIPATOR
FALL

L1
(HOT)

5

1

W
AUX. HT. RELAY

H2
6
RISE
SYSTEM
SWITCH
CO

X
EM. HT. RELAY

8
EM. HT.

EM. HT.
LED (RED)

AUTO
B

9

COMPRESSOR
CONTACTOR

OFF
C1 ANTICIPATOR
RISE

Y
10
C1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 160. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

60-2485—8

168

M5723

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER VALVE

1
L1
(HOT)
L2

O

1
H1 ANTICIPATOR
FAN
SWITCH
AUTO

G

ON

2

FAN RELAY

R

H1
OUTDOOR
THERMOSTAT

FALL
W2

4

EM. HT. RELAY 1
H2

6

EM. HT. RELAY EM. HT. RELAY 2
CONTACT 1

H2 ANTICIPATOR
FALL
SYSTEM
SWITCH

E
2

8

EM. HT. RELAY
CONTACT 2

EM.HT.
RELAY 3

CO
L

C1 ANTICIPATOR
SUPL. HT.

RISE
9

SUPL. HT.
LED (RED)

ON

C
COMPRESSOR
CONTACTOR 1

OFF
C1
RISE

Y

10
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2

N.O. SWITCH — INSTALLER ADDED, TO LIGHT EM. HT. LED
WHEN COMPRESSOR OPERATION IS NOT NORMAL.

M5724

Fig. 161. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

169

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THEROMSTAT

SUBBASE

SYSTEM COMPONENTS
C815A OUTDOOR
THERMISTOR
T

1
FAN RELAY

FALL
FAN SWITCH

G

H1
2

AUTO

COOL
CHANGEOVER VALVE

ON

H1 ANTICIPATOR

O
3
R
1

4

FALL

L1
(HOT)
L2

H2
OUTDOOR
THERMOSTAT

5
X2
AUX. HT. LED
(GREEN)

RESET HEATER
6
SYSTEM SWITCH
RISE

8

EM. HT.
B
AUTO

CO

EM. HT.
LED (RED)

OFF

C1

Y

10
C1
ANTICIPATOR
1

EM. HT. RELAY
F

9

RISE

AUX. HT. RELAY
W

COMPRESSOR
CONTACTOR
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 162. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

60-2485—8

170

M5725

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L2
L1
(HOT)

HEAT DAMPER

1
B
H1
ANTICIPATOR

HEAT RELAY 1
W1

1
FAN
SWITCH

FAN RELAY
H1

AUTO

FALL

4

G

ON

H2
ANTICIPATOR

HEAT RELAY 2
6

1

AUTO
8

H2

FALL

SYSTEM
SWITCH

9

W2

R

OFF
RESET

S1

1

CO

RESET CIRCUIT
COOL
CHANAGEOVER VALVE

O

FALL
10

S2

C1
ANTICIPATOR

RESET CIRCUIT

C1
Y

RISE

SERVICE LED (RED)
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

H2 HAS 10¡F FIXED SETBACK FROM H1 ON T874G1485, 0-12¡F
ADJUSTABLE ON T874G1535.

3

RESET IN MOMENTARY POSITION, SPRING RETURN TO OFF UPON
SWITCH RELEASE.

COMPRESSOR
RELAY

X
ON LED (YELLOW)
A
M1820C

C

Fig. 163. Schematic and hookup of T874G with Q674C. Used in standard applications.

171

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2

1
H1
ANTICIPATOR
2

O
COOL CHANGEOVER
VALVE

FALL

3

Y

FAN SWITCH

H1

COMPRESSOR
CONTACTOR

AUTO
G

4

ON
R

6

FAN RELAY

RISE
2
SYSTEM SWITCH

8

CO

L
MALFUNCTION
LED (RED)

OFF
9
C1
ANTICIPATOR
RISE

AUTO

X

10
C1

HEAT CHANGEOVER
VALVE

B

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2

R-L JUMPER SUPPLIED BY HONEYWELL.

MALFUNCTION
SWITCH
M5726

Fig. 164. Schematic and hookup of T874H with Q674C. Used in standard applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1
(HOT)
L2

1

1

FALL

H1
3

J

2

R1 N.O.2

S1 RELAY

SOLENOID RELAY

S1 N.C.

H1 ANTICIPATOR
3

4

S
FAN
SWITCH

2

AUTO
G
ON

H2 ANTICIPATOR

R
5

C
H2

H2
FALL

FAN RELAY

AUX. HT. RELAY

7

R1 N.C.1
8

SYSTEM
SWITCH

COMPRESSOR
CONTACTOR

H1

OFF
R2 N.O. 1

AUTO

REV. VALVE

9
3
C1
RISE
1

C1
ANTICIPATOR
10

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

R1 RELAY
O
2

FIELD REMOVABLE JUMPER.

3

H1 AND C1 ARE DPST SWITCHES.

Fig. 165. Schematic and hookup of T874L with Q674C. Used in heat pump applications.

60-2485—8

172

M5727

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

L1
(HOT)
1
L2

FALL
FAN
SWITCH

H1
1
H1 ANTICIPATOR

AUTO

W1

ON

HEAT RELAY 1

AUX. HT. LED
(GREEN)

4

EM. HT. LED
(RED)

X
W2

FALL

6
HEAT RELAY 2

H2
RH
SYSTEM
SWITCH

H2 ANTICIPATOR

L
8

OFF
SYSTEM
MONITOR

EM. HT.

RISE

HEAT

C1
9

EM. HT. RELAY

E

AUTO

G
FAN RELAY

COOL
10

RC
COMRESSOR CONTACTOR 1

C1 ANTICIPATOR
Y1
C2 ANTICIPATOR

COMRESSOR CONTACTOR 2
11

Y2

RISE
C2

L2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
M5728

1
L1
(HOT)

Fig. 166. Schematic and hookup of T874D with Q674F. Used in standard applications.

173

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L2

(HOT) L1

1

R
ODT 1

H1 ANTICIPATOR
2

FALL

RTD 1
H1
3

4

RTD 2

FAN SWITCH
ODT 2
AUTO
EHR 2

ON

H2
ANTICIPATOR
5

H2

EHR 1

RTD 3

W2

RTD 1

AUX. HT.
LED (GREEN)

FALL

X

SYSTEM
SWITCH

EM. HT.
LED (RED)

COMPRESSOR
FAILURE

RD

OFF
L
7
FALL
CHANGEOVER
8

EM. HT.
HEAT

G

AUTO

B

FAN RELAY
HEAT
CHANGEOVER
VALVE

COOL

9

EM. HT.
RELAY

E
C1
ANTICIPATOR

10

EHT1
CHP

LACO
Y
COMPRESSOR
CONTACTOR

C1
RISE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 167. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

60-2485—8

174

M1592A

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

W3

W3 RELAY

O
COOL CHANGEOVER
VALVE
L
H1
ANTICIPATOR
1

FAN
SWITCH

COMPRESSOR
MONITOR
FAN RELAY

G

AUTO
ON

C ANTICIPATOR

L1
(HOT)
L2

R

2

1
W2

H1
C

4

5
H2
ANTICIPATOR
H2

EM. HT.
LED (RED)

3

FALL

SYSTEM
SWITCH

E
EM. HT. RELAY

EM. HT.
HEAT

6

AUX. HT.
LED (GRN)

AUX. HT. RELAY

OFF

FALL
COOL

X
3
X2

HEAT
CHANGEOVER
VALVE

B
11

W1 RELAY

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

W1

2 REMOVE JUMPER WHEN W1 RELAY IS USED.

2

3 FACTORY-INSTALLED JUMPER.

COMPRESSOR
RELAY

Y

M5067

Fig. 168. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

175

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

1
FALL

H1 ANTICIPATOR

SYSTEM COMPONENTS

O
FAN SWITCH

COOL CHANGEOVER
VALVE

AUTO

2

G
ON

FAN RELAY

H1

B
3

B RELAY

W3

4

AUX HT. RELAY
SYSTEM
SWITCH

H2
ANTICIPATOR

L2
E

OFF

HEAT

EM. HT. RELAY

EM. HT.
LED (RED)

AUTO
X

2

COOL

8
C1

1

L

EM. HT.

H2 FALL

RISE

AUX. HT.
LED (GREEN)
AUX. HT. RELAY

9

W2
C1 ANTICIPATOR

Y
10

CO

11

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

12

2

TERMINAL LABELED C/X ON SOME MODELS.

3

W3 TERMINAL ON SOME MODELS ONLY.

RISE

COMPRESSOR
CONTACTOR

M5986A

Fig. 169. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

60-2485—8

L1
(HOT)

R

6

176

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

W3
W1 RELAY
W3 RELAY
W1
2

H1
FALL

H1 ANTICIPATOR

B RELAY
FAN SWITCH
B

3

FAN RELAY
AUTO
G

4

L1
(HOT)

ON
R

5

AUX. HT. RELAY
6
H2
ANTICIPATOR

SYSTEM
SWITCH

AUX. HT.
LED (GREEN)

OFF
EM. HT.

H2

X

3
HEAT

8

FALL

9
CO
C1 ANTICIPATOR

L2
1

W2

EM. HT.
LED (RED)

AUTO
COOL

L
E

RISE
10
RISE

O
C1
2
1

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

ON SOME MODELS, Y TERMINAL MAY BE LABELED Y1.

3

EMERGENCY HEAT RUNS CONTINUOUSLY WHEN SWITCH IN IN EM. HT. POSITION.

