LENNOX Controls And HVAC Accessories Manual L0806365

User Manual: LENNOX LENNOX Controls and HVAC Accessories Manual LENNOX Controls and HVAC Accessories Owner's Manual, LENNOX Controls and HVAC Accessories installation guides

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HEAT PUMPS
KITS AND ACCESSORIES

echnica
blication
Lithe

U.S.A.

,t_ 1993 Lennox industries Inc.
Dallas, Texas, USA

FM21 TMHEAT PUMP CONTROL
SLC1 SERVICE LIGHT KI'I"

502,826M
5/93
Supersedes 1/93

INSTALLATION

INSTRUCTIONS
FOR SERVICE LIGHT
LENNOX FM21 TMSYSTEM

OPTION

FOR USE WITH

4 - Wire thermostat terminal "L" to the '%STAT" terminal on the SLC1 board using thermostat wire. See
figure 1.
5 - Make wire connection from "L" wire d heat pump to
the "L HP" terminal on the SLC1 board with thermostat wire, Heat pump units may or may not have terminal strips; refer to heat pump wiring diagram for
location and color of service light "L" wire.

Package 1 of 1 contains:
1 - SLCl-service light control board
(with stand-offs)

Some heat pump thermostats are equipped with a service light which comes on if the heat pump fails to start
or if it has lost its charge. The light is controlled by the
service light control thermostat located in the heat
pump, The control thermostat closes if the compressor is not operating or if the heat pump has lost the refrigerant, Because the control thermostat is always
closed for a short time after a call for heat, most room
thermostats are wired so that the service light will not
be allowed to turn on until the second stage of heating
is called (W1).
By design, the FM21 will turn off the heat pump when
there is a call for second stage heat (W1). If the service
light control thermostat in the outdoor unit were wired
directly to the indoor thermostat, the light would be
falsely energized during second stage heating, The
SLC 1 allows the use of standard thermostats with service lights by latching on a relay if the service light control thermostat is still closed 5-1/2 minutes after a call
for heat (Y1). If later there is a call for second stage
heat(W1 ) and the relay is latched, the service light will
turn on indicating a problem with the heat pump,
It is important to note that for the SLC1 to operate, the
service light thermostat located in the heat pump
MUST be connected to common. (When the thermostat closes, the "L" terminal is connected to the 24VAC
common). Lennox heat pumps are factory wired this
way.

FM21 SLC1 SERVICE LIGHT CONTROL
I

BOARD
I FMC1
PLucs'"T°

(_

L#_#
&4,/I rj

Wireto

_

_

L terminal

of room therm_/

//

TYP

TYP

It

Wire to "L" terminal/wire

!_

in heat pump unit

FIGURE 1
6 - Locate jumper JR3 on the SLC1 board. This jumper
must be set according to the typical thermostat
used. Ifa GE thermostat is used, the jumper should
be across pins 3 and 2. Ifa White Rodgers thermostat is used, the jumper should be across pins 2 and
1. Refer to table 1 to identify thermostat as GE or
White Rodgers. See figure 2 for wiring examples.
TABLE 1
FM21 SERVICE LIGHT KIT JUMPER SETTING
Room
Thermostat
Lennox Part No•

JR3 SETTING
White Rodgers
(Pins 2 & 1)

43H98

p,,

18H12

p,,
p,,

18H13

GE
(Pins 3 & 2)

51 H46
51 H43
91 H72

1 - Disconnect electrical power,
2 - Insert pins from the SLC1 board into the plug location on the FM21 board. The connection will click
into place when secure.
3 - Insert stand-offs into provided holes in Fuelmaster
mounting box.

91 H73
43H99
27H30"
*Connect terminal 'L STAT" of FM21 to terminal "Xl" of 27H30 thermostat. Do NOT Use 'L" terminal on 27H30. Connect terminal 'X2" of
27H30 to terminal 'C" of 27H30.

Page 1

THERMOSTAT

WIRING

G.E. Typical

W.R. Typical

Thermostat

Thermostat
Internal

Internal
Wiring

Wiring

L STATrFL_

L

_

•'sm

JR3 Jumper
Over Pins 3 & 2.

s,c,
H(_P[_

L STATi2

;o

JR3 Jumper
Over Pins 1 & 2.

SLCl
k

Outdoor Unit

H

Terminal
(Pigtail)

Outdoor

Unit

Terminal
(Pigtail)

Service
Light
Thermostat

_

_

Service
Light
Thermostat

Outdoor Unit
Terminal
(Pigtail)

TerminalUnit
Outdoor
(Pigtail)

FIGURE 2

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