Carrier 48Fk Users Manual

JK034-074 to the manual b8c92953-552a-4777-b4fa-4d09629d7b77

2015-01-24

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48FK,JK034-074
50FK,FY,JK,JY034-104
Variable-Air Volume Rooftop Units

Controls Operation,
and Troubleshooting
CONTENTS
Page
SAFETY CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . 2
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Rooftop Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
VAV Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Processor Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
• P1 — SUPPLY-AIR SET POINT
• P2 — ECONOMIZER POSITION
• P3 — RESET LIMIT
• P4 — DEMAND LIMIT
• P5 — ECONOMIZER MINIMUM POSITION
• P6 — WARM-UP SET POINT
• P7 — SASP RESET TEMPERATURE
• PROCESSOR BOARD OUTPUTS
• CONFIGURATION HEADER AND DIP SWITCH
ASSEMBLY
Relay Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Display Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Thermistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
• T1 — SUPPLY-AIR TEMPERATURE THERMISTOR
• T2 — RETURN-AIR TEMPERATURE THERMISTOR
• T3 — SATURATED CONDENSING TEMPERATURE,
CIRCUIT 1
• T4 — SATURATED CONDENSING TEMPERATURE,
CIRCUIT 2
• T10 — RESET TEMPERATURE
Compressor Operation . . . . . . . . . . . . . . . . . . . . . . . . . 7
• CONTROL RELAY (CR)
Accessory Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
• P3 — RESET LIMIT
• P5 — ECONOMIZER MINIMUM POSITION
• P6 — MORNING WARM-UP TEMPERATURE
Single-Step Demand Unit . . . . . . . . . . . . . . . . . . . . . . . 7
Demand Limit Control Module (DLCM) . . . . . . . . . . . . 7
Economizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
• ENTHALPY CONTROL
• DIFFERENTIAL ENTHALPY
Variable Frequency Drive (VFD) . . . . . . . . . . . . . . . . . 12
Temperature Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
CONTROLS INSTALLATION . . . . . . . . . . . . . . . . . . . 13-25
Control Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
• NIGHT SETBACK THERMOSTAT
• SPACE TEMPERATURE RESET ACCESSORY
(50DJ900021)
Space Temperature Reset . . . . . . . . . . . . . . . . . . . . . . 13
• INSTALLATION
• CONFIGURATION
• OPERATING SEQUENCE
Demand Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
• SINGLE-STEP DEMAND LIMIT
• TWO-STEP DEMAND LIMIT
• INSTALLATION
• CONFIGURATION
• OPERATING SEQUENCE
Control From Remote Building Management
System (BMS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
• OCCUPIED/UNOCCUPIED

Page
•
•
•
•
•
•

NIGHT SETBACK CONTROL
UNIT SUPPLY AIR SET POINT ADJUSTMENT
DEMAND UNIT (1-STAGE OR 2-STAGE)
SUPPLY DUCT PRESSURE SET POINT ADJUSTMENT
EXTERNAL ALARM SIGNAL
REMOTE ECONOMIZER CONTROL
Smoke Control Modes . . . . . . . . . . . . . . . . . . . . . . . . . 21
• FIRE SHUTDOWN MODE
• PRESSURIZATION MODE
• EVACUATION MODE
• SMOKE PURGE MODE
• INSTALLATION
• CONFIGURATION
• OPERATING SEQUENCE
Air Pressure Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
• INLET GUIDE VANES
• VARIABLE FREQUENCY DRIVE
• MODULATING POWER EXHAUST
START-UP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-30
Initial Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Configuration Header . . . . . . . . . . . . . . . . . . . . . . . . . 26
DIP Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Adjusting Set Points . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Potentiometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Supply Fan Control with IGV Option . . . . . . . . . . . . . 28
Supply Fan Control with VFD Option . . . . . . . . . . . . 28
Modulating Power Exhaust
(Option or Accessory) . . . . . . . . . . . . . . . . . . . . . . . 30
START UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-34
Quick Test Program . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
OPERATING INFORMATION . . . . . . . . . . . . . . . . . . . 34-43
Digital Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
• CODES 0 THROUGH 8, CAPACITY STEPS
• CODES 20 THROUGH 30 AND 88, OPERATIONAL
STATUS
• CODES 51 THROUGH 87, DIAGNOSTIC
INFORMATION
Operating Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . 35
• SIZE 034, 038 AND 048-088 UNITS
• SIZE 044 UNITS
• SIZE 104 UNITS
Head Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . 36
Supply Fan Control with IGV . . . . . . . . . . . . . . . . . . . 38
Supply Fan Control with VFD . . . . . . . . . . . . . . . . . . . 38
Modulating Power Exhaust (Option or
Accessory Except FY,JY Units) . . . . . . . . . . . . . . . 38
Unit Staging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . 44-57
Checking Display Codes . . . . . . . . . . . . . . . . . . . . . . . 44
Complete Unit Stoppage . . . . . . . . . . . . . . . . . . . . . . . 44
Single Circuit Stoppage . . . . . . . . . . . . . . . . . . . . . . . 44
Restart Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Diagnostic Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
• CODES 51, 52, 55, 56: COMPRESSOR FAILURE

Manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice and without incurring obligations.
Book 1 1
PC 111
Catalog No. 534-716
Printed in U.S.A.
Form 48/50F,J-1T
Pg 1
4-99
Replaces: 48/50D,F,J-1T
Tab 1a 1b

CONTENTS (cont)

GENERAL
Page

IMPORTANT: This literature contains controls,
operation, and troubleshooting data for 48FK,JK and
50FK,FY,JK,JY variable air volume rooftop units. Use
this guide in conjunction with the separate Installation
Instructions literature packaged with the unit.

•
•
•
•

CODES 59 AND 60: LOW-PRESSURE SWITCH
CODES 63 AND 64: OIL PRESSURE SWITCH
CODE 70: ILLEGAL UNIT CONFIGURATION
CODES 71 TO 76: THERMISTOR/RESISTOR
FAILURE
• CODE 81: RESET THERMISTOR OR
POTENTIOMETER FAILURE
• CODE 82: LEAVING-AIR TEMPERATURE SET POINT
POTENTIOMETER FAILURE
• CODE 83: ECONOMIZER FEEDBACK
POTENTIOMETER FAILURE
• CODE 84: RESET LIMIT POTENTIOMETER
FAILURE
• CODE 85: DEMAND LIMIT POTENTIOMETER (P4)
FAILURE
• CODE 86: MINIMUM POSITION ECONOMIZER
POTENTIOMETER FAILURE
• CODE 87: WARM-UP TEMPERATURE SET POINT
FAILURE
Thermistor Troubleshooting . . . . . . . . . . . . . . . . . . . . 47
Electronic Controls Checkout . . . . . . . . . . . . . . . . . . 47
• PROCESSOR BOARD CHECKOUT
• RELAY BOARD TROUBLESHOOTING
• DISPLAY BOARD CHECKOUT
• ACCESSORY BOARD CHECKOUT
• TWO-STEP DEMAND LIMIT CONTROL MODULE
(DLCM) TROUBLESHOOTING
Enthalpy Sensor Checkout . . . . . . . . . . . . . . . . . . . . . 51
Economizer Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Variable Frequency Drive . . . . . . . . . . . . . . . . . . . . . . 52
• STANDARD TRANSDUCER CONTROL
• EXTERNAL SIGNAL CONTROL
• SUPPLY FAN MOTOR OVERLOAD PROTECTION
VFD Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
VFD Operational Status . . . . . . . . . . . . . . . . . . . . . . . . 54
Restoring Factory VFD Defaults . . . . . . . . . . . . . . . . 54
Unit Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Carrier 48FK,JK and 50FK,FY,JK,JY units provide ventilation, cooling, and heating (when equipped) in Variable
Air Volume (VAV) applications. These units contain factoryinstalled controls which provide full system management.
The unit controls also perform self diagnostic tests at unit
start-up, monitor operation of the unit, and provide alarms.
Information on system operation and status are sent to the
central processors by various sensors that are located at the
unit and in the conditioned space. Each unit is equipped with
a display board.

Rooftop Information — The rooftop controls cycle
supply-fan motor, compressors, and unloaders to maintain
the proper temperature conditions. The controls also cycle
condenser fans to maintain suitable head pressure. Safeties
are continuously monitored to prevent the unit from operating under abnormal conditions. The controls provide control of economizer and cycle or control heating as required.
The controls also allow the service person to operate a
‘quick test’so that all the controlled components can be checked
for proper operation.
IMPORTANT: The field-supplied and installed switch
(or timeclock) MUST BE CLOSED to put unit into
the Occupied mode. Unit WILL NOT START until this
is accomplished. See base unit installation instructions
literature for details.

VAV Control System — The 30 to 100-ton VAV rooftop units contain a microprocessor-based electronic control
system that controls and monitors the rooftop unit functions.
The VAV control system is composed of several components:
• processor board
• relay board
• display board
• thermistors
• compressor operation feedback (control relay)
• accessory board
• temperature reset package*
• single-step demand limit*
• two-step demand limit control module*
*Field-installed accessories.
The VAV control system monitors and controls the following functions of the rooftop unit:
• supply-air temperature (unit capacity)
• morning warm-up or electric heat (if equipped)
• head pressure control, fan cycling
• economizer position
• diagnostic display
• unit check-out (quick test)
• supply air temperature reset (if equipped)
• demand limiting (if equipped)

START-UP CHECKLIST . . . . . . . . . . . . . . . . . . CL-1, CL-2

SAFETY CONSIDERATIONS
Installing, starting up, and servicing this equipment can
be hazardous due to system pressures, electrical components; and equipment location (roof, elevated structures, etc.).
Only trained, qualified installers and service mechanics should
install, start up, and service this equipment.
When working on this equipment, observe precautions in
the literature; on tags, stickers, and labels attached to the equipment, and any other safety precautions that apply. Follow all
safety codes. Wear safety glasses and work gloves. Use care
in handling, rigging, and setting this equipment, and in handling all electrical components.

Electrical shock can cause personal injury and death.
Shut off all power to this equipment during installation
and service. There may be more than one disconnect
switch. Tag all disconnect locations to alert others not
to restore power until work is completed.

Processor Board — The processor board, shown in
Fig. 1, contains the logic and the necessary hardware to drive
the outputs and the display board. The processor board is
enclosed by a sheet metal cover and a heater. The heater is
controlled by a thermostat to keep the processor temperature
above 32 F (0° C). All electrical connections are made to the
processor board through wire and ribbon cables.

This unit uses a microprocessor-based electronic control system. Do not use jumpers or other tools to short
out components, or to bypass or otherwise depart from
recommended procedures. Any short-to-ground of the
control board or accompanying wiring may destroy the
electronic modules or electrical components.

LEGEND
DIP
— Dual In-Line Package
EPROM — Erasable, Programmable Read-Only Memory
EXV
— Electronic Expansion Valve

*EPROM HT204485-1-XX where ‘‘XX’’ is the current revision
number.
NOTE: Processor Board is positioned in unit with J3 and J10 connections at the bottom.

Do not remove label covering EPROM. Removal causes program to be erased.

Fig. 1 — Processor Board
Several temperature inputs are connected to the processor. There are either 4 or 5 thermistors (depending on the
field-installed accessories) which input temperature data
into the processor through pin terminal connector J1. See
Table 1 and Fig. 2.
Several status switches are also monitored. These switches
are connected to the processor at pin terminal connector J2.
See Fig. 3 and Table 2.

In addition to the unit status switch inputs, the processor
board also accepts inputs from several potentiometers. These
potentiometers control various operational characteristics of
the system. Inputs are received by the processor through pin
terminal connector J3. See Fig. 4.
All of the potentiometers must be set before the unit is
started in order for the unit to function properly. See StartUp, Potentiometers section on page 28 for information on
establishing set points. Each of the potentiometers has a valid
range that is used by the control. The valid range is defined
as the potentiometer’s resistance value that the control will
not consider to be in error. This is usually between 10% and
90% of the potentiometer’s total resistance. The control has
been programmed to accept an operational range for the potentiometer, which may not be the same as the valid range.

Table 1 — Pin Terminal Connector J1
Thermistor Inputs
CONNECTOR J1
TERMINAL NO.
1,2
14,15
16,17
18,19
20,21

TEMPERATURE
INPUT
Reset Temperature*
Saturated Condensing
Temp., Circuit 2
Saturated Condensing
Temp., Circuit 1
Return-Air Temperature
Supply-Air Temperature

UNIT SIZE
034-104
T10
T4
T3
T2
T1

LEGEND
T — Thermistor
*If equipped with accessory temperature reset package.
NOTE: Terminal numbers 3-13 are not used on these units.

LEGEND
CR — Control Relay
EC — Enthalpy Control
LPS — Low-Pressure Switch

LEGEND
— Thermistor
Field Wiring
Accessory

Fig. 3 — Pin Terminal Connector J2
Status Switch Inputs

Fig. 2 — Pin Terminal Connector J1
Thermistor Inputs

Table 2 — Pin Terminal Connector J2
Status Switch Inputs
CONNECTOR J2
TERMINAL NO.
1,2
3,4
7,8
9,10
13,14
15,20
15,24

STATUS SWITCH

UNIT SIZE
034-104

Oil Pressure,
Circuit 2

Jumpered

Oil Pressure,
Circuit 1
Loss Of Charge,
Circuit 2
Loss of Charge,
Circuit 1
Economizer
Changeover
Compressor Fault
Signal
Compressor Fault
Signal

Jumpered
LPS2
LPS1
EC
CR2
CR1
IN
P
RNT
SW

LEGEND
CR — Control Relay
EC — Enthalpy Control
LPS — Low-Pressure Switch
NOTE: Terminal numbers 5, 6, 11, 12, 16-19, and 21-23 are not used
on these units.