COMPRESSOR
FAULT
COOL
CHANGEOVER
VALVE

EM. HT.
RELAY
COMPRESSOR
CONTACTOR

Y

M5987A

Fig. 170. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

177

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1
(HOT)
L2

R
2

1

FALL
H1

Y

FAN
SWITCH

3
H1 ANTICIPATOR

O.D.T.

COMPRESSOR
CONTACTOR

AUTO
G

4

ON

FAN RELAY

H2 ANTICIPATOR

EM. HT. LED
(RED)

FALL

H2

HCR1

W1

5

HCR1

6

F

8

C

9

E

HCR2

2
CO

SYSTEM
SWITCH

RISE
C1 ANTICIPATOR

HCR2
X

EM. HT.
10

"X" RELAY

AUTO

"P" RELAY

OFF
P

11
C1

RISE

CO

HCR3

O
12

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

EXTERNAL JUMPER SUPPLIED BY HONEYWELL.

COOL CHANGEOVER
VALVE
M5729

Fig. 171. Schematic and hookup of T874J with Q674J. Used in heat pump applications.

THERMOSTAT

SUBBASE

2
H1 ANTICIPATOR

SYSTEM COMPONENTS

FAN
SWITCH
FAN RELAY
AUTO
G

3
ON

R

4

O

FALL
FAULT
LED
(RED)

H1

RISE

SYSTEM
SWITCH

CO

COOL
CHANGEOVER
VALVE

C

8
C1 ANTICIPATOR

2

CHECK
FILTER
3
LED (YELLOW)

9
HEAT
10

L1
(HOT)
L2
1

OFF
COOL

11

12

Y

C1
RISE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

Fig. 172. Schematic and hookup of T874H with Q674B. Used in heat pump applications.

60-2485—8

178

M1401

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

FAN
SWITCH

2

FAN RELAY

H1 ANTICIPATOR

AUTO
G

3
ON

R

4

O

FALL
FAULT
LED
(RED)

H1

C

8

RISE

COOL
CHANGEOVER
VALVE

2

C1 ANTICIPATOR

SYSTEM
SWITCH

CO

CHECK
FILTER
3
LED (YELLOW)

9
OFF
10

L1
(HOT)
L2
1

AUTO

11

12

Y

C1
1

RISE

COMPRESSOR
CONTACTOR

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

M1400

Fig. 173. Schematic and hookup of T874H with Q674C. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1
HA
2
FAN
SWITCH
3

FAN RELAY
AUTO
G

H1

ON
EM.. HT. RELAY

FALL
H2

4

X2

5

T

ODA
C815A
OUTDOOR
THERMISTOR

FALL

1
L1
(HOT)
L2

R

6

"F" RELAY
C1

8

F

SYSTEM
SWITCH

AUX. HT. RELAY

EM. HT.
RISE
9

W

AUTO
EM. HT.
LED (RED)

OFF

2

CA
U

10
AUX. HT.
LED (GREEN)

C2

B
COOL CHANGEOVER
VALVE

RISE
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

2

REMOVABLE JUMPER.

O

COMPRESSOR
CONTACTOR

Y

M1403

Fig. 174. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

179

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

H1 ANTICIPATOR
1

O
FAN
SWITCH

2

FAN RELAY

ON

COOL
CHANGEOVER VALVE

G
AUTO

FALL

L1
(HOT)

R

L2 1
4
H2
ANTICIPATOR

H.C.R. 1

O.D.T.
W2

6

H.C.R. 1

H.C.R.2

H.C.R. 2

H.C.R.3

FALL
8

SYSTEM
SWITCH
E

C1 ANTICIPATOR

SUPL. HT.
9

L

ON

CO

RISE

MANUAL
(RED)

AUTO
(YEL)

OFF

C

10

Y
HEAT PUMP
(GRN)

C1

RISE

DEFROST
(RED)

COMPRESSOR
CONTACTOR

D
1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M2112A

Fig. 175. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

THERMOSTAT

SUBBASE

2
FALL

SYSTEM COMPONENTS

Y1
COOL
CHANGEOVER VALVE

H1 ANTICIPATOR

H1
3

Y2
COMPRESSOR
CONTACTOR

4
AUTO

FALL

G
ON

SETBACK

2

FAN RELAY
OPEN-NIGHT
CLOSED-DAY

FAN SWITCH
6
SYSTEM
SWITCH

RISE
8

L2
1
L1
(HOT)

R
SETBACK RELAY

OFF
L

CO
9

AUTO
X1

LED

10

C

3
RISE

LED

C1 ANTICIPATOR

X2

C1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

SETBACK STAGE OFFSET 12°F (7°C) FROM H1 STAGE.

3

LEDS ON SOME MODELS.

M5730

Fig. 176. Schematic and hookup of T874G with Q674C. Used in standard applications.

60-2485—8

180

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
LOCKOUT
(RESET) RELAY

H1 ANTICIPATOR

FAN
SWITCH

1

X
RESET LED
(RED)

AUTO

G

H1

ON

FALL

FAN RELAY

4

3

L1
(HOT)
L2

R1

6
SYSTEM SWITCH

H2

1

R2

OFF

FALL

AUTO

7

2
B

CO
8

RISE

2

HEAT CHANGEOVER
VALVE

O
COOL
CHANGEOVER VALVE

9
Y

C1 ANTICIPATOR
10

C1

RISE

1

COMPRESSOR
CONTACTOR
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

USE EITHER 'B' OR 'O' ONLY FOR SYSTEM CHANGEOVER. 0.8A AT 30 VAC MAXIMUM LOAD CURRENT.

3

SECOND STAGE HEAT MAKES 12oF (7oC) AFTER FIRST STAGE HEAT TO PROVIDE SETBACK
M114C

Fig. 177. Schematic and hookup of T874G,H with Q674C. Used in standard applications.
THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

FALL

CHANGEOVER RELAY

H1

W1

1
FAN
SWITCH

H1 ANTICIPATOR

AUX.HT. RELAY

3

W2

AUTO
ON

R

4

L1
(HOT) 1
L2

L

6
FALL
H2

H2 ANTICIPATOR

SERVICE
LED (RED)

SYSTEM
SWITCH
OFF
8

X

COOL

EM, HT. LED
(YELLOW)

C0
AUTO
RISE

9
C1 ANTICIPATOR

FAN RELAY

G

HEAT
EM.HT.

COMPRESSOR RELAY

10

C
EM.HT. RELAY
K

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M18623

Fig. 178. Schematic and hookup of T874N with Q674F. Used in heat pump applications.

181

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

W1

1

DEFROST
RELAY
H1
ANTICIPATOR

OUTDOOR
THERMOSTAT

REVERSING
VALVE
HEAT
RELAY 2

EM.HT. RELAY
CONTACT
2

EM.HT. RELAY
CONTACT

HEAT
RELAY 3

H1
W3

FALL
4

FAN SWITCH
FAN RELAY

H2
ANTICIPATOR

AUTO
G
ON

5

1

L1
(HOT)
L2

R

H2
FALL
6

W2

SYSTEM
SWITCH
OFF

EM. HT.
LED (RED)

EM. HT.
RELAY
X

EM. HT.

CHECK
LED
(GREEN)

8
HEAT

OPTIONAL
COMPRESSOR
FAILURE DEVICE

L

RISE
9
C1
ANTICIPATOR

C1

AUTO
HIGH
PRESSURE
SWITCH

COOL

CO

COMPRESSOR
CONTACTOR

Y

10
1

HEAT
RELAY 1

E

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 179. Schematic and hookup of T874N with Q674F. Used in heat pump applications.

60-2485—8

182

M3686

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
FAN DELAY
RELAY

1

CHANGEOVER VALVE

ELEC. HT.
RELAY STG. 1

L2

R-11

R-11
FALL

1

W1

H1

R-10

H1
ANTICIPATOR

R-8

R-6

OVERLOAD

Y1
FAN
SWITCH
FAN RELAY

AUTO
G
ON

R-6
R-1

R-2

4
FALL

R

H1
H2
ANTICIPATOR

COMPRESSOR
CONTACTOR

R-10
6

W2

8

EM. HT.
LED
(RED)

ELEC. HT. RELAY
STG. 2

E

C1

X2

SYSTEM
SWITCH

RISE

RISE

10

R-5
2

9
C1 ANTICIPATOR

EM. HT.
AUTO

EM. HT. RELAY

R-6

FILTER
LED
(YELLOW)

RANDOM START
R-8 (OPT.)

OFF
11

(HEAT PUMP
OPERATION) R-10

R-5

C2 ANTICIPATOR
C2

T2

Y2

(BIOLERLESS
OPERATION ) R-11

R-3

X1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FILTER LED ON SOME MODELS.

M5957

Fig. 180. Schematic and hookup of T874A,D with Q674J. Used in heat pump applications.

183

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENT
L1

2

TIME
CLOCK

CO
3
H2

L2

(HOT)

FALL

1

Y

FALL

COMPRESSOR
RELAY

FAN
SWITCH

4

AUTO
G
ON
FALL

FAN RELAY

6
H1
ANTICIPATOR

H1

R
W

8
RISE

REVERSING
VALVE

W2
SYSTEM
SWITCH

C1
9
C1
ANTICIPATOR

COMPRESSOR
FAULT LED (RED)

OFF

10

COMPRESSOR
FAULT

A

AUTO

1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M18587

Fig. 181. Schematic and hookup of T874K with Q674C. Used in heat pump applications.

THERMOSTAT

H1/C
ANTICIPATOR

SUBBASE

1

T

2

H1
FALL

SYSTEM COMPONENTS

FAN
SWITCH

H2
ANTICIPATOR
3

W2

AUTO

OUTDOOR
RESET
AUX. HT.