—
—
—
—

LEGEND
Input
Potentiometer
Return
Switch

Factory Wiring
Field Wiring
Accessory

Fig. 4 — Pin Terminal Connector J3
Potentiometer Inputs

The configuration header (part no. 30GB660001) is a
series of 8 small wires that are broken or unbroken in a
pattern to indicate several unique characteristics of the unit.
The configuration header is factory set and should not be
changed. Changing the factory setting may cause the unit to
malfunction.
The DIP switches configure the unit for several fieldinstalled options, as well as for several other options that
may be unique to the unit. The DIP switches are located under a plastic enclosure which must be removed for access.
The switches can be field adjusted, but must be adjusted only
when the unit control circuit breaker is off.

The potentiometer locations and functions are as follows:
P1 — SUPPLY-AIR SET POINT — This potentiometer is
located on the display board. The supply-air set point is the
cooling mode control temperature which the VAV control
system will attempt to maintain at Thermistor T1 by control of economizer position and/or cycling unloaders and
compressors.
P2 — ECONOMIZER POSITION — Economizer feedback
potentiometer is located on the economizer motor. The microprocessor is programmed to indicate an alarm if the travel
during initialization is less than 10% of the total potentiometer’s resistance. An alarm condition will also be signaled if
the potentiometer fails during operation, indicating that the
damper blades are stuck. If either situation occurs, the processor will try to drive the economizer dampers closed.
P3 — RESET LIMIT — This potentiometer is located on
the accessory board (provided standard from the factory) in
the unit main control box and establishes the maximum amount
of reset that can be applied to the supply-air set point (P1).
Reset is limited by the P1 default of 70 F. This potentiometer is used only when accessory, field-installed temperature
reset is used. If temperature reset is used, DIP (dual, in-line
package) switch 2 must be in the ON position.
P4 — DEMAND LIMIT — This potentiometer is located
near TRAN4 in the unit control box. The demand limit potentiometer is used only if accessory, field-installed demand
limit is used, and if DIP switch 5 is in the ON position. For
single-step demand limit, a field-installed 5 to 20 Kohm potentiometer and switch must be used.
P5 — ECONOMIZER MINIMUM POSITION — This potentiometer is on the accessory board (provided standard from
the factory) located in the unit main control box. This potentiometer specifies the minimum opening position for the
optional economizer. If a fault condition is detected by the
processor, an alarm condition will be signaled and the economizer dampers will close.
P6 — WARM-UP SET POINT — This potentiometer is on
the accessory board (provided standard from the factory)
located in the unit main control box. This potentiometer
establishes the set point temperature for the Morning
Warm-Up function. When the temperature is reached, Morning Warm-Up is terminated and VAV operation begins. DIP
switch 4 must be in the ON position if morning warm-up
heat is to be used.
P7 — SASP (SUPPLY AIR SET POINT) RESET TEMPERATURE — This 10 Kohm potentiometer is used only if
the accessory, field-installed temperature reset package is installed. This potentiometer determines the temperature at which
reset will begin. It is located on the accessory temperature
reset board. DIP switch 2 must be in the ON position to enable SASP reset.
PROCESSOR BOARD OUTPUTS — The processor board
also controls outputs through the relay board. The relay board
plugs into the processor board using a ribbon cable.
In addition, the processor board controls the display board.
The display board is connected to the processor board by a
ribbon cable, and has an LED (light-emitting diode) display
showing the status of the unit and diagnostic information.
CONFIGURATION HEADER AND DIP SWITCHASSEMBLY — The processor board is programmed to control a variety of air conditioning units. To tailor the processor to the
particular unit being controlled, 2 devices are used. One is
the configuration header, and the other is the DIP switch
assembly.

Relay Board — The relay board is used to control 24-v
and 115-v loads. See Fig. 5. The relay board is connected to
the processor board by a ribbon cable at pin J9. Electrical
connections to the relay board are made through pins J5
(115 v) and J6 (24 v). The relay board has eight 24-v relays
and five 115-v relays. See Table 3.
Display Board — The display board is located in the
main unit control box and is connected to the J10 port of the
processor board through a ribbon cable. The display board
contains the supply-air set point potentiometer P1; a 2-digit,
LED display; and the display button (see Fig. 6). The LED
display is used to convey the operating information and operational error codes.

Thermistors — The processor uses up to 5 thermistors
to sense the temperatures at various points in the system.
See Table 1 and Fig. 7-14. All the thermistors have identical
temperature versus resistance and voltage drop characteristics, and are monitored by the processor for a short or open
circuit. The valid range for a thermistor is 362,640 to
219 ohms. Thermistor details and locations are as follows:
T1 — SUPPLY-AIR TEMPERATURE THERMISTOR —
This thermistor is located in the unit supply fan discharge.
It provides information for the processor to stage the number of capacity steps required to maintain a desired supplyair temperature.
T2 — RETURN-AIR TEMPERATURE THERMISTOR —
This thermistor is located in the mixed-air portion of the unit
cabinet. The thermistor’s primary function is to provide morning warm-up information. This sensor will also provide differential information for the processor during cooling operation (such as the rate of change for a capacity step).
T3 — SATURATED CONDENSING TEMPERATURE, CIRCUIT 1 — This thermistor is located on the condenser coil
return bend. See Fig. 13 and 14. It controls the staging of the
unit condenser fans based on the condensing temperature of
the refrigerant at the designated position on the condenser
coil.
T4 — SATURATED CONDENSING TEMPERATURE, CIRCUIT 2 — This thermistor is located on the condenser coil
return bend. See Fig. 13 and 14. It controls the staging of the
unit condenser fans based on the condensing temperature of
the refrigerant at the designated position on the condenser
coil.
T10 — RESET TEMPERATURE — This thermistor is used
only if the accessory temperature reset package is used. It
provides occupied space temperature information to the processor, which determines whether or not reset is required.
The thermistor is remotely mounted outside the unit in the
conditioned space.

Table 3 — Output Pin and Terminal Assignments
OUTPUT PINTERMINAL

NAME

J6-1

Stage 1
Compressor Relay (K1)*
Stage 2
Compressor Relay (K2)*
Stage 3
Compressor Relay (K3)*
Stage 4
Compressor Relay (K4)†
Stage 5
Compressor Relay (K5)†
Stage 6
Compressor Relay (K6)†
Economizer Open Relay (K7)
Economizer Close Relay (K8)
Supply Fan Relay (K9)
Morning Warm-Up Relay (K10)
Stage 1 Condenser
Fan Relay (K11)
Stage 2 Condenser
Fan Relay (K12)
External Alarm Relay (K13)

J6-2
J6-3
J6-4
J6-5
J6-6
J6-7
J6-8
J5-1
J5-2
J5-3
J5-4
J5-5
ALM
CR
ECR
EOR
HIR
IFC
OFC
U

—
—
—
—
—
—
—
—

RATING

LEGEND
Alarm
Control Relay
Economizer Close Relay
Economizer Open Relay
Heat Interlock Relay
Indoor (Evaporator) Fan Contactor
Outdoor (Condenser) Fan Contactor
Unloader

DEVICE
CR1
U2**
U1

24 vac

Not Used
CR2
Not Used
EOR
ECR
IFC
HIR

115 vac

OFC2/OFC3 ††
OFC4 \
ALM

*Circuit 1.
†Circuit 2.
**U2 is not used on 044 units.
††OFC2 on 034-048 units; OFC3 on 054-104 units.
\ Used on 054-104 units only.

LEGEND
CR — Control Relay
J
— Terminal Pin Connectors
K — Relay

Fig. 5 — Relay Board

P1 SUPPLY AIR
SET POINT
POTENTIOMETER

TWO-DIGIT
DISPLAY

P3 — RESET LIMIT — The processor board is programmed
for occupied space temperature reset. In order for reset to
work, the accessory temperature reset board must be used.
Potentiometer P3 is the maximum set point temperature to
which the supply air can be reset.
P5 — ECONOMIZER MINIMUM POSITION — This potentiometer controls the set point for the minimum position
of the economizer.
P6 — MORNING WARM-UP TEMPERATURE — This potentiometer controls the morning warm-up temperature set
point.

DISPLAY
BUTTON

Single-Step Demand Limit — The single step demand limit provides a means to limit the capacity of the VAV
unit using an external switch. Single step demand limit will
limit the compressor displacement based on the ratio of the
wiper arm to the full scale resistance. The exact percentage
of capacity reduction differs depending on the number of capacity steps.
A 3-wire, 5 to 20 Kohm, field-supplied potentiometer (P4)
is required for this option. The potentiometer should be wired
to the processor J3 connections. In order to control the demand limit, the wiper arm of the potentiometer should be
switched open and closed based on the demand limit
requirement. The control switch is also field-supplied and
installed.
If the wiper arm wire is open, all capacity stages can be
used. When the wiper arm wire is closed, the capacity is
reduced by the amount set on potentiometer P4.

Fig. 6 — Display/Set Point Board

Compressor Operation
CONTROL RELAY (CR) — This relay provides information to the processor about compressor operation (one control relay per compressor). The relay controls and protects
the compressor and also controls the crankcase heater.
A control signal to check the safety statuses and to start
the compressor is sent from the relay board. This signal travels through all of the safeties: the high-pressure switch, and
the internal protector (where used) and on to the control relay coil. Once the control relay coil has been energized, the
control relay completes a feedback circuit for the processor,
informs the processor of the status of the compressor safeties, energizes the compressor contactor coil, and deenergizes the crankcase heaters. A fault will be detected by the
processor if the control relay opens during operation or startup. The processor will lock the compressor or the circuit off
by deenergizing the appropriate relay(s) on the relay board
and energizing an alarm signal.

Demand Limit Control Module (DLCM) — The
DLCM provides a 2-step demand limit control using an external switch. The first step is between 50% and 100% of the
maximum compressor displacement. See Fig. 16. The second step is between 0% and 49% of the maximum compressor displacement. The exact percentage differs depending on
the number of capacity steps.
Two adjustable potentiometers are used to set the 2 demand limit points. Potentiometer P1 is used to set a demand
limit between 50% and 100% of the unit capacity. Potentiometer P2 is used to set a demand limit between 0% and
49% of unit capacity.
If no power is supplied to the demand limit control module, all capacity stages can be used. When power is supplied
to terminal IN1 only, the first step of the demand limit control is energized and the capacity is reduced by the amount
set on potentiometer P1. When power is supplied to terminal
IN2 only, or to both IN1 and IN2, the capacity is reduced by
the amount set on potentiometer P2.

Accessory Board — The accessory board is standard
(factory supplied) in the VAV rooftop units. See Fig. 15. This
board is located in the control box of each unit. Each board
has a prewired connector supplied with it to connect directly
to the processor board. It has 3 potentiometers: P3, P5, and
P6.

GAS SECTION
(48FK,JK ONLY)

HORIZONTAL SUPPLY SECTION
(50FY,JY ONLY) AND EXTENDED
PLENUM SECTION (50FKX,FKY,JKX,JKY)

Fig. 7 — Thermistor T1 Location, 48FK,JK, 50FY,JY and 50FKX,FKY,JKX,JKY 034-048 Units

FAN DISCHARGE/ELECTRIC HEAT SECTION

Fig. 8 — Thermistor T1 Location, 50FK,JK034-048 Units
8

GAS SECTION
(48FK,JK)

HORIZONTAL DISCHARGE SECTION (50FY,JY)
AND EXTENDED
PLENUM SECTION (50FKX,FKY,JKX,JKY)

Fig. 9 — Thermistor T1 Location, 48FK,JK, 50JY and
50JKX,JKY 054-074 Units and 50FKX,FKY and 50FY054-104 Units

FAN DISCHARGE/ELECTRIC HEAT SECTION

Fig. 10 — Thermistor T1 Location, 50FK,JK054-074 Units
9

STANDARD
FILTERS

BAG
FILTERS

Fig. 11 — Thermistor T2 Location, Size 034-048 Units
Fig. 13 — Thermistor T3 and T4 Locations,
Size 034-048 Units

ENTHALPY CONTROL — Outside air enthalpy control is
standard with the factory-installed economizer option. Enthalpy is sensed by a controller located behind the end outside air hood. The control can be accessed by removing the
upper hood filter. See Fig. 17.
DIFFERENTIAL ENTHALPY — Added efficiencies in economizer control can be gained by installing a differential enthalpy sensor in the return air duct. When differential enthalpy
control is installed, the economizer control will use the air
stream with lower enthalpy (outside air or return air) to provide for lower compressor operating costs during integrated
economizer cycle operation. The differential enthalpy sensor is installed in the return-air duct.

STANDARD FILTERS

BAG FILTERS
(054-074 Only)

Fig. 12 — Thermistor T2 Location, Size 054-104 Units

Economizer — Economizer control is used to control
the outside and return air dampers of the unit, to satisfy space
cooling demand using all outside air (when permitted), and
to satisfy cooling in conjunction with compressor operation
(when conditions permit). During Occupied periods without
cooling demand, the outside-air dampers will be at the userconfigured Minimum Damper Position (at P5 on accessory
board). During Unoccupied periods, the outside-air dampers
will be closed.
The economizer is available as a factory-installed option.
The user can install an accessory differential enthalpy sensor
to enhance economizer control. Refer to the installation section for field wiring of the sensor.

054 UNITS

064, 074, 078 UNITS

088, 104 UNITS

Fig. 14 — Thermistor T3 and T4 Locations, Size 054-104 Units

Variable Frequency Drive (VFD) — The optional
VFD is used to modulate supply fan airflow to maintain duct
static pressure on VAV applications. The VFD is located in
the supply fan section (see Fig. 18 and 19), and can be accessed by opening the fan section access door.
The unit is supplied with a pressure transducer capable of
measuring from 0.0 to 5.0 in. wg. The pressure transducer
will send a 4 to 20 mA signal to the VFD to modulate the
speed of the indoor fan motor to precisely control the fan to
the desired static pressure set point. The VFD is factory set
at 2.5 in. wg duct static pressure. Refer to the Operating Sequence section for more information on the VFD.
The VFD has been programmed and wired at the factory
for this application. No further adjustments (except for Duct
Static Pressure Set Point) should be necessary at start-up.
Factory jumper wire configurations are shown in the Supply
Fan Control with VFD Option section on page 28.
A separate service manual for the factory-installed VFD
is supplied with each unit. Refer to the VFD manual for more
information on the VFD controls.

ECON
MIN
P
VAV

—
—
—
—

Temperature Reset — Accessory temperature reset allows the unit to automatically adjust (‘‘reset’’) the supplyair temperature set point to a higher value once most of the
space cooling load has been met. When the space conditions
are satisfied, the VAV terminals will close to the minimum
position. All VAV units will sense the decrease in actual supplyair temperature and the unit controls respond by reducing

LEGEND
Economizer
Minimum
Potentiometer
Variable-Air Volume

Fig. 15 — Accessory Relay Board
(Standard; Factory Supplied)

IC
IN
P
RTN

—
—
—
—

LEGEND
Integrated Circuit
Input
Potentiometer
Return

Fig. 16 — Two-Step Demand Limit Module

Fig. 18 — Variable Frequency Drive,
Sizes 034-048 and 078-104

Fig. 17 — Enthalpy Sensor Location
Fig. 19 — Variable Frequency Drive, Sizes 054-074
12

There are no required 115-volt field wiring connections,
therefore no provisions have been made in the unit for running 115-volt wiring. If any of the field-installed options requiring 115-volt connections are desired, the unit must be
modified in the field for 115-volt wiring.
NIGHT SETBACK THERMOSTAT — Wire field-supplied
thermostat (suitable for 24-v circuit) between terminals 1 and
2 on terminal block 3 (sizes 034-048) or terminal block 4
(sizes 054-104). This thermostat is used to bypass the timeclock occupied/unoccupied switch and is used to operate unit
during unoccupied times at more economical temperatures.
(See Fig. 23.)
SPACE TEMPERATURE RESET ACCESSORY
(50DJ900021) — Consists of a thermistor (T10) and a reset
board with a potentiometer (P7) that is used to set space temperature at which reset starts. Mount reset board in unit
control box or other convenient place. Wire thermistor in series with P7 and connect to terminals 12 and 15 on terminal
block 3 (sizes 034-048) or terminal block 4 (sizes 054-104)
in unit control box. If there is a long run to conditioned space,
it is necessary to splice additional wire to thermistor. The
reset board has 2 pressure connectors for field wiring. (See
Fig. 25).

capacity stages to maintain user-established supply-air set
point temperature. When VAV units are also equipped with
optional supply duct pressure controls (either inlet guide vanes
[IGV] or variable frequency drive package), the unit also senses
an increase in duct static pressure and responds by closing
IGV dampers or slowing fan wheel speed to maintain userconfigured set points for supply duct pressure. Allowing the
supply-air temperature to be reset to a higher value maintains air circulation in the space without costly overcooling.
The accessory package is required for temperature reset.
The accessory includes:
• thermistor T10, to monitor space temperature
• reset temperature potentiometer P7, to establish start temperature for reset operation
• reset limit potentiometer P3, to establish maximum level
of modified supply-air temperature
More than one space sensor may be used if an average
space temperature is desired for initiating temperature reset.
Refer to installation section for sensor part number and wiring schematic.
Temperature reset will start when space temperature (at
T10) drops to the set point at P7. When Temperature Reset
is active, the LED (light-emitting diode) display will show
code 21 . Automatic adjustment of supply-air temperature
set point will end when modified SASP equals reset limit set
point at P3. (See formula for automatic modification of SASP
in Controls Installation, Space Temperature Reset section on
this page.)

Space Temperature Reset
INSTALLATION — Install the accessory temperature reset
package in accordance with instructions provided with the
accessory kit.
Mount the reset board in the unit control box (or other
suitable location) per instructions.
Locate the thermistor T10 in a suitable location in the occupied space per instructions.
Wire T10 to the reset board and to the unit control terminal block per Fig. 25. Wire the other terminal on the reset
board to the unit control terminal block per Fig. 25.
If multiple sensors are required to average the space temperature, see Fig. 26. Use only Carrier Part Number
HH79NZ014 sensor, in arrangements of 4 or 9 sensors, with
total wiring not to exceed 1000 ft.
To enable reset function, change DIP (dual in-line package) switch 2 to position ON. (Disconnect control power before changing DIP switch positions; reconnect power after
all changes have been made.)
CONFIGURATION — Set points for reset operation are established at potentiometers P7 and P3 (on the reset board).
Potentiometer P7 — Reset temperature set point (temperature at which reset function will start). Maximum of 80 F,
minimum 0° F. Set below normal room cooling set point level
to sense overcooling in the occupied space.
NOTE: It is difficult to accurately set the P7 potentiometer
to the desired set point. Use the procedure below.
Proper setting of the P7 potentiometer may be made on a
resistance basis. The microprocessor initiates reset when it
detects a resistance of the thermistor plus the potentiometer
of 13,084 ohm. The potentiometer set point may be calculated using the following formula:
P7R = 13,084 – T10R

CONTROLS INSTALLATION
The VAV units may be used in applications with additional control features, options, or accessories. Refer to the
appropriate accessory installation instructions for more information on installing that accessory. Unit control box component arrangement is shown in Fig. 20-22. Control options
and accessories available for VAV units are:
• smoke control modes
• differential enthalpy sensor
• electric heaters (sizes 034-074 only)
• modulating power exhaust
• Motormastert I control
• space temperature reset
• night setback thermostat (field-supplied)
• single step demand limit
• two-step demand limit
• inlet guide vanes
• variable frequency drive
• variable frequency drive remote display kit

Control Wiring — A switch or timeclock (field supplied) must be wired in to control when unit will go into and
out of Occupied mode. Connect switch or timeclock between terminals 1 and 2 on terminal block 3 (sizes 034-048)
or terminal block 4 (sizes 054-104) in unit control box. See
Fig. 23. The circuit potential is 24 v.
Variable air volume units equipped with warm-up heat require that room terminals be controlled to go fully open when
unit goes into the Heating mode. Heating interlock relay (HIR)
is provided for this function. The relay is located in the unit
control box. When unit goes into Heating mode, interlock
relay is energized providing switch closure or opening (depending on how field power source is set up) to open the
room terminals. Field connections for interlock relays are
terminals 3 and 4 (for normally open contacts) and terminals
3 and 7 (for normally closed contacts) on terminal block 3
(sizes 034-048) or terminals block 4 (sizes 054-104). See
Fig. 24. Note that a field-supplied power source is required.

Where:
P7R = the desired set point of the P7 potentiometer in ohms
T10R = the resistance of the T10 thermistor for the desired
set point

14
Fig. 20 — Unit Control Box Arrangement, Sizes 034-048

15
Fig. 21 — Unit Control Box Arrangement, Sizes 054-078

16
Fig. 22 — Unit Control Box Arrangement, Sizes 088 and 104

034-048: TB3
054-104: TB4

Control will automatically adjust leaving air temperature by
the following formula:
MSP = SP + [(P3 - SP) / 3] x (P7 − T10)
where:
MSP = Modified Leaving-Air Set Point
SP = Supply-Air Set Point
P3 = Maximum Supply-Air Temperature (reset limit)
P7 = Reset Initiation Temperature (reset set point)
T10 = Actual Space Temperature
3
= Ratio for reset (F) (fixed parameter)

034-048: TB3
054-104: TB4

OCCUPIED/UNOCCUPIED
SWITCH

NIGHT SETBACK THERMOSTAT

Table 4 — Thermistor Resistance and
Voltage Drop Characteristics

NOTES:
1. Occ/Unocc switch closes when occupied.
2. Night setback thermostat closes when in night setback heating.

TEMP
(F)
31.0
32.0
33.0
34.0
35.0
36.0
37.0
38.0
39.0
40.0
41.0
42.0
43.0
44.0
45.0
46.0
47.0
48.0
49.0
50.0
51.0
52.0
53.0
54.0
55.0
56.0
57.0
58.0
59.0
60.0
61.0
62.0
63.0
64.0
65.0
66.0
67.0
68.0
69.0
70.0
71.0
72.0
73.0
74.0
75.0
76.0
77.0
78.0
79.0
80.0

Fig. 23 — Occupied/Unoccupied Switch with
Night Setback Thermostat
034-048: TB3
054-104: TB4
3

FIELD
SUPPLIED
POWER
SOURCE

N.O.
SIGNAL
TO ROOM
TERMINALS

N.C.

Fig. 24 — Heat Interlock Relay
034-048: TB3
054-104: TB4
T10
12
P7

RESET
BOARD

Fig. 25 — Accessory Reset Board

EXAMPLE:
T10 desired set point is 70 F.
T10R from Table 4 for 70 F is 5929 ohms.
P7R = 13,084 – 5929
P7R = 7155 ohms
Using an ohmmeter, set the P7 potentiometer to
7155 ohms to achieve a reset initiation set point of 70 F.
Potentiometer P3 — Reset limit set point (maximum temperature value for modified supply air set point). Maximum
of 70 F, minimum 40 F. Set between leaving air set point
(P1) and 70 F (maximum range permitted by control).
OPERATING SEQUENCE — If space temperature is above
reset set point (T10 > P7), no reset will occur.
If space temperature is equal to or less that reset set point
(T10 < P7), the LED will display 20 and reset will begin.

RESISTANCE
(Ohms)
16813.8
16345.7
15892.2
15452.7
15026.7
14613.9
14213.6
13825.5
13449.2
13084.2
12730.1
12386.6
12053.3
11730.0
11416.1
11111.5
10815.8
10528.7
10250.0
9979.3
9716.5
9461.3
9213.4
8972.6
8738.6
8511.4
8290.6
8076.1
7867.7
7665.1
7468.3
7277.1
7091.2
6910.6
6735.1
6564.4
6398.6
6237.5
6080.8
5928.6
5780.6
5636.8
5497.0
5361.2
5229.1
5100.8
4976.0
4854.8
4736.9
4622.4

VOLTAGE
DROP (v)
3.582
3.553
3.523
3.494
3.464
3.434
3.404
3.373
3.343
3.312
3.281
3.250
3.219
3.187
3.156
3.124
3.093
3.061
3.029
2.997
2.965
2.933
2.901
2.869
2.837
2.805
2.772
2.740
2.708
2.676
2.644
2.612
2.581
2.549
2.517
2.486
2.454
2.423
2.391
2.360
2.329
2.299
2.268
2.237
2.207
2.177
2.147
2.117
2.088
2.058

RED
BLK

RED
BLK
SIZES 034-048
TB3
RED
12
BLK
15

RED

BLK

TO ACCESSORY SPACE
TEMPERATURE RESET
CONTROL BOARD
SIZES 054-104
TB4
12
15

SENSOR 1

SENSOR 2

SENSOR 3

SENSOR 4

SPACE TEMPERATURE RESET — 4 SENSOR AVERAGING APPLICATION
SIZES 034-048
TB3
12
15

RED
BLK

SIZES 054-104
TB4
12

RED

BLK

TO ACCESSORY SPACE
TEMPERATURE RESET
CONTROL BOARD

SENSOR 1

RED

BLK

SENSOR 5

SENSOR 6

RED

BLK

SENSOR 4
NOTE: Sensor part number is HH79NZ014.

SENSOR 3

SENSOR 2

SENSOR 7

RED

BLK

SENSOR 8

SENSOR 9

SPACE TEMPERATURE RESET — 9 SENSOR AVERAGING APPLICATION

Fig. 26 — Space Temperature Sensor Averaging

Control Module kit plus installation of 2 field-supplied control switches (SPST-NO each). This accessory control provides for a first step reduction of 50% to 100% of the maximum compressor staging; the second step provides for reduction
between 0% and 49%. The exact percentage of capacity reduction differs depending on the number of capacity steps.
When demand limit is active, the LED display will show
code 22 .

Demand Limit — The demand limit function provides
a means to limit the cooling capacity of the VAV unit using
an external discrete switch function. When enabled by the
closure of the external switch, the control will limit the available compressor staging capacity according to user set points
established at demand limit potentiometer(s).
The unit controls support two types of demand limit: singlestep and 2-step control.
SINGLE-STEP DEMAND LIMIT — This function will limit
the total compressor staging based on the ratio of the set point
potentiometer’s wiper arm position to the full scale resistance of the potentiometer. The exact percentage of capacity
reduction differs depending on the number of capacity steps.
A field-supplied potentiometer and control switch are required for this function. See installation section for specification on potentiometer and field wiring.
TWO-STEP DEMAND LIMIT — Two-step demand limit is
provided with the installation of the accessory Demand Limit

INSTALLATION
Single-Step Demand Limit — A 3-wire 5 to 20 K-ohm potentiometer must be field-supplied and installed. A singlepole normally open switch is also required (field-supplied
and -installed). Locate the potentiometer (designated P4) and
the switch in a suitable location (external from the unit or in
the unit control box).