FAN
G

4

ON
R

5
RESET
6

H2
FALL

E

SYSTEM
SWITCH

EM. HT.
W89
HEAT
PUMP
CONTROL
PANEL

B
EM. HT.

EM. HT.
LED (YELLOW)

HEAT

EM. HT. LIGHT
X
SERVICE
LED (RED)

OFF
COOL

L

SERVICE
LIGHT
COOL/HEAT

O
Y

COMPRESSOR
M3951

Fig. 182. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

O

1

H1
ANTICIPATOR

FALL

SYSTEM COMPONENTS

2

H1

COOL CHANGEOVER
VALVE

FAN
SWITCH
AUTO
G
ON

2BH

FAN RELAY

4
R
H2
ANTICIPATOR

O. D. S.

FALL

1BH

SH

6

H2

E
SYSTEM
SWITCH

RISE

L1

8

EM. HT.
LED (RED)

CO
C1
ANTICIPATOR

9

X

EM. HT.

AUX. HT.
LED (GREEN)

ON

10

COMPRESSOR
FAILURE

1BH

W

OFF
RISE

Y

C1

COMPRESSOR
CONTACTOR

1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

L1 L2
(HOT)
M3950

Fig. 183. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

H1
ANTICIPATOR

HEAT RELAY 1
1

FALL
H1

NO
FAN
SWITCH

W1

W2

4
H2
ANTICIPATOR
FALL
H2

1
HEAT RELAY 2

L2

RH

L1
(HOT)

RC

L1
(HOT)

6
SYSTEM
SWITCH

RISE
C1

9
C1
ANTICIPATOR
C2
ANTICIPATOR

OFF

1

COMPRESSOR
CONTACTOR 1

AUTO
10
Y1

Y2

11
RISE
C2

L2
1

8

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 2

M3953

Fig. 184. Schematic and hookup of T874A,F with Q674G. Used in standard applications.

185

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
L2
(HOT)

H1
ANTICIPATOR

HEAT RELAY
1

1

W1

FALL
AUTO

FAN
SWITCH

H1

G
ON

FAN RELAY
RC

W2
4

HEAT RELAY 2

H2
ANTICIPATOR

FALL

SYSTEM
SWITCH

6

H2

RH

IGNITION
RELAY

OFF
RISE
C1

8

HEAT

9

AUTO

C1
ANTICIPATOR
10

B

COMPRESSOR
CONTACTOR 1

COOL

C2
ANTICIPATOR
RISE

Y1

Y2

11

COMPRESSOR
CONTACTOR 2

C2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

1

L1 L2
(HOT)
M3954

Fig. 185. Schematic and hookup of T874D with Q674E. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

FALL
H1
H1
ANTICIPATOR

1

FALL
H2

5

NO
FAN
SWITCH

7

C2

L1
(HOT)

8

W2
SYSTEM
SWITCH
OFF

FAN RELAY
B

AUTO
FAN RELAY

9

O

10

RC

11

Y2

C1
ANTICIPATOR

RISE

L2

RH
HEAT RELAY 2

6

RISE
C1

1
HEAT RELAY 1

4

H2
ANTICIPATOR

W1

C2
ANTICIPATOR

L2
L1
(HOT)
1
COMPRESSOR
CONTACTOR 2

12
Y1
1

COMPRESSOR
CONTACTOR 1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

M3955

Fig. 186. Schematic and hookup of T874D with Q674G. Used in standard applications.

60-2485—8

186

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

R4
FALL
HEAT RELAY 2

H1

R3

2
FAN
SWITCH

H1
ANTICIPATOR

HEAT RELAY 1
R2

HIGH

3

HI SPEED
FAN RELAY

LOW
R1
4

H2
ANTICIPATOR

C

HIGH
TEMP.
SWITCH

HIGH
PRESSURE
SWITCH

LO SPEED
FAN RELAY

LR

COOL
CONTACTOR

LOCKOUT
RELAY

5
R5

FALL
H2
SYSTEM
SWITCH
RISE
C1

8

X

1
L2

HEAT
R

L1
(HOT)

OFF
C1
ANTICIPATOR

COOL
1

10

POWER SUPPLY. PROVIDE DISCONNECT MEANS
M3956
AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 187. Schematic and hookup of T874C with Q674B. Used in standard applications.

THERMOSTAT

FALL

SUBBASE

SYSTEM COMPONENTS

H1
ANTICIPATOR

HEAT RELAY 1
1

W1

H1
1
4
5
FALL

H2
ANTICIPATOR

L2
NO
FAN
SWITCH

6

H2

RH

L1
(HOT)

HEAT RELAY 2
W2
T

7

RISE
C1

8

SYSTEM
SWITCH

9

AUTO

B

O

C1
ANTICIPATOR
10
RISE
C2

FAN RELAY

C2
ANTICIPATOR

L2

RC

11

L1
(HOT)
1

Y2
COMPRESSOR
CONTACTOR 2

12
Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 1

M3958

Fig. 188. Schematic and hookup of T874D with Q674G. Used in standard applications.

187

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

FALL
H1

1

B

W1

4
5

FALL

M839
MOTOR

NO
FAN
SWITCH

ANTICIPATOR
H2

L1

6

W2

Y

RH

R

L2
NO
SYSTEM
SWITCH

RC

8
Y2
9
Y1
10
11

M3960

Fig. 189. Schematic and hookup of T874F with Q674D. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

V
2

1
VR

RESET

OG

H1
ANTICIPATOR
FALL
H1

2

IN STAT
1

M
FAN
SWITCH

L1
(HOT)

COMPRESSOR
CONTACTOR

L2

AUTO
3

HI PR

F

SERVICE
RELAY

ON
4

L1
(HOT)

FAN RELAY

L
5
H2
ANTICIPATOR
SERVICE
LED (RED)

H2
6

FALL

L2
3

O. D. S.

EM. HT.

EM. HT. RELAY

1

ELEC. HT. RELAY

Y
7

RISE

C1

E

SYSTEM
SWITCH
C1
ANTICIPATOR

ELEC. HT. RELAY

EM. HT. LED
(YELLOW)

8
EM. HT.

X
HEAT

10

A

OFF

C815A
OUTDOOR THERMISTOR

COOL
R
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

OPTIONAL REMOVABLE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

3

WIRE JUMPER FOR SERVICE LIGHT.

COOL CHANGEOVER
VALVE

M3978

Fig. 190. Schematic and hookup of T874C with Q674L. Used in heat pump applications.

60-2485—8

188

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

2
FALL
H1

C1

H1/C1
ANTICIPATOR
3

SYSTEM COMPONENTS

FAN
SWITCH

Z

AUTO LO

O

"Z" RELAY

COOL CHANGEOVER VALVE

HI
G

CONT.

L2

FAN RELAY
R

4
H2
ANTICIPATOR

FALL

AUX. HT. RELAY
6

H2

L1
(HOT)
1

W2
C

SYSTEM
SWITCH

W1
HEAT RELAY

HEAT
OFF
COOL

COOL
RELAY
Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M3965

Fig. 191. Schematic and hookup of T874R with Q674B. Used in heat pump applications.

THERMOSTAT

FALL

SUBBASE

SYSTEM COMPONENTS

H1
ANTICIPATOR

HEAT RELAY 1
W1

1

H1

SYSTEM
SWITCH

OFF
4
FALL

H2
ANTICIPATOR

AUTO

HEAT RELAY 2

6

H2

W2
FILTER
LED
(YELLOW)

RISE
C1

8

X

SERVICE
LED (RED)

FAN
SWITCH
AUTO

A

G
ON
9

R

2

O

C1
ANTICIPATOR
10

O

L2
FAN RELAY
L1
(HOT)
MOMENTARY
CIRCUIT

1

COMPRESSOR
CONTACTOR 1
C2
ANTICIPATOR

Y1
Y2

11
RISE
C2

COMPRESSOR
CONTACTOR 2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

2

MOMENTARY POSITION. SPRING RETURN TO "ON" UPON SWITCH RELEASE.

M3959

Fig. 192. Schematic and hookup of T874D with Q674C. Used in standard applications.

189

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

H1
ANTICIPATOR

FAN
SWITCH

1

L1
(HOT)
L2

RH

AUTO
FALL

W1

H1

ON

1
HEAT RELAY 1

4

W2

6

B

HEAT RELAY 2

H2
FALL

H2 ANTICIPATOR
CHANGEOVER
RELAY (HEAT)
O

SYSTEM
SWITCH
8

RISE

G

HEAT

C1

CHANGEOVER
RELAY (COOL)

2

OFF

FAN RELAY

9

AUTO
Y2
COOL

COMPRESSOR
CONTACTOR 2

10
C1 ANTICIPATOR
Y1
C2 ANTICIPATOR
11
RC

C2

RISE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

JUMPER RH, RC FOR SINGLE TRANSFORMER.

1
COMPRESSOR
CONTACTOR 1

L2
L1
(HOT)
M3203B

Fig. 193. Schematic and hookup of T874D with Q674E. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
FALL
H1

H1
ANTICIPATOR

Y1
AUTO

3

G
ON
R

FAN
SWITCH

CHECK
LED
(GREEN)

4
FALL

DR
TDR 2
X

H2
ANTICIPATOR

H2

COOL
FAN RELAY CHANGEOVER VALVE

HBTH

W2

6

TDR 1

SYSTEM
SWITCH

E

OFF
RISE

C

8
EM. HT.

EM. HT.
LED (RED)

CO
C1
ANTICIPATOR

9

10

COMPRESSOR
CONTACTOR

HEAT
W1

AUTO

HPA

COOL

1

RISE
C1

L1 L2
(HOT)
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 194. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

60-2485—8

190

M3977

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2
1

COOL
CHANGEOVER
VALVE
H1 ANTICIPATOR
O

1
H1

FAN SWITCH

FAN RELAY

FALL
2

G

AUTO

"B" RELAY

ON
B
4
R
H2
H2
ANTICIPATOR

FALL

6

SYSTEM
SWITCH

EM. HT.
RELAY

E

OFF
8

L
EM. HT.