Connect the potentiometer end terminals to terminals 8
and 9 on control terminal block TB3 (sizes 034-048) or TB4
(sizes 054-104) (see Fig 27). Connect the switch terminals
to the potentiometer wiper arm terminal and to terminal 10
on TB3 or TB4.
To enable demand limit function, change DIP switch 5 to
position ON. (Disconnect control power before changing DIP
switch positions. Reconnect power after all changes have been
made.)
Set the potentiometer P4 to desired capacity reduction value.
Two-Step Demand Limit — Install the demand limit control module (DLCM) according to the installation instructions provided with the accessory. Disconnect existing leads
at connector J3 on the processor board (see instructions) and
connect the plug from the DLCM harness to connector J3.
Connect the field input control power wires (from the external control relays) at the terminal strips marked IN1, RTN1,
IN2 and RTN2 (see Fig. 28 and 29).
To enable demand limit function, change DIP switch 5 to
position ON. (Disconnect control power before hanging DIP
switch positions. Reconnect power after all changes have been
made.)
Set the potentiometers DLCM-P1 and DLCM-P2 to desired capacity reduction values.
Check the operation of demand limit function by using
the Quick Test procedures.
CONFIGURATION
Single-Step Demand Limit — Field-installed potentiometer P4 establishes capacity reduction value for demand limit
operation. Set this potentiometer between 0% and 100%. The
exact percentage of capacity reduction differs depending on
the number of capacity steps.
Two-Step Demand Limit — Potentiometer P1 and P2 (located on the accessory demand limit control module) establish the capacity reduction values for each step of demand
limit. Set potentiometer DLCM-P1 between 50% and 100%.
Set potentiometer DLCM-P2 between 0% and 49%. The exact percentage of capacity reduction differs depending on the
number of capacity steps.
OPERATING SEQUENCE
Single-Step Demand Limit — If the field control switch to
the wiper arm terminal is open, all capacity stages will be
available (no demand limit in effect). When the field control
switch is closed, the compressor cooling capacity is reduced
by the amount set on potentiometer P4.
When demand limit is in effect, the LED display will show
code 22 . If a potentiometer setting or input is out of range,
the control will terminate the demand limit function and show
code 84 at the display LED.
Two-Step Demand Limit — If the field control switches are
both open (no power supplied to the Demand Limit Control
Module), all capacity stages will be available (no demand
limit in effect). When control power is supplied to terminal
IN1 only (field switch SW1 closes), the first step of the demand limit is energized and the compressor cooling capacity
is reduced by the amount set on potentiometer DLCM-P1.
When control power is supplied to terminal IN2 (field switch
SW2 closes), the second step of the demand limit is energized and compressor cooling capacity is reduced by the amount
set on potentiometer DLCM-P2.
When demand limit is in effect, the LED display will show
code 22 . If a potentiometer setting or input is out of range,
the control will terminate the demand limit function and show
code 84 at the display LED.

034-048: TB3
054-104: TB4
8

5-20K
POTENTIOMETER
(P4)

10
SWITCH

Fig. 27 — Single-Step Demand Limit

Fig. 28 — Two-Step Demand Limit Module

NOTES:
1. Demand limit switches are field supplied and wired.
2. Demand limit control module terminal blocks will accept up to
12-gage wire.
is field wiring.
3.

Fig. 29 — 115-Volt Field Wiring to Accessory
2-Step Demand Limit Control Module

Control From Remote Building Management System (BMS) — The unit control system is not a communicating control system, and it cannot be accessed directly
by a DDC (Direct Digital Control) control system (or by a
BACnet communication system). However, it is possible to
control some functions of these units via 4 to 20 mA or 2 to
10 vdc signals and discrete inputs (relay contact closures).
Functions that can be managed from or accessed from an
external control system include:
• Occupied/Unoccupied Status
• Night Setback Control
• Unit Supply Air Set Point Adjustment
• Demand Limit (1-stage or 2-stage)
• Supply Duct Pressure Set Point Adjustment
• External Alarm Signal
Remote control of the economizer cycle on these units is
not recommended. Refer to the Operating Sequence section
on page 35 for a discussion on the economizer cycle
operation.

OCCUPIED/UNOCCUPIED — The unit control system will
initiate normal occupied mode functions (including Morning Warm-up, Economizer Minimum Position, and Cooling
Cycle) whenever a contact closure is made that emulates the
normal timeclock contacts. See Fig. 23. (‘‘Occupied/Unoccupied
Switch’’). The contact closure from the BMS must be an isolated contact set, normally open, and suitable for 24-volts
AC pilot duty.

Configuration — Configure as follows:
1. Set DIP switch no. 2 to ON.
2. Adjust manual potentiometer to 12.6 to 12.8 k-ohm.
3. Configure transducer for job site input signal from BMS.
4. Adjust Potentiometer (P3) on the rooftop to MAXIMUM
SASP value (typically 65 to 70 F). The maximum P3 SASP
control limit is 70 F.
Operation —Unit will initiate SASP Reset (adjust configured SASP upward) when the sum of the resistance (fixed
resistance + potentiometer + transducer) exceeds 13.1 k-ohm.
Once reset is initiated, full range of reset (P3 setting minus
configured SASP) will be reached with 500-ohm increase in
transducer resistance (TR).
During Reset mode operation, Code 21 will appear on unit
display board.
Formula:
MSP = SASP +

NIGHT SETBACK CONTROL — Night setback control is
used to control the space to a set point level that is typically
lower than during normal occupied periods (Heating Only
mode). Some applications also require a limitation on the
maximum space temperature during unoccupied periods (Cooling mode). Both modes are possible by closing the same contacts used in the Occupied/Unoccupied control, or by installing
a dedicated contact set in parallel with the Occupied/
Unoccupied control contacts, and using the BMS space temperature sensing system and its logic to determine when to
initiate unit operation.
Once the unit operation has been initiated by the BMS
contact closure, the unit operates in its normal occupied mode
manner, initiating morning warm-up if needed (as sensed by
return air temperature to the unit) or cooling (controlling to
current SASP value). The Night Setback Control contacts
will interrupt normal unit operation when the BMS senses
that space temperatures have returned to unoccupied set point
levels, and the unit will shutdown normally.
The contact closure from the BMS must be an isolated
contact set, normally open, suitable for 24-volts AC pilot duty.
NOTE: If the rooftop unit is equipped with a VFD and night
setback cooling operation is intended, the fan system must
be controlled to permit FULL SUPPLY FAN AIR DELIVERY during unoccupied cooling operation. This is most conveniently attained by replicating the HIR relay function of
the rooftop unit. An HIR control sequence will force all room
terminals to their minimum heating CFM position, thus assuring adequate airflow through the rooftop unit during night
setback cooling operation. During night setback cooling operation, the return-air temperature (RAT) will be well above
normal levels. The higher RAT means that the air temperature leaving the evaporator coil will also be well above normal levels. This situation is interpreted by the unit control
system as a demand for additional cooling stages. The unit
control responds to this demand by bringing on more stages,
until typically all stages are active. If the VFD is not working in-step with the refrigeration system demand, it is possible to produce low suction pressures and local frosting
on the evaporator coil during the night setback cooling
operation.

[

(P3 − SASP)
(3)

(0.6 F)
(100 ohm)

]

x (TR − R@13.1)

MSP: Modified SASP (SASP plus Reset)
TR: Resistance at transducer
R@13.1: TR required to reach 13.1 k-ohm start level
DEMAND LIMIT (1-STAGE OR 2-STAGE) — Both of the
Demand Limit functions on the units rely on external switches
to initiate the reset functions. Contact closures by the BMS
can be used in place of these switches. Contacts must be
isolated and suitable for 115-vac pilot duty operation.
For Single-Step Demand Limit, emulate function of switch
SW with contact closure controlled by the BMS. Set potentiometer P4 manually at the unit control box. Alternatively,
potentiometer P4 might also be emulated by a variable resistance transducer, with the BMS now able to adjust the
amount of demand limit.
For 2-Step Demand Limit, install the accessory Demand
Limit Control Module (DLCM) according the instructions
on page 18. Replace switch functions Switch 1 and Switch
2 with contact closures controlled by the BMS (see Fig. 29).
Follow unit control configuration instructions in the Demand Limit section on page 18.
SUPPLY DUCT PRESSURE SET POINT ADJUSTMENT
— Supply duct pressure set point adjustment from a remote
BMS is possible when the unit has been equipped with a
factory-option VFD (variable frequency drive). There are two
methods available:
• Direct 4 to 20 mA signal
• DDC direct to the VFD
Direct 4 to 20 mA Signal — During normal unit operation,
the factory-installed VFD receives a 4 to 20 mA signal from
the Duct Pressure (DP) transducer which indicates current
supply duct pressure. The VFD then determines the appropriate fan speed (using its internal PID logic feature) and
adjusts its output to the supply fan motor to suit. It is possible to emulate this 4 to 20 mA control signal by the BMS,
which will transfer control of the VFD to the BMS.
NOTE: When providing a direct 4 to 20 mA signal to the
VFD from a BMS with DP logic, disable the PID (proportion integrated derivative calculation process) feature of the
VFD.
DDC Direct to the VFD — Several accessory interface boards
are available for the VFDs that permit direct communication
between the VFD and several BMS communication systems. Contact your Carrier representative for information on
selecting an appropriate accessory interface board and the
name of the local service office (for sale and installation of
the accessory boards).

UNIT SUPPLY AIR SET POINT ADJUSTMENT — The
minimum Supply Air Set Point (SASP) temperature is established by the setting at Potentiometer P1 on the unit display board (see Fig. 6). The control point can also be adjusted
upward by emulating the function of the accessory Space
Temperature Reset package. The BMS can be used to cause
this reset by adjusting the resistance value in a variable resistance transducer with a 4 to 20 mA or 2 to 10 vdc signal
generated by the BMS.
This emulation requires the following field-supplied parts:
• Variable resistance transducer (Kele RES-1 or equivalent,
range 0 to 1000 ohms)
• Series resistance with potentiometer, suitable for manual
adjustment to 12.5 to 13.0 k-ohms total resistance
Field Connections (see Fig. 30) — Connect fixed resistance
with manual potentiometer and variable resistance transducer in series.
Connect wiring to rooftop unit at:
Size 034-044: TB3-12 and TB3-15
Size 054-104: TB4-12 and TB4-15
20

EXTERNAL ALARM SIGNAL — The unit controls provide an external alarm status signal via a 115-vac output signal at the relay board J5, available at TB2-4 and TB2-5
(common). This signal can be forwarded to the BMS by adding a signal relay at the alarm output, placing its coil across
terminals TB2-4 and TB2-5 and using its contacts to control
a discrete input to the BMS (see Fig. 31).
The alarm signal output is energized when any of the diagnostic codes is tripped.
REMOTE ECONOMIZER CONTROL — Economizer control is tightly integrated into the unit’s capacity control algorithms and diagnostic routines. Consequently, control
modifications that interfere with this standard operating sequence are not recommended.
Economizer position is determined by the unit processor
board based on current outdoor air enthalpy status and cooling capacity demand. The economizer damper actuator is a
floating point device with an internal brake and spring return. Its position is determined by the sequencing of relays
EOR (Economizer Open Relay) and ECR (Economizer Close
Relay). The economizer’s current position is sensed by the
processor board through position feedback potentiometer P2.
Whenever the economizer position potentiometer signal
is not consistent with the processor board’s commanded position, a fault condition is determined by the processor board
and an alarm signal is initiated. The processor board also
attempts to return the economizer damper to its fully closed
position during this fault condition by energizing the ECR
relay.
Any attempt to effect an external control of the economizer actuator will lead to an alarm condition and an automatic response by the unit control to attempt to close the
dampers.

034-048: TB3
054-104: TB4
R

TRANSDUCER

BMS
CONTROL

(4 TO 20 MA
OR
2 TO 10 VDC
SIGNAL)

P
R

—
—

LEGEND
Manual Potentiometer
Fixed Resistor
Field Wiring

Fig. 30 — Remote SASP Wiring

TB2

5
LIGHT
R

RELAY

SIGNAL TO BMS

Smoke Control Modes — It is common practice to
use rooftop units for aid in building smoke control in the
event of a building fire. The available functions include: Fire
Shutdown, Pressurization, Evacuation, and Smoke Purge. These
functions are enhanced when multiple rooftop units are used
to zone a building.
Implementation of the various Smoke Control modes on
these units requires the installer to modify the unit wiring to
add contacts (via either manual switches or relays) that will
selectively interrupt and override standard factory control sequences. See Table 5.
FIRE SHUTDOWN MODE — Fire Shutdown mode terminates all unit operation (cooling, heating, supply fan and power
exhaust). This mode prevents recirculation of contaminated
air back into the space or the admission into the space of
unsuitable outside air.
PRESSURIZATION MODE — Pressurization mode is intended to keep smoke out of a zone. Factory-installed optional economizer is required for this function. Pressurization is accomplished by:
• opening the economizer (option)
• running the supply fan (optional inlet guide vanes open or
optional VFD (variable frequency drive) at normal duct
static pressure set point)
• closing the power exhaust dampers (if installed as option
or accessory)
• shutting off the power exhaust fans (if installed as option
or accessory)
This allows the space to be overpressurized relative to adjacent zones and prevents or slows entry of smoke into this
space from adjacent zones.

—

LEGEND
Resistor (Factory Installed)
Factory Wiring
Field Wiring

Fig. 31 — External Alarm Indication

EVACUATION MODE — Evacuation mode removes smoke
or undesirable air from interior spaces without reintroducing
unsuitable air. Factory-installed, optional economizer with
optional or accessory power exhaust are required for this function. Evacuation is accomplished by:
• turning supply fan off
• opening the economizer (option required for this function)
• running the exhaust fans (must be provided via option or
accessory)
• opening the exhaust dampers
SMOKE PURGE MODE — Smoke Purge mode removes
smoke from the interior spaces and replaces it with fresh outside air. Factory-option economizer with optional or accessory power exhaust are required for this function. Smoke purge
is accomplished by:
• turning supply fan on
• opening the economizer (option required for this function)
• running the exhaust fans (must be provided via option or
accessory)
• opening the exhaust dampers

INSTALLATION — To enable one or more of the possible
smoke control modes available with these units, determine
the switches required for the desired mode(s) from Table 6,
field-supply and install the appropriate switches and field wire
per Fig. 32. Switch functions are shown in Table 7.

Pressurization — At command from the field switches for
Pressurization mode (see Table 5):
1. Economizer dampers will open
2. The HIR function will energize, opening room terminals
to full-open (heating) positions.
3. Supply fan will run. (If equipped with IGV: control vanes
will open. If equipped with VFD: the VFD will control to
duct static set point or best available with all terminals
open.)
4. Power exhaust dampers (if equipped) will close.
5. Power exhaust fans (if equipped) will turn off.
Evacuation — At command from the field switches for Evacuation mode (see Table 5):
1. Supply fan will turn off.
2. Economizer dampers will open.
3. Exhaust fans will run at maximum capacity.
4. Exhaust dampers will open.
Smoke Purge — At command from the field switches for
Smoke Purge mode (see Table 5):
1. Economizer dampers will open.
2. The HIR function will energize, opening room terminals
to full-open (heating) positions.
3. Supply fan will run. (If equipped with IGV: Control vanes
will open. If equipped with VFD: the VFD will control to
duct static set point or best available with all terminals
open.)
4. Exhaust fans will run at maximum capacity.
5. Exhaust dampers will open.

Table 5 — Smoke Control Modes
FUNCTION
Supply Fan
IGV/VFD†
Economizer
Return Air
Damper
Exhaust
Fans
Exhaust
Damper

Fire
Shutdown
Off
—
Closed

MODE
PressurEvacuation*
ization
On
Off
Open/On
—
Open
Open

Smoke
Purge*
On
Open/On
Open

Open

Closed

Off

Closed

Open

LEGEND
IGV — Inlet Guide Vane
VAV — Variable Air Volume
VFD — Variable Frequency Drive
*Power exhaust option/accessory required for this mode.
†Applicable to VAV units with appropriate options.

CONFIGURATION — No set points required for Smoke Control modes. Modes are activated by energizing all switches
appropriate for each Smoke Control mode.
OPERATING SEQUENCE
Fire Shutdown — At command from the field switches (see
Table 5), all unit operation (cooling, heating, supply fan and
power exhaust) will terminate.

Table 6 — Smoke Control Switches Required for Each Mode
FIRE
SHUTDOWN

PRESSURIZATION

SW-1
SW-2

SW-1
SW-2
SW-4
SW-5
SW-6
SW-9A/B

EVACUATION
(Modulating Power
Exhaust)
SW-1
SW-2
SW-3
SW-5
SW-6
SW-7
SW-8

NOTE: All switches are shown in ‘‘as installed’’ (power OFF or deenergized) position. In these positions, none of these
modes will be activated; normal unit operation is permitted by the base unit controls. To initiate any mode, all switches listed
under this mode in the table must be energized, causing the depicted contact position to change from depicted positions to
energized positions. Switches may be manually or electrically operated.

SMOKE
PURGE
SW-1
SW-2
SW-3
SW-4
SW-9A/B

Table 7 — Switch Functions
SWITCH
NUMBER
SW-1
SW-2
SW-3
SW-4
SW-5
SW-6
SW-7
SW-8
SW-9A/B

BP
DPS
EOR
HIR
IFC
IGV
N.C.
N.O.
PEC
PED
OFC
VFD

—
—
—
—
—
—
—
—
—
—
—
—

CONFIGURATION

VOLTAGE

FUNCTION

N.C.
N.C.
N.O.
N.O.
N.C.
N.O.
N.O.
N.C.
A: N.O.
B: N.C.

115
115
24
115
115
115
24
24

Deenergize 115-v (OFC, Comp, IFC, Electric Heaters)
Deenergize TRAN7 (Process Board)
Energize EOR (Open Economizer Outside Air Dampers)
Energize IFC and CR-3 (IGV/VFD)
Isolate IFC and PEC for Separate Operation
Energize PEC (Power Exhaust)
Open PED at DPS
Block Auto-Close at DPS (Due to Low BP)

115 max

Signal Room Terminals to Open (HIR1)

LEGEND
Building Pressure
Differential Pressure Switch
Economizer Open Relay
Heat Interlock Relay
Indoor Fan Contactor
Inlet Guide Vane
Normally Closed
Normally Open
Power Exhaust Contactor
Power Exhaust Damper
Outdoor Fan Contactor
Variable Frequency Drive

The inlet guide vanes are controlled by a differential pressure switch (DPS). On sizes 034-048, the DPS is located in
the auxiliary control box at the economizer end of the unit
(see Fig. 33). On sizes 054-104, the DPS is located in the
supply fan section. See Fig. 34. Use a nominal 3⁄8-in. plastic
tubing.
VARIABLE FREQUENCY DRIVE — The tubing for the
duct pressure (DP) control option should sample supply duct
pressure about 2⁄3 of the way out from the unit in the main
trunk duct, at a location where a constant duct pressure is
desired.
The duct pressure is sensed by a pressure transducer. The
pressure transducer output is directed to the VFD. On 034048 units the DP transducer is located in the auxiliary control box. On 054-104 units, the DP transducer is located in
the supply fan section. See Fig. 34. Use a nominal 1⁄4-in.
plastic tubing.

Air Pressure Tubing — Before options such as inlet
guide vanes (IGV), variable frequency drive (VFD), and/or
modulating power exhaust can operate properly, the pneumatic tubing for pressure sensing must be installed. Use fireretardent plenum tubing (field-supplied). Tubing size depends
on type of control device (see Table 8 below). Tubing must
be run from the appropriate sensing location (in the duct or
in the building space) to the control device location in the
unit.
Table 8 — Tubing Size
OPTION

UNITS

Inlet Guide Vanes (IGV)
ALL
Variable Frequency
ALL
Drive (VFD)
Modulating Power Exhaust FK,FKX,JK,JKX

NOMINAL TUBE
SIZE (in.)
3⁄8
⁄

⁄

INLET GUIDE VANES — The tubing for the duct pressure
(DP) control option should sample supply duct pressure about
2⁄3 of the way out from the unit in the main trunk duct, at a
location where a constant duct pressure is desired.

054-104 UNITS

034-048 UNITS
TB2

SW-1

TB2

SW-1

REMOVE JUMPER
TB2

SW-2

REMOVE JUMPER

TB2

SW-2

SW-3

1
SW-4

TB2
5

TB2

SW-5

REMOVE JUMPER

TB3

TB4

TB2

SW-3

SW-6

5
SW-9A

TB3
3
HIR

TB3
3

SW-9B
5

SW-4

SW-5

TB2

REMOVE JUMPER

TB2

TB3

TB4

TB2

SW-6

1
SW-9A

TB4
4

TB3

TB4

HIR
4

SW-9B
5

REMOVED FROM TB4-7

SW-7

ALL UNITS

DPS
SW-8
WHT

VIO
NO

REMOVED
FROM C-DPS

GRA

LEGEND
—
—
—
—

TB2

REMOVED FROM TB3-7

DPS
HIR
SW
TB

TB4
5

REMOVE JUMPER

TB2

TB2
8

REMOVE JUMPER

TB3

TB2

Differential Pressure Switch
Heat Interlock Relay
Switch
Terminal Block

Fig. 32 — Smoke Control Wiring

TB4
7

MODULATING POWER EXHAUST — The tubing for the
building pressure control (achieved via the Modulating Power
Exhaust option) should sample building pressure in the area
near the entrance lobby (or other appropriate and sensitive
location) so that location is controlled as closely to design
pressures as possible.
A differential pressure switch (DPS) is used to control the
actuator on the modulating discharge damper in exhaust fan
no. 1. The building pressure (BP) DPS is located in the auxiliary control box of the unit. See Fig. 33 and 35. Use a nominal 3⁄8-in. plastic tubing.
For instructions on adjusting BP control set points, refer
to Start-Up, Modulating Power Exhaust section in this book.

START-UP
Fig. 33 — Modulating Power Exhaust and Inlet
Guide Vane Differential Pressure Switch
(Sizes 034-048)

Initial Check
IMPORTANT: Do not attempt to start unit, even momentarily, until all items on the Controls Start-Up Checklist (in installation instructions) and the following steps
have been completed.
1. Verify unit has been installed per the Installation Instructions included in the unit installation packet.
2. Verify that all auxiliary components (sensors, controls,
etc.) have been installed and wired to the unit control boxes
per these instructions, the unit Installation Instructions,
and the unit wiring label diagrams.
3. Verify that air pressure hoses (static, duct, etc.) are properly attached, routed, and free from pinches or crimps that
may affect proper control operation.
4. Set any control configurations that are required (fieldinstalled accessories, etc.). The unit is factory configured
for all appropriate factory-installed options with the applicable controls programmed to the default values.
5. Check and adjust unit set points. See Table 9.
6. Check tightness of all electrical connections.
7. Perform quick test (see Quick Test Program section on
page 31).

Fig. 34 — Inlet Guide Vane Differential
Pressure Switch and Variable Frequency Drive
Duct Pressure Transducer (Sizes 054-104)

Fig. 35 — Modulating Power Exhaust Differential
Pressure Switch (Sizes 054-104)

Table 9 — Potentiometer Inputs and Ranges
POTENTIOMETER

CONTROL
VALID
RANGE

DESCRIPTION

LOCATION

Supply Air
Set Point
Economizer
Position

45 to 70 F

DEFAULT VALUE

Reset Limit

Display
Board
Economizer
Motor
Accessory
Board

P4†

Demand Limit,
Single-Step

Main Control Box

0 to 100%

None

DLCM-P1
DLCM-P2

Demand Limit,
2-Step

DLCM Board
DLCM Board

50 to 100%
0 to 49%

None
None

P5*

Minimum Economizer
Position

Accessory Board

0 to 100%

None

Warm-Up
Set Point

Accessory Board

40 to 80 F

40 F if 0° F < P6 < 40 F OR IF P6 < 95 F
OR IF P6 < 0
80 F if 80 F < P6 < 95 F

Reset
Temperature

Reset Board

40 to 100 F

None

P1
P2*

P7**

45 F if -22 F < P1 < 45 F
70 F if P1 > 70 F OR IF P1 < -22 F

0 to 100%

None (0 if P2 is bad)

0 to 80 F

None (limited to 70 F maximum)

*Optional factory-installed economizer is required. Potentiometer P2 is not a set point.
†Accessory two-step demand limit module is required (which has 2 potentiometers), or a 5 to 20 k-ohm
field-supplied potentiometer is required for single-step demand limit.
**Accessory temperature reset is required.
NOTE: Potentiometers P1-P6 input data to pin terminal connector J3.
Potentiometer P7 inputs data to pin terminal connector J1.

Table 11 — Configuration Header Jumpers

Configuration Header — The configuration header
is a series of 8 small wires that are broken (open circuit) or
unbroken (closed circuit) in a pattern to indicate several unique
characteristics of the unit. The configuration header is factory set and should not be changed; changing the factory setting may cause the unit to malfunction.
Before start-up, visually check the configuration header
against the factory setting for the unit size. See Table 10 for
factory settings. See Table 11 for purpose for each jumper.

JUMPER
NUMBER
1,2
3,4,5
6
7
8

TXV
VAV
▫
n

Table 10 — Configuration Header and
DIP Switch Factory Settings
JUMPER OR
SWITCH NO.
1
2
3
4
5
6
7
8

UNIT SIZES
UNIT SIZE
UNIT SIZE
034-038,
044
104
048-088
Header Switch Header Switch Header Switch
Position Position Position Position Position Position
▫
Off
▫
Off
▫
Off
n
Off
n
Off
n
Off
n
On/Off*
n
On/Off*
n
On/Off*
▫
On/Off*
▫
On/Off*
n
On/Off*
▫
Off
▫
Off
▫
Off
n
Off
n
On
n
On
▫
On
▫
Off
▫
Off
n
Off
n
Off
n
Off

—
—
—
—

FUNCTION
Unit Type
Qty Compressors
Expansion Valve
Power Frequency
Not Used

FACTORY
SETTING
▫ n
n ▫ ▫
n
▫
n

MEANING
VAV Rooftop Unit
2 Compressors
TXV
60 Hz
No Significance

LEGEND
Thermostatic Expansion Valve
Variable-Air Volume
Broken Jumper (open circuit)
Unbroken Jumper (closed circuit)

DIP Switches — The DIP switches configure the unit
for several factory-installed options and field-installed accessories, plus factory unloaders. The DIP switches are located under a plastic enclosure which must be removed for
access. See Fig. 1. The switches can be field adjusted. Switches
must only be adjusted when control power is deenergized.
See Table 12 for DIP switch purposes and Table 10 for factory settings of the switch positions.

Disconnect control power before changing the settings
of the DIP switches. To disconnect control power, open
the control circuit breaker.

LEGEND
DIP — Dual, In-Line Package
▫
— Broken Jumper (open circuit)
n
— Unbroken Jumper (closed circuit)
*Depending on factory-installed options or field-installed accessories.