CO

RISE

HEAT
9

C1 ANTICIPATOR

AUTO
COOL

EM. HT. LED
(RED)
X
AUX.
HT. LED
(GREEN)

10

W2
AUX. HT. RELAY
Y
COMPRESSOR
CONTACTOR

C1

RISE

1

COMPRESSOR
FAULT

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M2974

Fig. 195. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
COOL
CHANGEOVER
VALVE

H1 ANTICIPATOR
O

1
H1

FAN SWITCH

FALL
2

L1
(HOT)
L2
1

FAN RELAY
G

AUTO
ON

R

H.C.R.1

4
W2

H2
H2
ANTICIPATOR

FALL

O.D.T.

6
E
8

SYSTEM
SWITCH

H.C.R.1

H.C.R.2

H.C.R.2

H.C.R.3

CO

RISE

SUPL. HT.
9

C1 ANTICIPATOR

ON
OFF

L
SUPL. HT.
LED
(RED)

C

10
Y

RISE

C1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

M2975

Fig. 196. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

191

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

G

1

FAN RELAY
W
2
AUTO
H1

AUX. HT.
LED (GREEN)

U

2

AUX. HEATER
RELAY

ON

C1

B
3

FALL

FAN
SWITCH

EM. HT.
LED (RED)

COMPRESSOR
MONITOR

F
1
4

L1
(HOT)
L2

R

H2
5

FALL

SYSTEM
SWITCH
T
EM. HT.

6

HEAT

OUTDOOR
THERMISTOR

X2
OFF
11

OUTDOOR
THERMOSTAT

COOL
O

1

COMPRESSOR
RELAY

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

COOL
CHANGEOVER
VALVE

Y
M2970

2 FIELD REMOVABLE JUMPER.

Fig. 197. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1

STAGE 1 HEAT RELAY
W1

1
H1

FAN
SWITCH

FALL

COMPRESSOR
CONTACTOR

AUTO

H1 ANTICIPATOR
3

Y1
ON
FAN RELAY

4
G
H2
FALL

H2
ANTICIPATOR

6
R
7

RISE

C1

OFF
8

STAGE 2
HEAT RELAY

SYSTEM
SWITCH
W2

HEAT
AUTO

9
COOL
10
C2 ANTICIPATOR
M2976

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 198. Schematic and hookup of T874L with Q674E. Used in standard applications.

60-2485—8

192

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT

L1
(HOT)
L2
1

W3 RELAY
H1 ANTICIPATOR
2

W3

FAN SWITCH

FAN RELAY

H1

AUTO

FALL

G
3

ON
R

4

H2

W2

H2
ANTICIPATOR

FALL

5

AUX. HT. RELAY

SYSTEM
SWITCH

AUX. HT. LED
(GREEN)

EM. HT. RELAY
E

EM. HT.
LED (RED)

OFF

COMPRESSOR
FAULT

8

CO

EM. HT.
RISE

CHECK
LED
(RED)

9

HEAT

10

COOL

AUTO

B

C1 ANTICIPATOR

C1

L
X

HEAT CHANGEOVER
VALVE

11

O

RISE
COOL CHANGEOVER
RELAY

12
Y
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

M2977

Fig. 199. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1
T

1

H1

C1
H2 ANTICIPATOR

OUTDOOR
THERMOSTAT

FAN SWITCH

RISE
2

AUTO

3

ON

OUTDOOR
THERMOSTAT

4

FALL

FAN RELAY
G

5

H2
C1 ANTICIPATOR

6

SYSTEM
SWITCH

SERVICE
LED
(YELLOW)

EM. HT.

COOL

SEQ 1

K
COMPRESSOR
CONTACTOR

EM. HT.
LED (RED)
Y

12

W1
1

SERVICE

Z

OFF

H1 ANTICIPATOR

R
X

HEAT

11

SEQ 2

W2

HEAT CHANGEOVER
VALVE

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
M2978

Fig. 200. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

193

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

C1

1
H2
ANTICIPATOR

RISE

T
OUTDOOR
THERMOSTAT

FAN SWITCH

2

AUTO

3

ON

OUTDOOR
THERMOSTAT
FAN RELAY
G

5

H2

SERVICE
LED
(YELLOW)

C1 ANTICIPATOR
SYSTEM
SWITCH

6

EM. HEAT

11

R
X

HEAT

SERVICE

Z

OFF

K
COMPRESSOR
CONTACTOR

EM. HT.
LED (RED)

COOL
H1 ANTICIPATOR

SEQ 1

Y

12

HEAT CHANGEOVER
VALVE

W1
1

SEQ 2

W2

4

RISE

L1
(HOT)
L2
1

C815A
OUTDOOR
THERMISTOR

RESET

H1

SYSTEM COMPONENTS

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M2979

Fig. 201. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

A2

H1

SERVICE
LED (RED)

FALL

HEAT RELAY 1
W1

1
H1 ANTICIPATOR

L1
(HOT)
L2
1

SERVICE
LED (RED)
4

5

NO
FAN
SWITCH

A1
HEAT RELAY 2

H2
H2
ANTICIPATOR

FALL

6

W2
"T" RELAY

7
T
C1

RISE

8
9

RC
SYSTEM
SWITCH

FAN RELAY B
B

OFF
10
C1 ANTICIPATOR

RISE

RH
AUTO

FAN RELAY O

11

O

12

Y2

C2
C2 ANTICIPATOR

1
L1
(HOT)
L2
COMPRESSOR
CONTACTOR 2

Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED

COMPRESSOR
CONTACTOR 1

Fig. 202. Schematic and hookup of T874D with Q674G. Used in standard applications.

60-2485—8

194

M2980

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

COMPRESSOR
CONTACTOR
Y

CO

L1
(HOT)
L2
1

FAN SWITCH

FALL

FAN RELAY
2
3

AUTO

G

ON
R
HEAT CHANGEOVER
VALVE

4
W

H1
6
H1 ANTICIPATOR

FALL

SYSTEM
SWITCH

COMP.
FAULT
(RED)

8
OFF

C1

RISE

W2

9

COMPRESSOR
FAULT

A

AUTO

10
C1 ANTICIPATOR
1

M2981

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 203. Schematic and hookup of T874L with Q674C. Used in heat pump applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

HEAT RELAY 1
1
H1
FALL

W1

FAN
SWITCH

HEAT RELAY 2

AUTO

H1 ANTICIPATOR

L1
(HOT)
L2
1

W2

ON
R
4

LED
(RED)

H2

X
B

H2
ANTICIPATOR

FALL

6

8

EM. HT. RELAY
SYSTEM
SWITCH
OFF

E
FAN RELAY
G

C1

RISE

EM. HT.
9

COMPRESSOR
CONTACTOR 2

HEAT
AUTO

Y2

10

C2 ANTICIPATOR
C2

COMPRESSOR
CONTACTOR 1

COOL

C1 ANTICIPATOR

RISE

2

Y1
11

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

LED IS NOT LABELED. JUMPER W2 TO X FOR AUXILIARY HEAT INDICATION. JUMPER E TO X FOR
EMERGENCY HEAT INDICATION. CONNECT SYSTEM MONITOR TO X TO IDENTIFY WHEN SYSTEM
NEEDS TO BE CHECKED.

M2982A

Fig. 204. Schematic and hookup of T874D with Q674F. Used in standard applications.

195

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1

COOL CHANGEOVER
VALVE

H1 ANTICIPATOR
2

Y1

H1

COMPRESSOR
CONTACTOR

FALL
3

Y2

FAN SWITCH

FAN RELAY

AUTO
4

G
ON
R

6

L
8
CO

RISE

SYSTEM
SWITCH

LED
(RED)
X1

OFF
9

C

AUTO
C1 ANTICIPATOR

C1

RISE

LED
(RED)
10

2

X2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

LEDS ON SOME MODELS.

M2983

Fig. 205. Schematic and hookup of T874H with Q674C. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

R

2
H1

H1 ANTICIPATOR

FALL

FAN SWITCH

COMPRESSOR
CONTACTOR

L1
(HOT)
L2
1

Y
3

AUTO

4

ON

FAN RELAY
H2
ANTICIPATOR

G
H.C.R.1

5

H2

W2

FALL

6
8
CO

RISE

SYSTEM
SWITCH

SUPL. HT.
LED (RED)
L

O.D.T.

SUPL. HT.
9

C1 ANTICIPATOR
10

ON

C

OFF

E

H.C.R.1

H.C.R.2

H.C.R.2

H.C.R.3

11
O
12
RISE
C1

CO

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COOL
CHANGEOVER
VALVE

Fig. 206. Schematic and hookup of T874J with Q674J. Used in heat pump applications.

60-2485—8

196

M2984

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

R

2
H1

FAN SWITCH

H1 ANTICIPATOR

FALL

L1
(HOT)
L2
1

COMPRESSOR
CONTACTOR

Y
3

AUTO

4

ON

FAN RELAY
H2
ANTICIPATOR

G
H.C.R.1

5

H2

W2

FALL

6

CO

RISE

SUPL. HT.
LED (RED)

SYSTEM
SWITCH

8

O.D.T.

L

SUPL. HT.
9

C1 ANTICIPATOR
10

HEAT

C

OFF

E

COOL

H.C.R.1

H.C.R.2

H.C.R.2

H.C.R.3

11
O

12
RISE

1

CO

C1

COOL CHANGEOVER
VALVE

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M2985

Fig. 207. Schematic and hookup of T874J with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
HEAT RELAY 1
W1

1
H1

HEAT RELAY 2

FALL

NO
FAN
SWITCH

H1 ANTICIPATOR

L1
(HOT)
L2
1

W2
RH

4

2

5
H2

RC
H2
ANTICIPATOR

FALL

6
Y2
1

8

COMPRESSOR
CONTACTOR 2

C1

RISE

Y1
9

NO
SYSTEM
SWITCH

L1
(HOT)
L2

COMPRESSOR
CONTACTOR 1

10
C1 ANTICIPATOR
C2 ANTICIPATOR

RISE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

RC-RH REMOVABLE JUMPER WHEN SPECIFIED.

11

M2986

C2

Fig. 208. Schematic and hookup of T874D with Q674D. Used in standard applications.

197

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

R
EM. HT.
RELAY

EM. HT.
LED (RED)

H1

L

C1
FAN SWITCH

H1/C1
ANTICIPATOR

RISE

L1
(HOT)
L2
1

2

AUTO

3

ON

AUX. HT.
LED
(GREEN)

X
AUX. HT. RELAY
W2
FAN RELAY

4
G
6

COOL
CHANGEOVER
VALVE

SYSTEM
SWITCH
H2 ANTICIPATOR
H2

EM. HEAT

O
EM. HT. RELAY

HEAT

FALL

E

OFF

COMPRESSOR
CONTACTOR

COOL
Y

’"B" RELAY
M2987

B

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

1

Fig. 209. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

FAN RELAY
H1
1

FALL
H1 ANTICIPATOR

2
3
HCO

G
FAN
SWITCH
AUTO

R

ON

HEAT
CHANGEOVER
VALVE

FALL
4
H2
H2
ANTICIPATOR

6

8

SYSTEM
SWITCH
OFF

FILTER
B
LED
(YELLOW)
F

HEAT
AUTO

C1

RISE

COOL
CHANGEOVER
VALVE

O

CCO

FALL

L1
(HOT)
L2
1

COOL

L
RESET
LED
(RED)

COMPRESSOR
CONTACTOR 1

9
Y1
10
C1 ANTICIPATOR
C2 ANTICIPATOR

RISE

C2

1

COMPRESSOR
CONTACTOR 2
11

Y2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 210. Schematic and hookup of T874Y with Q674E. Used in heat pump applications.

60-2485—8

198

M2988

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1

W1 RELAY
H1 ANTICIPATOR
2

W1

FAN SWITCH

H1
FALL

FAN RELAY

AUTO
G

3

ON
R
AUX. HT. RELAY
SYSTEM
SWITCH

4

W2
AUX. HT.
LED
(GREEN)

OFF

H2
H2
ANTICIPATOR

FALL

6
EM. HT.

X

HEAT

8

EM. HT.
LED (RED)

AUTO
RISE

C1
ANTICIPATOR

C1

L
COMPRESSOR
FAULT

COOL
10
Y1

1

COMPRESSOR
CONTACTOR

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M2989

Fig. 211. Schematic and hookup of T874G with Q674F. Used in standard applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
HEAT RELAY 1

L1
(HOT)
L2

HEAT RELAY 2

1

W1

1
H1

FAN
SWITCH

FALL

AUTO

H1 ANTICIPATOR

ON

W2
RH

4

2

H2

RC
H2
ANTICIPATOR

FALL

6

FAN RELAY
SYSTEM
SWITCH

8

OFF

C1

RISE

G
Y2
COMPRESSOR
CONTACTOR 2

HEAT

9

AUTO
COOL
10

Y1

1
COMPRESSOR
CONTACTOR 1

L1
(HOT)
L2

C1 ANTICIPATOR
C2 ANTICIPATOR

RISE

C2

11

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

RC -RH REMOVABLE JUMPER WHEN SPECIFIED.

M2990

Fig. 212. Schematic and hookup of T874A with Q674E. Used in standard applications.

199

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SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1

1
2
H1

H1 ANTICIPATOR

FALL

SYSTEM
SWITCH

RELAY 1
N.O. 2

OFF

H1

3
AUTO

COMPRESSOR
CONTACTOR

4
H2

R

FALL

C

7
8

FAN
SWITCH

FIELD
REMOVABLE
JUMPER

AUX. HT. RELAY
H2

LO

CO
9
10
C1 ANTICIPATOR

S1
RELAY N.C.

Y

5
H2 ANTICIPATOR

RISE

S1
RELAY

MED

L
CHECK
LED (RED)

R1 RELAY N.C. 1

COMPRESSOR
CONTACTOR

HIGH
ON

R2
RELAY
N.O 1

COOL
CHANGEOVER
VALVE

O
R1 RELAY
K1 RELAY
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

G1
K2 RELAY
G2
M2991

Fig. 213. Schematic and hookup of T874L with Q674C. Used in heat pump applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

H1

SYSTEM COMPONENTS
L1
(HOT)
L2
1

1

FALL
SYSTEM
SWITCH
HEAT

H1 ANTICIPATOR

2

AUX. HT. RELAY
H1

OFF
R

C1 ANTICIPATOR

R1 RELAY

COOL
O
3

4
C1
RISE
5

COOL
CHANGEOVER
VALVE

L

FAN
SWITCH

R2
RELAY
N.O. 1

LO

COMPRESSOR
CONTACTOR

MED
C
HIGH

CHECK
LED (RED)

ON

COMPRESSOR
CONTACTOR

11

S1 RELAY N.C.

Y
12
1

K1 RELAY

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

G1
K2 RELAY
G2
M2992

Fig. 214. Schematic and hookup of T874A with Q674B. Used in standard applications.

201

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)
L2
1

1
2
H1

H1 ANTICIPATOR

FALL

SYSTEM
SWITCH

RELAY 1
N.O. 2

HEAT

S1
RELAY

H1

3
OFF

COMPRESSOR
CONTACTOR

4

S1
RELAY N.C.

COOL
H2

Y

5
H2 ANTICIPATOR

R

FALL

C
7
8

FIELD
REMOVABLE
JUMPER

FAN
SWITCH

AUX. HT. RELAY
H2

LO
RISE

C1
9
10
C1 ANTICIPATOR

L

MED

CHECK
LED (RED)

R1 RELAY N.C. 1

COMPRESSOR
CONTACTOR

HIGH
ON

R2
RELAY
N.O. 1

11

COOL
CHANGEOVER
VALVE

O
R1 RELAY

12
K1 RELAY
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

G1
K2 RELAY
G2
M2993

Fig. 215. Schematic and hookup of T874L with Q674B. Used in heat pump applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
COOL CHANGEOVER
VALVE
O

H1
ANTICIPATOR

H1
FALL

G

FAN
SWITCH

1

FAN RELAY

L2

AUTO

1
L1
(HOT)

ON
2

R
3R

4

SEQ 2

W1

6
FALL

AUX. HT.
LED
(YELLOW)

H2

SEQ 1
2
E

H2 ANTICIPATOR

SYSTEM
SWITCH
X

RISE

EM. HT.
AUTO

CO
9

OFF

5R
C

SYSTEM
LED
(GREEN)

10

RISE

4R

CHECK
LED
(RED)

8

C1

EM. HT.
RELAY

4R

HPS

C1
ANTICIPATOR

4R

Y

1

COMPRESSOR
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. CONTACTOR

2

REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS.

4R
M1629

Fig. 216. Schematic and hookup of T874G with Q674J. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

D. P.

HEAT CHANGEOVER VALVE

W1

1

ODT
H1
EHR

2
FALL

HEAT
CONTACTOR #2

H1 ANTICIPATOR
EHR
W3
4

HEAT
CONTACTOR #3

FAN SWITCH

H2
ANTICIPATOR

1

G

AUTO
5

L2

FAN RELAY

ON
R

L1
(HOT)

HEAT CONTACTOR #1
H2

W2

6

FALL

SYSTEM
SWITCH

X
CHECK LED
(GREEN)

OFF

OPTIONAL
COMPRESSOR FAILURE

8
AUTO

L

C1
RISE

CO
C1 ANTICIPATOR

1

9
Y
COMPRESSOR
CONTACTOR

10

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
M5900

Fig. 217. Schematic and hookup of T874N with Q674C. Used in heat pump applications.

203

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

L1
(HOT)

R

L2

L
2
H1/C1
ANTICIPATOR
3

EM. HT.
LED (RED)
3

FAN
SWITCH

C1
FALL

4

2

ON

X

H2
ANTICIPATOR
H2
FALL

AUX. HT.
RELAY

W3

AUTO

H1

1

AUX. HT.
LED (GRN)

6

AUX. HT.
RELAY

W2
SYSTEM
SWITCH
EM. HT.

FAN RELAY
G

HEAT
COOL CHANGEOVER
VALVE

OFF

O

COOL
E
EM. HT. RELAY
Y
COMPRESSOR
CONTACTOR
B
1

"B" RELAY
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

TERMINAL LABELED C/X ON SOME MODELS.

3

W3 TERMINAL AVAILABLE ON SOME MODELS ONLY.