Potentiometer inputs and ranges are summarized in
Table 9. Information on individual set point potentiometers
(including function, location and range data) are shown
below:
SUPPLY AIR SET POINT (Leaving-Air Temperature) (P1)
— This potentiometer establishes the set point for cooling
cycle operation of the VAV unit. The VAV control uses a
valid control range of 45 to 70 F, and the potentiometer has
a valid range of −22 to 70 F. If the set point is between −22
and 45 F, the control will use a value of 45 F. If the set point
is outside the valid range (less than −22 F or greater than
70 F), an alarm condition will be signaled and a default value
of 70 F will be used.
ECONOMIZER MINIMUM POSITION (P5) — This potentiometer specifies the minimum opening position for the
optional economizer during running periods. It has both a
valid range and an operational range of 0 to 100%.
SASP RESET TEMPERATURE (P7) — This potentiometer
establishes the space temperature at which the control will
initiate the reset of the SASP (i.e., the unit control begins to
raise the base SASP, to prevent overcooling of the space).
The potentiometer has a valid range of 40 to 100 F. Refer to
Space Temperature Reset section on page 16 for further discussion of SASP Reset operation.
RESET LIMIT (P3) — Used in conjunction with P7 potentiometer, this potentiometer establishes the maximum temperature for the modified SASP value during the Reset function. This potentiometer has a valid range of 0° to 80 F.
DEMAND LIMIT, SINGLE-STEP (P4) — This potentiometer establishes the maximum amount of compressor capacity permitted by the unit control when single-step demand
limit operation is implemented (by closing contact set to potentiometer wiper arm). This potentiometer is field-supplied
and -installed and will be located in the main control box.
The valid range is 0% to 100%, which is also the operational
range.
If the wiper arm is open, all capacity stages can be used.
When the wiper arm is closed, the capacity is reduced by the
amount set on potentiometer P4.
DEMAND LIMIT, 2-STEP — The accessory 2-step
demand limit control is a 2-potentiometer system. The
demand limit control board (DLCM) accessory board is
field-installed in the main control box; the 2 control potentiometers are located on the DLCM. Potentiometer DLCM-P1
establishes the maximum amount of compressor capacity available when SW1 is closed and has a valid range is 50% to
100%. Potentiometer DLCM-P2 establishes the maximum
amount of compressor capacity available when SW2 is closed
and has a valid range is 0% to 49%.
If no power is supplied to the DLCM, all capacity stages
can be used. When power is supplied to terminal IN1 only,
the first step of demand limit control is energized and the
capacity is reduced by the amount set on potentiometer P1.
When power is supplied to IN2 (or IN1 and IN2), the capacity is reduced by the amount set on potentiometer P2.
MORNING WARM-UP (P6) — This potentiometer establishes the set point temperature for the Morning Warm-Up
function. This is the temperature at which the morning warm-up
sequence is terminated and VAV cooling operation begins.
The valid control range is 0° to 95 F, but the control is programmed to accept a range of 40 to 80 F. If the set point is
between 0° and 40 F, the control will use a value of 40 F.
If the set point is between 80 and 95 F, the control will use
a value of 80 F. If the set point is outside the valid range
(less than 0° F or greater than 95 F, an alarm condition will
be signaled and a default value of 40 F will be used.

DIP SWITCH NO. 1 — Supply Air Set Point (SASP) Reset
Type. Factory setting is OFF. Do not change.
DIP SWITCH NO. 2 — SASP Reset Enabled. Factory setting is OFF (no SASP reset enabled). If SASP reset has been
installed, enable it by changing switch position to ON.
DIP SWITCH NO. 3 — Economizer option. If economizer
option has been installed, this switch will be ON. If there is
no economizer installed, this switch will be OFF. Confirm
setting per Table 10. Change only if in error.
DIP SWITCH NO. 4 — Morning Warm-Up. For 48FK,JK
models, this switch will be ON (morning warm-up enabled).
For 50FK,JK units with factory-installed electric heaters, this
switch will be ON. For all other units, this switch will be
OFF. If accessory electric heaters are installed (for 50FK,JK
without plenum option), change this switch to ON.
DIP SWITCH NO. 5 — Demand Limit. Factory setting is
OFF (demand limit not enabled). If Demand Limit (singlestep or 2-step accessory) has been installed, change this switch
to ON.
DIP SWITCHES NO. 6 AND NO. 7 — Unloader Configuration. These are factory set to match unit size. Confirm settings per Table 12. Change only if in error.
Table 12 — DIP Switches
SWITCH
NO.
1
2
3

FUNCTION
Reset
Mode
Reset
Select
Economizer

Morning
Warm-Up
Demand
Limit

6,7

Unloaders

Not Used

SWITCH
POSITION*
Off
On
Off
On
Off
On
Off
On
Off
Off, Off
On, Off
Off, On
Off

MEANING
Space or Outdoor-Air Reset
(DO NOT CHANGE)
Reset Used
Reset Not Used
Enable Economizer
Disable Economizer†
Enable Morning Warm-Up**
Disable Morning Warm-Up**
Enable Demand Limit
Disable Demand Limit
No Unloaders
1 Unloader
2 Unloaders
No Significance

LEGEND
DIP — Dual, In-Line Package
*Control circuit breaker must be off before changing the setting of the DIP switch.
†No economizer.
**And/or electric heat (50FK,JK units without plenum only).

Adjusting Set Points — Set points for unit operation
are established via potentiometer settings. Set points for Supply Fan controls are set at the VFD keypad (if installed) or
at the IGV differential pressure switch (DPS1) (if IGV option installed). Set points for modulating power exhaust (option or accessory) are set at the differential pressure switch
(DPS2).
Potentiometers — All of the set point potentiometers
must be set before the unit is started in order for the unit to
function properly. Each of the potentiometers has a valid range
that is used by the control. The valid range is defined as the
potentiometer’s resistance value that the control will not consider to be in error. This is usually between 10% and 90%
of the potentiometer’s total resistance. The control has been
programmed to accept an operational range for the potentiometer, which may not be the same as the valid range.

Supply Fan Control with IGV Option — The inlet
guide vane option will modulate the supply fan airflow in
order to maintain the static pressure in the supply duct. The
set point for duct static pressure is established at the differential pressure switch for the IGV control.
SIZE 034-048 UNITS — The inlet guide vane differential
pressure switch is located in the auxiliary control box mounted
in the corner under the side air hood that is next to the access
door marked FILTER SECTION. To gain access to this control box, remove the auxiliary control box cover. When
replacing cover, be sure to properly secure it in order to
prevent water from being drawn into the unit. See Fig. 36
and 37.
SIZE 054-104 UNITS — The inlet guide vane differential
pressure witch is mounted on an upright located behind the
supply-fan motor. See Fig. 36-38.
The IGV differential pressure switch has an adjustable
set point range of 1.1 to 3.5 in. wg. and a factory setting of
1.9 in. wg.
To adjust set point, turn set point adjusting screw (see
Fig. 39) clockwise to decrease set point and counterclockwise to increase set point. This switch also has an adjustable
null span. The null span is the pressure change that can be
made without contacts opening or closing. It is adjustable
from 0.06 in. wg to 0.17 in. wg when set point is at minimum position (1.1 in. wg) and 0.11 in. wg to 0.31 in. wg
when set point is at maximum position (3.5 in. wg). To adjust null span, turn a null adjusting screw (Fig. 39) clockwise to decrease span and counterclockwise to increase span.
All switches leave factory with null span set at maximum
position. The smaller the null span, the closer the pressure
will be maintained to desired set point.

*The inlet guide vane differential pressure switch for the 034-048 units
is located in the back of the unit in the auxiliary control box. Its location is not shown in this figure.

Fig. 36 — Inlet Guide Vane Motor,
50FK,JK034-074 Units

Supply Fan Control with VFD Option — The VFD
option will modulate Supply Fan motor (and thus wheel) speed
to maintain the static pressure in the ductwork. Set point for
the VFD option is set at the VFD, using the display keyboard on the front of the VFD enclosure. See Fig. 40.
NOTE: The VFD will always provide the proper phase
sequence to the supply-fan motor. The supply-fan motor operates in proper rotation regardless of the phase sequence to
the unit. If, upon start-up, the outdoor fans operate backwards but the supply fan operates in the correct direction,
reverse any two leads to the main terminal block. All fans
will then operate in the correct direction.
To set the duct static pressure, perform the following steps.
The factory setting is 2.5 in. wg. The duct transducer has
a range from 0 to 5 in. wg. The transducer output is 4 to
20 mA, therefore, 0 to 5 in. wg is proportional to the 4 to
20 mA and must be expressed to the VFD in terms of percentage of the frequency range. Refer to Table 13. The set
point value is a percentage of the maximum output frequency. Locate the duct static pressure closest to that desired and use the corresponding set point value. If necessary,
interpolation between duct static pressures is permissible.

*The inlet guide vane differential pressure switch for the 034-048 units
is located in the back of the unit in the auxiliary control box. Its location is not shown in this figure.

Fig. 37 — Inlet Guide Vane Motor, 48FK,JK, 50FY,JY,
and 50FJX,FJY,FKX,FKY034-074 Units

Factory-installed optional VFD is located near the supply fan and motor. During any service work or programming at the VFD, operation of the fan and motor
is not desirable and may be dangerous. Either disable
the unit supply fan (following instructions below) or install the accessory VFD remote display accessory.
Fig. 38 — Inlet Guide Vane Motor,
Size 078-104 Units

ADJUST VFD SET POINT — To adjust the VFD set point,
the VFD must be powered; however, since it is located near
the supply fan and motor, operation of the fan and motor is
not desirable. Either disable the Supply Fan or install the
accessory VFD remote display accessory.
DISABLE SUPPLY FAN MOTOR — To disable the supply
fan motor and change programming of VFD set point:
1. Turn off Indoor Fan Circuit Breaker (IFCB). This will
remove power to the VFD.
2. Wait for the VFD display to go blank and remove VFD
cover without touching any interior components.
3. Ensure that the charge indicator lamp is out which indicates that the VFD is discharged. The lamp is located
on the upper right hand corner of the terminal block. If
still lit, wait until lamp goes completely out. This may
take several minutes.
4. Remove jumper from terminals ST-CC (see Fig. 41) and
replace VFD cover.
5. Turn on IFCB.
6. The drive output will now be disabled but the programming can be changed.
7. Change VFD set point according to Table 14 shown
below.
8. Once the program changes are completed, turn off IFCB.
9. Wait for the VFD display to go blank and remove VFD
cover without touching any interior components.
10. Ensure that the charge indicator lamp is out which indicates that the VFD is discharged. The lamp is located
on the upper right hand corner of the terminal block. If
still lit, wait until lamp goes completely out. This may
take several minutes.
11. Replace jumper to terminals ST-CC.
12. Replace VFD cover.
13. Turn on IFCB to enable the drive.
For additional information on the VFD (including basic
troubleshooting, factory jumper arrangements, and Carrier
factory defaults programming), refer to Troubleshooting, Variable Frequency Drive section (page 52).

CAPACITOR

NULL
ADJUSTMENT

COM
N.C.
N.O.

NULL DECREASE
SET POINT
DECREASE

SET
POINT
ADJUSTMENT

PLA

SET
POINT
INDICATOR

LEGEND
COM — Common
N.C. — Normally Closed
N.O. — Normally Open

Fig. 39 — Differential Pressure Switch for Inlet Guide
Vane and Static Pressure Control Option and
Modulating Power Exhaust Option

HZ
PERCENT
SECONDS
KW/AMPS/VOLTS

SETUP
PROGRAM
MONITOR

RUN

READ
WRITE

STOP
RESET

LOCAL/REMOTE

MANUAL/AUTO

SPEED CTRL

RUN MODE

IMPORTANT: The Carrier factory default values for
the VFD may be different than the default values of
the manufacturer. Refer to the Service section when
checking default values.

Fig. 40 — Variable Frequency Drive Keypad
DETERMINE VFD SET POINT — The unit of measure for
the Duct Pressure set point at the VFD is output frequency
(Hz), representing the desired DP set point (DPSP) in inches
of water gage (in. wg). To convert desired DPSP into the
VFD set point, refer to Table 13. Locate the pressure value
in the table closest to the desired DPSP for this installation
and use the corresponding VFD set point (Hz) value. If necessary, interpolation between duct static pressure values is
permissible.

P24 RES RR
ST

FM AM CC

S1
CC

S2
RX

S4 RCH P24 LOW LOW
IV

FP FLC FLB FLA

REMOVE
JUMPER

Fig. 41 — Jumper Removal to Disable Motor

Table 13 — VFD Set Point (Frequency Command) for Duct Pressure
PRESSURE
(in. wg)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75

VFD SET POINT (Hz)
0
3
6
9
12
15
18
21

CONTROL SIGNAL
(mA)
4.0
4.8
5.6
6.4
7.2
8.0
8.8
9.6

PRESSURE
(in. wg)
2.00
2.25
2.50
2.75
3.00
3.25
3.50

VFD SET POINT
(Hz)
24
27
30
33
36
39
42

CONTROL SIGNAL
(mA)
10.4
11.2
12.0
12.8
13.6
14.4
15.2

Table 14 — Changing the VFD Set Point (Frequency Command)*
KEY OPERATION

LED MESSAGE
XX.X or OFF

↓
↓↑
R/W

60.0
45.0 (flashing)
FC and 45.0 (flashing)
XX.X or OFF

EXPLANATION
Standard Monitor Mode (output frequency). If drive is disabled, display
will read 9OFF9. If enabled, display will show current output frequency
Pressing arrow key once will display the current frequency setpoint
Pressing up/down arrow keys changes the desired setpoint
When R/W is pressed, the parameter name (FC) and the new value
(45.0) will alternately flash to indicate that the new value has been
stored. After 2 cycles, the display will return to the standard monitor
mode.
Standard Monitor Mode (output frequency). If drive is disabled, display
will read 9OFF9. If enabled, display will show current output frequency

*Choose set point from Table 13 according to desired duct pressure.