M3683A

Fig. 218. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
CONTROL MODULE

1

W1

H1

HEAT RELAY 1
2

FALL

W2

H1
ANTICIPATOR

HEAT RELAY 2
W3

SYSTEM
SWITCH
OFF
4
AUTO
5

Y2

6
A

FALL
H2
ANTICIPATOR

3

SERVICE
LED (RED)

7
FAN SWITCH

FAN RELAY
G

H2
AUTO
C1

RISE

8

L1
(HOT)

R

ON

L2

1

2
9

O

MONENTARY
CIRCUIT
COMPRESSOR CONTACTOR 1

10
Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

MOMENTARY POSITION. SPRING RETURN TO "ON" UPON SWITCH RELEASE.

3

H2 OFFSET 12oF FROM H1.

M5901

Fig. 219. Schematic and hookup of T874C with Q674C. Used in standard applications.

205

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

CONTROL MODULE

1

HEAT RELAY #1

SYSTEM
SWITCH

H1
FALL

OFF

2

H1
ANTICIPATOR

W1
HEAT RELAY #2
W2

AUTO

HEAT RELAY #3
4

W3
COMPRESSOR CONTACTOR #2

5
Y2
FALL

H3

SYSTEM MONITOR
H2
ANTICIPATOR

H2

6

A
SERVICE
LED (RED)

FALL

FAN RELAY
G

7

L2
RISE

C1

8

FAN
SWITCH
AUTO
ON

1

MOMENTARY
CIRCUIT

O

9
2

10

COMPRESSOR CONTACTOR #1
Y1

RISE

C2

L1
(HOT)

R

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

MOMENTARY POSITION. SPRING RETURN TO "ON" UPON SWITCH RELEASE.

M5929

Fig. 220. Schematic and hookup of T874W with Q674C. Used in standard applications.

THERMOSTAT

SYSTEM COMPONENTS

SUBBASE

Y1

2
H1 ANTICIPATOR
H1

3

COOL CHANGEOVER
VALVE

FAN SWITCH

1

AUTO

FALL
4

G

L2

FAN RELAY

ON
R

L1
(HOT)

COMPRESSOR
CONTACTOR
Y2
RISE
B
CO

8
O
9
C1 ANTICIPATOR
10

SYSTEM
SWITCH

X
SERVICE
LED (YELLOW)

OFF

X1

AUTO
C1

1

RISE
C
FILTER LED (RED)

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

24 VAC

X2
M5902

Fig. 221. Schematic and hookup of T874H with Q674C. Used in heat pump applications.

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
L1
(HOT)

R
H1 ANTICIPATOR

L2

2

FALL
H1

3

4

SYSTEM
MONITOR
FAN SWITCH

1

L
FAN RELAY

AUTO

G

ON
W
8

MALFUNCTION
LED (RED)

SYSTEM
SWITCH

HEAT RELAY

C

C1
RISE
9

C1
ANTICIPATOR

HIGH SPEED
LED (YELLOW)

OFF
LOW
SPEED
LED
(GREEN)

HEAT
10
AUTO

C2
ANTICIPATOR

C2

11

COMPRESSOR
CONTACTOR 1
Y1

COOL

COMPRESSOR
CONTACTOR 2

RISE
Y2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M5920

Fig. 222. Schematic and hookup of T874B with Q674E. Used in standard applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
FALL

H1

H1
ANTICIPATOR
3
4

H2

L1
(HOT)

R

FAN SWITCH

L2
AUTO

1

ON

L

H2 ANTICIPATOR

FAN RELAY

G

FALL

AUX. HT. RELAY

5
W2
7
E

RISE
C1

AUX. HT.
LED (RED)
8

SYSTEM
SWITCH

9

OFF

MALFUNCTION
LED (RED)

EM.HT. RELAY

C
HIGH SPEED
LED (YELLOW)

EM. HT.

C1
ANTICIPATOR

HEAT
10

C2
RISE

Y1

AUTO

C2
ANTICIPATOR
11

COMPRESSOR
CONTACTOR 2

COOL

CO

Y2
RISE

1

COMPRESSOR
CONTACTOR 1

LOW SPEED
LED (GREEN)

O

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

COOL
CHANGEOVER VALVE
M5923

Fig. 223. Schematic and hookup of T874S with Q674F. Used in heat pump applications.

207

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

CONTROL MODULE
FALL

1
HEAT CHANGEOVER VALVE

H1

B
HEAT RELAY #1

H1
ANTICIPATOR

W1
COMPRESSOR CONTACTOR #1
4

Y1
FAN
SWITCH
AUTO

FAN RELAY
G

H2
ANTICIPATOR

ON
L1
(HOT)
L2
1

RC

H2

6
FALL
HEAT RELAY #2
W2
8

SYSTEM
SWITCH

RH

OFF
C1

SERVICE
LED (RED)

RISE
9

HEAT

L1
(HOT)
L2
1
SYSTEM MONITOR

A

AUTO
10
COOL

COMPRESSOR CONTACTOR #2
Y2

11
C2

COOL CHANGEOVER VALVE

RISE
O

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 224. Schematic and hookup of T874A,D with Q674E. Used in standard applications.

60-2485—8

208

M5927

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
CONTROL MODULE
HEAT RELAY #1

FALL

1

W1
HEAT RELAY #2

H1
W2
FAN
SWITCH

H1
ANTICIPATOR

HEAT DAMPER
B

AUTO
4
ON

L1
(HOT)

RH

L2
H2
ANTICIPATOR

6

1

L2

1
L1
(HOT)

RC

H2

COOL DAMPER
FALL

O
8

SYSTEM
SWITCH

FAN RELAY
G

C1

RISE
9

COMPRESSOR CONTACTOR #2

OFF
Y2

AUTO
10

COMPRESSOR CONTACTOR #1

11
Y1
C2

1

SERVICE
LED (RED)

RISE

SYSTEM MONTIOR
A

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
M5928

Fig. 225. Schematic and hookup of T874D with Q674C. Used in standard applications.

209

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
CONTROL MODULE
SYSTEM MONITOR
A2

FALL

SERVICE
LED (RED)

H1

NO FAN
SWITCH

H1
ANTICIPATOR

HEAT RELAY #1
W1

1
SERVICE
LED (RED)

SYSTEM MONITOR
A1
HEAT RELAY #2

4

W2
T RELAY

5
T
6
H2

L1
(HOT) 1
L2

RC
H2
FALL ANTICIPATOR

SYSTEM
SWITCH

FAN RELAY B
B

7
OFF
8

L2
L1
1
(HOT)

AUTO
RH

C1

RISE

FAN RELAY O
9

O
COMPRESSOR CONTACTOR #2

10
Y2
11

COMPRESSOR CONTACTOR #1

C2
RISE
1

12

Y1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 226. Schematic and hookup of T874G with Q674G. Used in standard applications.

60-2485—8

210

M5930

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

1
CO
(HEAT)

FAN
SWITCH

W3 RELAY
W3

AUTO
2

FALL

SYSTEM COMPONENTS

H1
ANTICIPATOR

FAN RELAY

G

ON

3

R
AUX. HT.
RELAY

4

FALL

1
L2
L1
(HOT)

W2
H2

EM. HT.
RELAY

5
E

H2 ANTICIPATOR
AUX.
HT. LED
(GREEN)

H1
FALL
6

CO
(COOL)

SYSTEM
SWITCH

8

OFF

9

EM. HT.

RISE

COMPRESSOR
FAULT
X1
CHECK
LED (RED)
X2

HEAT

EM. HT.
LED (RED)

AUTO
10
C1
ANTICIPATOR

X

COOL

COOL CHANGEOVER
RELAY
O

C1
RISE

B
11
W1 RELAY

HEAT CHANGEOVER
RELAY

W1
2

COMPRESSOR
CONTACTOR

Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

W1 - Y1 JUMPER IS Y TERMINAL; REMOVE JUMPER WHEN W1 RELAY IS USED.

M1230B

Fig. 227. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

211

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
L2
(HOT)
1

R

1
H1

FAN
SWITCH

C1 FALL

Y1

2

COMP. RELAY

AUTO

O.L.

IN. STAT.

HI. PRO.

G

H1/C1 ANTICIPATOR
ON

3

FAN RELAY
L
SENSOR
LED (RED)

4
H2 ANTICIPATOR

SERVICE
2

5

EM. HT.
H2

EM. HT. RELAY

O.D.S.
W1

FALL

SYSTEM
SWITCH

6
EM. HT.

E
AUX. HT.
LED
(GREEN)

ELECTRIC
HEAT RELAY
ELECTRIC
HEAT RELAY

EM. HT.
LED (YELLOW)
C

HEAT

C815A OUTDOOR
THERMISTOR

OFF
COOL

T

11
RESET

O
12

COOL CHANGEOVER
VALVE

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

REMOVABLE JUMPER (INSTALLED).

M3259

Fig. 228. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
L1
(HOT)
L2

R
1
FAN
SWITCH

H1 ANTICIPATOR
2

COMP. RELAY

IN. STAT.

O.L.

1

HI. PRO

Y1
AUTO

H2 ANTICIPATOR

ON

3

G
FAN RELAY

H1

SERVICE
LED (RED)

4

FALL

L
SERVICE

5
FALL

H2

O.D.S.

2
6
SYSTEM
SWITCH
OFF

8

RISE

EM. HT. RELAY

W1

RESET

CO

AUX. HT.
LED
(GREEN)

EM. HT.

9
C1 ANTICIPATOR

ELECTRIC
HT. RELAY

EM. HT.
E
EM. HT.
LED (YELLOW)

ELECTRIC
HT. RELAY

HEAT
C

10

COOL

RISE

C815A OUTDOOR
THERMISTOR
T

AUTO

C1

11
O

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

REMOVABLE JUMPER (INSTALLED).

COOL CHANGEOVER
VALVE

M3264

Fig. 229. Schematic and hookup of T874G with Q674F. Used in heat pump applications.
SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

W3 RELAY
W3

O
COOL
CHANGEOVER VALVE

H1
ANTICIPATOR

L
CHECK
LED (RED)

1
C ANTICIPATOR

COMPRESSOR
MONITOR
FAN RELAY

FAN
SWITCH

2
G

AUTO
ON

1

R

L1
(HOT)
L2

H1

C
W2

FALL
3
SYSTEM
SWITCH

EM. HT.
LED
(RED)

EM .HT.

AUX. HT.
LED
(GREEN)

4

AUX. HT. RELAY

E

5
H2
ANTICIPATOR
H2

HEAT

EM. HT. RELAY
X

OFF
6

B

COOL

FALL

HEAT
CHANGEOVER VALVE

Y
11
1

COMPRESSOR
RELAY

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

M5068

Fig. 230. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

213

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
H1

O

H1
ANTICIPATOR

FALL

3

COOL
CHANGEOVER
VALVE

L

FAN
SWITCH

COMPRESSOR
FAULT

EM. HT.
LED (RED)

AUTO
4
ON

1

H2 ANTICIPATOR

SYSTEM
SWITCH

8

E
X
AUX. HT.
LED (GREEN)

OFF
EM. HT.

9

HEAT
10

2

AUTO

W3 RELAY
11

W3
COMPRESSOR
RELAY

12

RISE

HEAT CHANGEOVER
VALVE

B

COOL
RISE

CO

AUX. HT. RELAY

W2

C1
ANTICIPATOR

H1

L2

EM. HT. RELAY

FALL

C1

L1
(HOT)

R

5
H2

FAN RELAY

G

Y

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

ONLY TERMINAL B OR O TO BE USED. 0.8A MAX.

M5152

Fig. 231. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

THERMOSTAT

FALL

SUBBASE

SYSTEM COMPONENTS

H1
ANTICIPATOR

HEAT RELAY 1
1

W1

H1

1
4

NO FAN
SWITCH

L2
RH

L1
(HOT)

5
FALL

H2
ANTICIPATOR

HEAT RELAY 2
6

H2

W2
T

7

8

RISE
C1

9

SYSTEM
SWITCH
OFF
AUTO

O

C1
ANTICIPATOR

RISE
C2

C2
ANTICIPATOR

FAN RELAY
B

10

RC

11

Y2

L2
L1
(HOT)
1
COMPRESSOR
CONTACTOR 2

12
Y1
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR 1

M3957

Fig. 232. Schematic and hookup of T874D with Q674G. Used in standard applications.

60-2485—8

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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

FALL
H1

SUBBASE

H1
ANTICIPATOR

SYSTEM COMPONENTS

1
COMPRESSOR
HIGH SPEED

Y1
H2
ANTICIPATOR

2

3
FALL

AUTO

FAN

G

4

ON

H3
H3
ANTICIPATOR

AUX. HT.

W2

R

5

FAN
SWITCH

FALL
6

H2

EM. HT.

RISE
C1

W89
HEAT
PUMP
CONTROL
PANEL

B
EM. HT.
C1
ANTICIPATOR

RISE
C2

E

SYSTEM
SWITCH

8

C2
ANTICIPATOR

9
HEAT

EM. HT.
LED (YELLOW)
EM. HT. LIGHT

X

OFF

10

SERVICE
LED (RED)

COOL

L
11
O
Y
RESET
T

12

SERVICE LIGHT
COOL
CHANGEOVER
COMPRESSOR
LOW SPEED
OUTDOOR
RESET
M3952

Fig. 233. Schematic and hookup of T874W with Q674L. Used in heat pump applications.

THERMOSTAT

FALL

SUBBASE

SYSTEM COMPONENTS

COMPRESSOR
CONTACTOR

H1
ANTICIPATOR
1

H1
2

Y1

FAN
SWITCH

FAN RELAY

AUTO
G
4
FALL

R

8
RISE
CO

SYSTEM
SWITCH

1

W1
AUX. HT. RELAY
C

9

HEAT
AUX. HEAT
LED (RED)

OFF
10

1

L1
(HOT)

6

H2

RISE
C1

L2

ON

H2
ANTICIPATOR

C1
ANTICIPATOR

COOL

COOL
CHANGEOVER
VALVE

O

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

M3961

Fig. 234. Schematic and hookup of T874G with Q674B. Used in heat pump applications.

215

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

H1 ANTICIPATOR

R

2

RTD1

L1
(HOT)

OTD1

FAN
SWITCH

L2 1

3

FALL

H1

W2

ON
4

ODT2

H2
ANTICIPATOR

EHR2

AUX. HT.
LED (GRN)

5

SYSTEM
SWITCH

H2

FALL

EM. HT.
LED (RED)

OFF

RTD3

RTD1
X

SYSTEM
MONITOR

8
COOL

FAN
RELAY

L

9
RISE

RTD2

EHR1

AUTO

AUTO
G

HEAT

C1
ANTICIPATOR

CHANGEOVER

RD
COOL
CHANGEOVER VALVE

EM. HT.
10
O

RISE

EM. HT.
RELAY

C1
E
LACO

COMPRESSOR
CONTACTOR

CHP

Y
1

M7064

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

Fig. 235. Schematic and hookup of T874G and Q674F. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS
CONTROL MODULE

H1 ANTICIPATOR

1

W1

FAN
SWITCH

HEAT RELAY 1
W2

AUTO
FALL

H1

4

FALL

HEAT RELAY 2

HEAT DAMPER

ON

B
1

RH

6
H2 ANTICIPATOR

H2

RC

1
COOL DAMPER

8
C1
O

SYSTEM
SWITCH
RISE
9

OFF

10

AUTO

G
FAN RELAY

RISE

Y2

11

C2

SERVICE
LED (RED)

Y1

COMPRESSOR
RELAY 2

COMPRESSOR
RELAY 1

A
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
M7570

Fig. 236. Schematic and hookup of T874A-D with Q674C. Used in standard applications.

60-2485—8

216

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

SYSTEM COMPONENTS

SUBBASE

THERMOSTAT
H1 ANTICIPATOR

L1
(HOT)
L2

R
1

FAN SWITCH
1

AUTO

2

FAN RELAY

ON
FALL

G
3
H2 ANTICIPATOR

H1

B

4
LOW LED
(YELLOW)

5
SYSTEM
SWITCH

H2

FALL

6

HEAT

HI LED
(GREEN)

8

C1

HEAT 1
W1

HEAT 2

OFF
W2

RISE
COOL

10

COMPRESSOR
CONTACTOR

C1 ANTICIPATOR
Y
1

M7716

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

Fig. 237. Schematic and hookup of T874C with Q674B. Used in standard applications.

THERMOSTAT

H1
ANTICIPATOR

SUBBASE

1

X
FAN SWITCH

2
FALL

H1

SYSTEM COMPONENTS

CHECK
LED (RED)

AUTO
G
ON

FAN RELAY

L1
(HOT)

R
4
6

HEAT PUMP
RELAY

H2
ANTICIPATOR

SYSTEM
SWITCH

W1
AUX. HT.
RELAY

AUX. HT.

FALL
H2

W2

HT. PUMP
8

AUX. HT.
LED (RED)

2 STAGE HT.

C
OFF

C1

RISE

2

COOL

C1
ANTICIPATOR

COOL
CHANGEOVER
VALVE

O
10

1

L2 1

B RELAY
B

Y1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

COMPRESSOR
CONTACTOR

M7719

2 FACTORY INSTALLED JUMPER BETWEEN TERMINALS W1 AND Y1.

Fig. 238. Schematic and hookup of T874C with Q674F. Used in heat pump applications.

217

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1

G
FAN RELAY

H1
ANTICIPATOR

W

FAN SWITCH

2

AUX. HT.
LED (GREEN)

AUTO
H1

ON

EM. HT.
LED (RED)

FALL C1

H2

2

B
COMPRESSOR
MONITOR

3

F

4

R

FALL
5

SYSTEM
SWITCH

6

EM. HT.

AUX. HT.
RELAY

U

L1
(HOT)
OUTDOOR
SENSOR

L2

1

T

HEAT
X2

OFF
COOL
11

O

RESET

1

COOL
CHANGEOVER
OUTDOOR
VALVE
THERMOSTAT
COMPRESSOR
CONTACTOR

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

Y
M7744

2 FIELD REMOVABLE JUMPER.

Fig. 239. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

W1

1

H1
ANTICIPATOR

SYSTEM
OFF

HEAT
RELAY

2 ON
B

4

B RELAY

R
8

L1
(HOT)
L2

FAN

L1

L2

H1
FALL

K1

1

K1

LO
MED

C1
RISE
9

G1

K2

K2

K2

K1 RELAY

HI

HI

C1
ANTICIPATOR

G2
10

MED

LO

K2 RELAY
3 SPEED FAN SCHEMATIC

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

Y1
COMPRESSOR
CONTACTOR

2 FAN CONTINUOUS IN ON POSITION.

Fig. 240. Schematic and hookup of T874A with Q674W. Used in standard applications.

60-2485—8

218

M7745

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
H1
ANTICIPATOR

L2
FAN SWITCH

3

H1

L1
(HOT)

R

AUTO
4

FALL

1

Y

ON

FAN RELAY

COMPRESSOR
CONTACTOR

G

H2
ANTICIPATOR
5

W2

6

H2

HEAT
CHANGEOVER
VALVE NO. 1

SUPL. HEAT
LED (RED)
L
C

FALL
8

SYSTEM
SWITCH

C1
ANTICIPATOR

SUPL. HT.