DIFFERENTIAL PRESSURE SWITCH — The modulating
power exhaust DPS has a set point range of 0.5 in. wg to
−0.5 in. wg. Factory setting is +0.1 in. wg. To adjust set point,
turn set point adjusting screw (see Fig. 39) clockwise to
decrease set point and counterclockwise to increase set point.
This switch also has an adjustable null span. The null span
is the pressure change that can be made without contacts
opening or closing. It is adjustable from 0.06 in. wg to
0.14 in. wg when set point is at minimum position
(−0.5 in. wg) and 0.07 in. wg to 0.14 in. wg when set point
is at maximum position (+0.5 in. wg). To adjust null span,
turn null adjusting screw (Fig. 39) clockwise to decrease span
and counterclockwise to increase span. All switches leave
factory with null span set at maximum position. The smaller
the null span, the closer the pressure will be maintained to
desired set point.

Modulating Power Exhaust (Option or Accessory) — The Modulating Power Exhaust system will maintain space pressure by modulating power exhaust fan no. 1
and staging power exhaust fan no. 2. Building pressure set
point is established at the modulating power exhaust differential pressure switch (DPS).
SIZE 034-048 UNITS — The modulating power exhaust differential pressure switch is located in the auxiliary control
box mounted in the corner next to the power exhaust motor
door. To gain access to this control box, remove the auxiliary control box cover. When replacing cover, be sure to properly secure it in order to prevent water from being drawn
into the unit. See Fig. 33.
SIZE 054-104 UNITS — The modulating power exhaust differential pressure switch is mounted below the auxiliary control box next to the access door labeled FILTER SECTION.
See Fig. 35.

For each step of the 33-step program, display button must
be pressed twice. On first press, step number is displayed;
second press initiates required action and appropriate code
is displayed.
NOTE: The step number is a numeral followed by a decimal
point (a 2-digit number has a decimal point after each numeral). The action code number is one or 2 digits with no
decimal point(s).

START UNIT
To start unit:
1. Close the unit-mounted ON/OFF switch (located in the
main control box).
2. Close the field-supplied and -installed timeclock (or control) switch (contacts located at Terminals 1 and 2 (TB3
for 034-048, TB4 for 054-104).
IMPORTANT: The field-supplied and installed switch
(or timeclock) MUST BE CLOSED to put unit in
Occupied mode. Unit WILL NOT START until this
is accomplished.

IMPORTANT: Once quick test is initiated, display button must be pressed at least once every 10 minutes for
control to remain in quick test mode. If button is not
pressed within this time, control will attempt to start
the unit.

3. Initialization mode begins (see Operating Information section on page 34 for complete description of sequences
and display codes).
4. Run Quick Test. If the display button is pressed during
the initialization mode period, the unit will run its selfdiagnostic routine. When this is in effect, an 88 will appear in the display screen. Refer to Quick Test Program
section below, for instructions on completing the Quick
Test program.

To recheck any step in quick test program, control must
be recycled by turning unit control switch off for a few seconds, and then turning it back on again. Restart quick test
program as described above and proceed through quick test
steps. Press display button twice for each step until step to
be rechecked is reached.
The quick test program is divided into 3 sections as described below and shown in Tables 15-17.
1. Quick Test Steps 1.-1.3. — Unit Configuration and Switch
Check
The microprocessor in unit control system is programmed
by 2 switch assemblies located on processor board
(Fig. 1). The configuration header is factory set and cannot be changed in the field. The DIP switch assembly contains 8 microswitches that must be set in accordance with
the various options selected by the customer. All DIP
switches should be checked and set to proper position for
options selected prior to the quick test. See Configuration
of Header and DIP Switch Assembly section on page 5
for factory switch settings. The DIP switch functions and
display codes are shown in Table 15.
2. Quick Test Steps 1.4.-2.3. — Thermistor and Set Point
Potentiometer Check
In these steps, the microprocessor checks resistance values of all sensors and set point potentiometers to ensure
that they are functional, connected properly, and set within
proper range for unit configuration.
Nominal resistance values for all sensors range from 363,000
to 219 ohms in accordance with Table 18. Normal display code for good sensors and potentiometers is 1. A display code of 0 indicates a faulty potentiometer, thermistor
or wiring. A 0 display also indicates that option is not
being used.
Table 16 shows thermistor and set point potentiometer
functions and quick test display codes.

Quick Test Program — Turn on power to unit.
IMPORTANT: The field-supplied switch (or timeclock) must be closed to put unit into the occupied mode.
The quick test program utilizes the 2-digit LED display
(see Fig. 6) on the set point board to show status of all input
and output signals to microprocessor. Display action and quick
test procedures are described below.
The quick test program is a 33-step program that provides
a means of checking all input and output signals of controls
prior to unit start-up. This check ensures that all control options, thermistors, and control switches are in proper working order.
When unit control circuit is switched to Occupied mode,
a 20 will appear on the display. Immediately press display
button once. An 88 will appear on the display and alarm
light on display board will be energized. This indicates that
control system is ready to run quick test program.
IMPORTANT: Do not allow unit control circuit to
remain energized with 20 showing on display for more
than 2 minutes. If display button is not pressed within
this time period, control will attempt to start unit.

Table 15 — Quick Test, Unit Configuration and Switch Check
QUICK
TEST
STEP NO.

NORMAL
DISPLAY

Type Unit — Air-Cooled VAV

Configuration Header

No. of Compressors

Configuration Header

No. of Unloaders
(034,038,048-088)

DIP Switch No. 6 and 7

2
1

(044, 104)

60-Hertz Power

Configuration Header

0 or 1

0 — No Reset (Switch Off)
1 — Reset On (Switch On)

DIP Switch No. 2

0 or 1

0 — No Economizer (Switch Off)
1 — Economizer On (Switch On)

DIP Switch No. 3

0 or 1

0 — No Warm-Up (Switch Off)
1 — Warm-Up Used (Switch On)

DIP Switch No. 4

0 or 1

0 — Demand Limit Not Used
(Switch Off)
1 — Demand Limit Used
(Switch On)

DIP Switch No. 5

0 or 1

0 — Enthalpy Switch Open
1 — Enthalpy Switch Closed

1.0.

1 — Low-Pressure Switch Closed

Low-Pressure Switch 1

1.1.

1 — Low-Pressure Switch Closed

Low-Pressure Switch 2

1.2.

No Circuit 1 Oil Pressure Switch

None*

1.3.

No Circuit 2 Oil Pressure Switch

None*

DESCRIPTION

LEGEND
DIP — Dual, In-Line Package
EC — Enthlapy Control
VAV — Variable Air Volume
*Units are not equipped with oil pressure switches.

CONTROL SWITCH

Table 16 — Quick Test, Thermistor and Potentiometer Check
QUICK
TEST
STEP NO.

NORMAL
DISPLAY

1.4.

1 — Thermistor OK
0 — Thermistor Faulty

Supply Air
Thermistor (T1)

1.5.

1 — Thermistor OK
0 — Thermistor Faulty

Return Air
Thermistor (T2)

1.6.

1 — Thermistor OK
0 — Thermistor Faulty

Circuit 1 Condenser Thermistor
(T3)

1.7.

1 — Thermistor OK
0 — Thermistor Faulty

Circuit 2 Condenser Thermistor
(T4)

1.8.

1 — Thermistor or Potentiometer OK
0 — Thermistor or Potentiometer Faulty or
Option not used

Accessory Space Temperature Thermistor (T10)
or Accessory Reset Potentiometer (P7)

1.9.

1 — Potentiometer OK
0 — Potentiometer Faulty

Supply-Air Set Point
Potentiometer (P1)

2.0.

1 — Potentiometer OK
0 — Potentiometer Faulty or Option not used

Accessory Reset Limit
Potentiometer (P3)

2.1.

1 — Potentiometer OK
0 — Potentiometer Faulty or Option not used

Accessory Demand Limit
Potentiometer (P4)

2.2.

1 — Potentiometer OK
0 — Potentiometer Faulty or Option not used

Minimum Position
Economizer
Potentiometer (P5)

2.3.

1 — Potentiometer OK
0 — Potentiometer Faulty or Option not used

Warm-Up Set Point
Potentiometer (P6)

THERMISTOR OR
POTENTIOMETER*

DESCRIPTION

*Potentiometer P2 is not listed since it is not part of the quick test. If on unit start-up a Code 83 is displayed, check potentiometer P2.

Table 17 — Quick Test, Output Relay Check
QUICK
TEST
STEP NO.

NORMAL
DISPLAY

DESCRIPTION

RELAY NUMBER

2.4.

1 — Open Economizer or Open Relay if no Economizer

2.5.

1 — Close Economizer or Close Relay if no Economizer

2.6.

1 — Energize Fan Relay and Heat Relay

2.7.

Energize Stage 1 Condenser Fan(s)

K11

2.8.

Energize Stage 2 Condenser Fan(s)

K12

2.9.

0 then 1 then 0

Energize Compressor 1†

3.0.

Energize Unloader 2; Not Used (044, 104)

3.1.

Energize Unloader 1

3.2.

0 then 1 then 0

Energize Compressor 2†

3.3.

Not Used

LEGEND
CR — Control Relay
*K9 (fan relay) will remain on for duration of quick test.
†Compressor will be energized for 10 seconds. Zero indicates open CR; 1 indicates closed CR.

K9* and K10

Table 18 — Sensor Resistance Values
TEMP
(F)
−60
−55
−50
−45
−40
−35
−30
−25
−20
−15
−10
−5
0
5
10
15
20
25
30
35
40

RESISTANCE
(Ohms)
362,640
297,140
245,245
202,841
168,250
139,960
116,820
98,420
82,665
69,685
58,915
50,284
42,765
36,475
31,216
26,786
23,164
19,978
17,276
14,980
13,085

TEMP
(F)
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145

RESISTANCE
(Ohms)
11,396
9,950
8,709
7,642
6,749
5,944
5,249
4,644
4,134
3,671
3,265
2,913
2,600
2,336
2,092
1,879
1,689
1,527
1,377
1,244
1,126

TEMP
(F)
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
230
235
240

load if the outdoor enthalpy is good. As long as the outdoorair enthalpy is acceptable, no mechanical cooling will take
place until the economizer dampers are fully open. The rest
of the steps and the operational sequence vary due to the
number of compressors and unloaders. Refer to Operating
Sequence section on page 35 for the unit stages of operation.
CODES 20 THROUGH 30 AND 88, OPERATIONAL STATUS — These codes indicate special operational modes, such
as initialization, morning warm-up, temperature reset, demand limit, or an internal failure of the board. Codes 23-25
and 27-29 are not used on these units.
Initialization — When the control is turned on, the display
shows a 20 for approximately 2 minutes to indicate that the
control is in the initialization mode. During this time, the
economizer dampers open and close to determine the resistance range of the economizer position potentiometer (P2)
for full economizer operation. The processor loads the necessary constants for proper unit operation and checks the thermistors and other potentiometers for their values and validity. After the initialization period, the display screen goes
blank until the display button is pressed. If the display button is pressed during the 2-minute initialization period, the
control goes into the Quick Test mode.
Temperature Reset — If the unit is equipped with the accessory temperature reset package, and DIP switch 2 is in
the ON position, the unit will reset the supply-air temperature to a calculated value when necessary. When this condition is in effect, a 21 will appear in the display.
Demand Limit — If the unit is equipped with the accessory
demand limit control module or the field-supplied, singlestep demand limit potentiometer, and DIP switch 5 is in the
ON position, the unit will limit the capacity stages to a predetermined value. When this condition is in effect, a 22 will
appear in the display.
Morning Warm-Up —If the morning warm-up heat routine
is enabled using DIP switch 4, and conditions of the occupied space warrant, the unit will begin the morning warm-up
routine. When this condition is in effect, a 26 will appear
in the display.
Internal Failure — If the unit detects an internal fault (such
as a time measurement failure), or detects an incorrect voltage on an input channel, a 30 will be displayed, and the
unit will shut down.
Quick Test — If the display button is pressed during the
initialization period of the processor, the unit will run its selfdiagnostic routine. When this is in effect, an 88 will appear
in the display screen.
CODES 51 THROUGH 87, DIAGNOSTIC INFORMATION — These codes indicate diagnostic information when
there is a unit problem such as a faulty thermistor, potentiometer, or compressor fault. Refer to Diagnostic Codes section on page 45 for more details. Codes 53, 54, 57, 58, 61,
62, 65-69, 73, 74, and 77-80 are not used on these units.
Under normal operation, only the stage number is displayed when the display button is pressed. If a status or overload code is displayed, the display will rotate every 2 seconds and will display up to 3 codes. Overload information
takes priority over all other codes. The codes are stored in
the microprocessor as long as the board remains energized.