9
CO

E

HEAT

HEAT
CHANGEOVER
VALVE NO. 2

10

RISE

HEAT
HEAT
CHANGEOVER CHANGEOVER
VALVE NO. 2
VALVE NO. 1

O.D.T.

OFF
11

COOL

HEAT
CHANGEOVER
VALVE NO. 3

X

C1
CO

P

X RELAY

RISE
12

P RELAY
O

1

COOL CHANGEOVER
VALVE

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M7742

Fig. 241. Schematic and hookup of T874J with Q674L. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

B
H1 ANTICIPATOR

1

HEAT DAMPER
FAN
SWITCH

W1
HEAT RELAY 1

AUTO
H1

FALL

G

ON

HEAT RELAY 2

4

FAN RELAY

W2
L1
(HOT)

6
R
SYSTEM
SWITCH

H2 ANTICIPATOR
H2
FALL

L2 1

OFF

8

S1
AUTO

2

C0

CHANGEOVER
VALVE

O

OVERRIDE

RISE

OVERRIDE
CIRCUIT

S2

9

OVERRIDE
CIRCUIT

C1 ANTICIPATOR
Y
SERVICE
LED (RED)

10

COMPRESSOR
RELAY

RISE
X

C1
1 POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

ON LED (YEL)
A

2 OVERRIDE IS MOMENTARY POSITION. SPRING RETURN TO (OFF)
UPON SWITCH RELEASE.

M7212

C

Fig. 242. Schematic and hookup of T874G with Q674C. Used in standard applications.
219

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1
FALL

H1 ANTICIPATOR

O
FAN SWITCH

COOL CHANGEOVER
VALVE

AUTO

2

G
ON

FAN RELAY

H1

B
B RELAY
4
L1
(HOT)

R

6

SYSTEM
SWITCH

H2
ANTICIPATOR

L2
E

OFF
EM. HT.

H2 FALL

1
EM. HT. RELAY

L
EM. HT.
LED (RED)

HEAT
AUTO
RISE

8
C1

2
X

COOL

AUX. HEAT
LED (GREEN)
AUX. HEAT RELAY

9
W2

C1 ANTICIPATOR

Y
10
11

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.

12

2

TERMINAL LABELED C/X ON SOME MODELS.

RISE

CO

COMPRESSOR
CONTACTOR
M7715

Fig. 243. Schematic and hookup of T874G with Q674F. Used in heat pump applications.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
H1
ANTICIPATOR

L2
3

H1

L1
(HOT)

R
FAN SWITCH
AUTO

4

FALL

1

Y

ON

COMPRESSOR
CONTACTOR

G

FAN RELAY

H2
ANTICIPATOR
5

W2

6

H2

HEAT
CHANGEOVER
VALVE NO. 1

SUPL. HEAT
LED (RED)
L
C

FALL
8
C1
ANTICIPATOR
CO

SYSTEM
SWITCH
E

SUPL. HT.
10

RISE

HEAT
HEAT
CHANGEOVER CHANGEOVER
VALVE NO. 2
VALVE NO. 1

O.D.T.
9

ON
11

OFF

HEAT
CHANGEOVER
VALVE NO. 2

HEAT
CHANGEOVER
VALVE NO. 3

X

C1
CO

P

X RELAY

RISE
12

P RELAY
O

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

COOL CHANGEOVER
VALVE

Fig. 244. Schematic and hookup of T874J with Q674J. Used in heat pump applications.

60-2485—8

220

M7743

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

H1/C1
ANTICIPATOR

SUBBASE

2

SYSTEM COMPONENTS

O
FAN SWITCH

COOL CHANGEOVER
VALVE

AUTO

3

G

H1

ON

FAN RELAY

C1

FALL

B
B RELAY

L1
(HOT)

R

4
6
H2
ANTICIPATOR

L2

SYSTEM
SWITCH

E

EM. HT.

L

HEAT

EM. HT.
LED (RED)

OFF

FALL

1
EM. HT. RELAY

2

H2

X

COOL

AUX. HT.
LED (GREEN)
AUX. HT. RELAY
1

W2

POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.

Y
COMPRESSOR
CONTACTOR

2 TERMINAL LABELED C/X ON SOME MODELS.

M7718

Fig. 245. Schematic and hookup of T874R with Q674L. Used in heat pump applications.

SUBBASE

THERMOSTAT

SYSTEM COMPONENTS

H1 ANTICIPATOR
1

H1

NO FAN
SWITCH

W1
HEAT RELAY 1
W2

FALL
4

HEAT RELAY 2
L2

6
SYSTEM
SWITCH

H2 ANTICIPATOR
H2

1

L1
(HOT)

OFF
FALL
8

C1

RH

AUTO
L1
(HOT)

RC
RISE

L2

9
1

1

10

Y1

11

Y2

COOL CHANGEOVER
VALVE

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

M7717

Fig. 246. Schematic and hookup of T874C with Q674G. Used in standard applications.

221

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

1
FALL
H1 ANTICIPATOR

T

H1
2
C815A OUTDOOR
THERMISTOR
H2

W3

H2 ANTICIPATOR

FALL

AUX. HT. RELAY

3
AUX. HEAT
LED (GREEN)

FAN SWITCH
AUTO

H3 ANTICIPATOR
4

G

ON

FAN RELAY

H3

L1
(HOT)
L2
1

R

FALL

5
EM. HEAT
LED (RED)

E

6

EM. HT. RELAY

RESET

X1
CHECK LED
(YELLOW)
C
CHANGEOVER
RELAY (HEAT)

RISE
8
C1

SYSTEM
SWITCH

CHANGEOVER
RELAY (COOL)

EM.HT.
9
HEAT
C1 ANTICIPATOR

2

B

O

OFF

10

X2

COOL

COMPRESSOR
CONTACTOR 1

C2 ANTICIPATOR

RISE

C2

11

Y1

12

Y2

COMPRESSOR
CONTACTOR 2

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

CONNECT CHANGEOVER RELAY TO 'O' TERMINAL FOR CHANGEOVER IN COOLING OR TO 'B' TERMINAL FOR CHANGEOVER IN HEATING.

Fig. 247. Schematic and hookup of T874W with Q674L. Used in heat pump applications.

60-2485—8

222

M6999

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2
FALL

H1

H1
ANTICIPATOR
3
4

H2

L1
(HOT)

R

FAN SWITCH

L2
AUTO

1

ON

L

H2 ANTICIPATOR

FAN RELAY

G

FALL

AUX. HT. RELAY

5
W2
7
E

RISE
C1

AUX. HT.
LED (RED)
8

SYSTEM
SWITCH

9

OFF

MALFUNCTION
LED (RED)

EM.HT. RELAY

C
HIGH SPEED
LED (YELLOW)

EM. HT.

C1
ANTICIPATOR

HEAT
10

C2
RISE

Y1

AUTO

C2
ANTICIPATOR
11

COMPRESSOR
CONTACTOR 2

COOL

CO

Y2
RISE

1

COMPRESSOR
CONTACTOR 1

LOW SPEED
LED (GREEN)

O

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

COOL
CHANGEOVER VALVE
M5923

Fig. 248. Schematic and hookup of T874Y with Q674F. Used in heat pump applications.

223

60-2485—8

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS
HEAT RELAY 1

FALL
W1

H1
1
H1 ANTICIPATOR

FAN
SWITCH

FAN RELAY
G

AUTO

3

ON
RC

2
HEAT RELAY 2

4
W2
6

HEAT DAMPER

FALL
B

H2 ANTICIPATOR

H2

SERVICE
LED (RED)
C

X
8

L1
(HOT) 1
L2

SYSTEM
SWITCH
RH

C1

HEAT
RISE
9

OFF

COOL DAMPER
O

COOL

C1 ANTICIPATOR
10

COMPRESSOR CONTACTOR 1
Y1

C2 ANTICIPATOR

RISE

COMPRESSOR CONTACTOR 2
11

Y2

C2
1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

2

FIELD WIRE JUMPER TO ALLOW SINGLE SYSTEM TRANSFORMER.

M18622

Fig. 249. Schematic and hookup of T874C with Q674B. Used in heat pump applications.

Home and Building Control Home and Building Control
Honeywell
1985 Douglas Drive North
Golden Valley, MN 55422

60-2485—8

Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
Scarborough, Ontario
M1V 4Z9

J.H. Rev. 3-01

Printed in U.S.A. on recycled
paper containing at least 10%
post-consumer paper fibers.

www.honeywell.com



---

Source Exif Data:

File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
PDF Version                     : 1.4
Linearized                      : Yes
Encryption                      : Standard V1.2 (40-bit)
User Access                     : Print, Copy, Fill forms, Extract, Assemble, Print high-res
Subject                         : Product Data
Modify Date                     : 2002:05:30 11:09:11-04:00
Create Date                     : 1999:07:07 12:30:47Z
Page Count                      : 224
Page Mode                       : UseOutlines
Producer                        : Acrobat Distiller 4.05 for Windows
Author                          : HBC Technical Communications
Mod Date                        : 2002:05:30 11:09:11-04:00
Creation Date                   : 1999:07:07 12:30:47Z
Metadata Date                   : 2002:05:30 11:09:11-04:00
Description                     : Product Data
Creator                         : HBC Technical Communications
Title                           : 60-2485 - T874 Multistage Thermostats and Q674 Subbases

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