RESISTANCE
(Ohms)
1,020
929
844
768
699
640
585
535
490
449
414
380
350
323
299
276
255
236
219

3. Quick Test Steps 2.4.-3.3. — Output Relay Check
These quick test steps allow microprocessor to check
output signals from relay boards in unit control system. In addition, operation of all the condenser fans, compressors, and economizer (if equipped) are checked at each step.
Normal display for Steps 2.4. through 2.8. is 1. In Steps
2.9. through 3.2., each compressor and unloader is started
and allowed to run for approximately 10 seconds. At startup, a 0 will appear on the display followed by a 1 (Steps
2.9. and 3.2.) in a few seconds. Steps 3.0. and 3.1. will
always be 0 since there are unloaders, and Step 3.3. will
always be zero since it is not used.
At end of the 10-second time period, a 0 will return to the
display board indicating that test step has been successfully completed (Steps 2.9. and 3.2.). The 1 indicates that
was tested.
Fan and compressor operating sequence for quick test
Steps 2.4. through 3.3. are shown in Table 17.
If the quick test steps do not operate as described above,
a defect exists in one or more of the following: relay being
tested, electronic control, or unit wiring. Determine problem
and correct.

OPERATING INFORMATION
Digital Display — The VAV control system uses a 2-digit
LED display located on the display board to display operational information and diagnostic codes.
CODES 0 THROUGH 8, CAPACITY STEPS — These codes
indicate the number of cooling stages active at the time the
display button is pressed. The highest code indicated on the
display will be 6 for the 034,038 and 048-088 units, 4 for the
044 units, and 8 for the 104 units.
Capacity steps are directly related to pin terminal connector J6 output. At step zero, the unit has no mechanical cooling on, and the economizer may or may not be operating
(depending on the outdoor air conditions). Once a cooling
load is detected (T1 thermistor reads above the supply-air
set point), the economizer will begin modulating to meet the

Compressors, unloaders, and condenser fans will be cycled
to maintain a supply-air temperature 2° F below the potentiometer P1 set point once the mechanical cooling stages begin. Each unit’s cycling is slightly different, and is based on
the number of compressors and unloaders. The operational
loading sequence of compressors is as follows:
During the start-up of the lead compressor for each circuit, the low-pressure switch will be bypassed for 120 seconds to prevent nuisance trips of the low-pressure switch.
After start-up, a low-pressure trip will be ignored for 30 seconds by the processor.
SIZE 034,038 AND 048-088 UNITS — These units have 2
compressors and 2 unloaders on compressor 1. See Fig. 42
and 43 for compressor and condenser-fan motor locations.
The operating sequence is as follows:
Stage 1 Relays K1, K2, and K3 are energized. Compressor
no. 1 starts with both unloaders energized. Compressor no. 1 runs at 1⁄3 capacity. The crankcase
heater for this compressor has been deenergized,
and the first stage of condenser fans have been energized. Outdoor (condenser) fan motor no. 1
(OFM1) has started on all units.
Stage 2 Relays K1 and K3 are energized. Compressor
no. 1 is running with unloader 1 (U1) energized.
The compressor is now operating at 2⁄3 capacity.
Stage 3 Relay K1 is energized. Compressor no. 1 is fully
loaded.
Stage 4 Relays K1, K2, K3, and K5 are energized. Compressor no. 1 is running at 1⁄3 capacity, and compressor no. 2 is running at full capacity. The crankcase
heater for compressor no. 2 has been deenergized.
Stage 5 Relays K1, K3, and K5 are energized. Compressor
no. 1 is running at 2⁄3 capacity, and compressor
no. 2 is running at full capacity.
Stage 6 Relays K1 and K5 are energized. Both compressors are running fully loaded.
Size 034 and 038 units have 2 condenser fans, one of which
is controlled by the microprocessor. The OFM1 is energized
with compressor no. 1. The OFM2 is controlled by the processor and is cycled based on input from circuit thermistor
T3 or T4.
Size 048 units have one fan that can be controlled by the
processor. The other 2 are controlled by the compressors.
The OFM1 is energized by compressor no. 1, and OFM3 is
energized by compressor no. 2. The OFM2 is cycled by the
processor based on input from either circuit (thermistors T3
and T4).
On size 054,064 units, the first 2 condenser fans energize
with the compressors; compressor no. 1 controls OFM1, and
compressor no. 2 controls OFM2. The OFM3 and OFM4 are
staged by the microprocessor based on the condensing temperature input from thermistor T3 or T4.
On size 074-078 units, the first 3 condenser fans energize
with the compressors; compressor no. 1 controls OFM1, and
compressor no. 2 controls OFM2 and OFM3. The OFM4
and OFM5 are staged by the microprocessor based on condensing temperature input from either circuit’s T3 or T4
thermistor.
On Size 088 units, the first 4 condenser fans energize with
the compressors; compressor no. 1 controls OFM1 and OFM3,
and compressor no. 2 controls OFM2 and OFM4. The OFM5
and OFM6 are staged by the microprocessor based on
condensing temperature input from either circuit’s T3 or T4
thermistor.

Operating Sequence — The sequence presented below assumes that the unit is equipped with heat for morning
warm-up and an economizer. If these items are not enabled
with the appropriate DIP switches, the processor bypasses
these subroutines. This sequence is also based on an EPROM
(erasable, programmable, read-only memory) processor chip
with the identification ‘HT204485-1-XX,’ where ‘XX’ is replaced by a 2-digit number representing the current software
version. See Fig. 1 for EPROM chip location.
When power is applied to the occupied mode relay (OMR)
through the closure of either a field-installed timeclock or a
field-installed switch in the occupied space, the unit will begin its initialization mode.
A 20 will appear in the display screen, and the initialization period will last approximately 2 minutes. During this
time, the economizer dampers open and close to determine
the resistance range for full economizer operation of the economizer position potentiometer (P2). The processor loads the
necessary constants for unit operation, and also checks the
thermistors and other potentiometers for their values and validity. After the initialization period, the screen goes blank
until the display button is pressed.
Use caution during this time (after initialization when
the screen is blank), because the unit supply and return
fans could start at any time. Personal injury could result
from contact with rotating fans.
Once the initialization period is complete, the supply fan
begins operation. While the fan is operating, the economizer
dampers are closed and return air from the building is being
circulated. After 2 minutes, the processor checks the resistance value of thermistor T2. If T2 temperature sensed is
5° F or more below the set point of the morning warm-up
potentiometer (P6), the unit will begin the morning
warm-up routine, and a 26 will be displayed.
Unit heat will be energized through the heat interlock relay (HIR), and all of the occupied space air terminals open.
The unit will continue heating the space until the return-air
temperature is within 2° F of set point. The unit will then
shut off the heat and continue to circulate air. The unit will
cycle in and out of the heating mode until the return-air temperature reaches the morning warm-up set point (P6). Once
morning warm-up has been terminated, the unit cannot return to morning warm-up until the unit is powered down and
restarted. This action signals a return to the Occupied mode.
NOTE: Occupied heat is NOT AVAILABLE on these units.
Once out of the morning warm-up routine, the unit will
begin its cooling routine based on the supply-air set point
(P1). At step zero, the unit has no mechanical cooling on,
and the economizer may or may not be operational. The economizer will move to the minimum position determined by potentiometer P5 if no cooling load is detected. Once a cooling
load is detected by thermistor T1 sensing a temperature higher
than the cooling demand set point (P1), the economizer will
begin modulating to meet the load if the outdoor enthalpy is
good. The processor will attempt to maintain a supplyair temperature of P1 ± 2° F by modulating the economizer
dampers.
No mechanical cooling will take place until the economizer dampers are fully open (if the outdoor-air enthalpy
permits). If the economizer is unable to meet the cooling
demand, then mechanical cooling is used in conjunction with
the economizer. If the economizer is unable to meet the load
due to unacceptable outdoor-air enthalpy, the dampers will
return to the minimum position as determined by P5.
35

Stage 4

Relays K1 and K5 are energized. Both compressors no. 1 and no. 2 are running fully loaded.
Stage 5 Relays K1, K3, K5, and K5 are energized. Compressor no. 1 runs at 2⁄3 capacity and compressors
no. 2 and no. 4 are running at full capacity. The
crankcase heater on compressor no. 4 is deenergized. Fans OFM1, OFM2, OFM3, and OFM4 are
operating.
Stage 6 Relays K1, K5, and K6 are energized. Compressors no. 1, no. 2, and no. 4 are running fully loaded.
Stage 7 Relays K1, K2, K3, K5, and K6 are energized.
Compressor no. 1 runs at 2⁄3 capacity and compressors no. 2, no. 3, and no. 4 are running at full
capacity. Fans OFM1, OFM2, OFM3, and OFM4
are operating. Crankcase heater for compressor
no. 3 is deenergized.
Stage 8 Relays K1, K2, K5, and K6 are energized. Compressors no. 1, no. 2, no. 3, and no. 4 are running
fully loaded.
On Size 104 units, the first 4 condenser fans energize with
the compressors; circuit no. 1 compressors control OFM1
and OFM3, and circuit no. 2 compressors control OFM2 and
OFM4. The OFM5 and OFM6 are staged by the microprocessor based on condensing temperature input from
either circuit’s T3 or T4 thermistor.

SIZE 044 UNITS — These units have 2 compressors and 1
unloader on compressor no. 1. See Fig. 42 for compressor
and condenser fan motor locations. The unit operating sequence is as follows:
Stage 1 Relays K1 and K3 are energized. Compressor
no. 1 starts with the unloader energized. Compressor no. 1 is running at 1⁄2 capacity. The crankcase heater on compressor no. 1 has been deenergized, and the first stage condenser fan has been
energized. Outdoor (condenser) fan motor no. 1
(OFM1) has started.
Stage 2 Relay K1 is energized. Compressor no. 1 is fully
loaded.
Stage 3 Relays K1, K3, and K5 are energized. Compressor no. 1 is running at 1⁄2 capacity, and compressor no. 2 is running at full capacity. The crankcase
heater for compressor no. 2 is deenergized. The
second stage condenser fan has been energized.
Both OFM1 and OFM3 are operating.
Stage 4 Relays K1 and K5 are energized. Both compressors are running fully loaded.
Size 044 units have one fan that can be controlled by the
processor. The other 2 are controlled by the compressors.
The OFM1 is energized by compressor no. 1, and OFM3 is
energized by compressor no. 2. The OFM2 is cycled by the
processor based on input from either circuit (thermistors T3
and T4).
SIZE 104 UNITS — These units have 4 compressors and
1 unloader on compressor no. 1. See Fig. 43 for compressor
and condenser fan motor locations. The unit operating sequence is as follows:
Stage 1 Relays K1 and K3 are energized. Compressor
no. 1 starts with unloader energized. Compressor
no. 1 runs at 2⁄3 capacity. The crankcase heater for
this compressor has been deenergized, and first stage
of condenser fans has been energized. Outdoor (condenser) fan motor no. 1 (OFM1) and oudoor fan
motor no. 3 (OFM3) have started.
Stage 2 Relay K1 is energized. Compressor no. 1 is fully
loaded.
Stage 3 Relays K1, K3, and K5 are energized. Compressor no. 1 runs at 2⁄3 capacity and compressor
no. 2 is running at full capacity. The crankcase
heater for compressor no. 2 is deenergized. The
first stae of condenser fans on circuit 2 has been
energized. Fans OFM1, OFM2, OFM3, and OFM4
are operating.

034 AND 038 UNITS

Head Pressure Control — All units have as standard
a basic head pressure control function which allows the units
to operate in cooling down to 45 F. If cooling is required at
outdoor ambient temperatures lower than 45 F, refer to accessory head pressure control literature for details.
Head pressure control is handled by the processor. The
processor attempts to maintain the head pressure by cycling
the condenser-fan motors. No condenser fans will be running without a call for mechanical cooling. Thermistors T3
and T4 provide the condensing temperature information to
the processor. These VAV rooftop units have dual refrigeration circuits, and the higher circuit temperature will govern
unit operation. If the condensing temperature is above
133 F (236 psig), a condenser fan stage will be added. If the
condensing temperature is 78 F (142 psig) or less, the number of condenser fans operating will be decreased. After each
fan stage, the processor will wait one minute for the head
pressures to stabilize before changing again, unless thermistor T3 or T4 senses a temperature greater than 125 F
(278 psig), in which case all condenser fans are started.
During start-up, if the outdoor ambient is above 70 F (as
sensed by thermistor T3 or T4), the first-stage, processorcontrolled fans are turned on to prevent excessive discharge
pressures.

044 AND 048 UNITS

LEGEND
OFM — Outdoor (Condenser) Fan Motor

Fig. 42 — Component Arrangement, 034-048 Units
36

054, 064 UNITS

054-088 UNITS

074, 078 UNITS

088, 104 UNITS

104 UNITS

Fig. 43 — Component Arrangement, 054-104 Units

Supply Fan Control with IGV — In most VAV units,
the supply fan static pressure is controlled by inlet guide vanes.
The inlet guide vanes operate independently from the microprocessor. The supply static pressure is controlled by a differential pressure switch. If the unit is equipped with a return fan, building pressure is controlled by another differential
pressure switch.
For example, assume that set point on supply fan differential switch is 1.9 in. wg. If pressure in supply duct goes
above 1.9 in. wg, switch will make to the normally open
contact and energize inlet guide vane motor to drive inlet
guide vanes to a more closed position, thus reducing airflow
and lowereing duct pressure. Once set point pressure is reached,
switch will open and deenergize inlet guide vane motor. If
pressure in supply duct is below 1.9 in. wg, the switch will
make to the normally closed contact and energize inlet guide
vane motor to drive inlet guide vane to a more open position; increasing airflow and raising duct pressure. Once again,
once desired pressure has been reached, switch will open and
deenergize inlet guide vane motor. How far above or below
the set point setting the switch goes before energizing depends on setting of null span (null span is pressure change
that can be made without contacts opening or closing). If
null span is at maximum position, pressure will vary from
0.17 in. wg to 0.31 in. wg depending on set point (if set point
is at minimum setting, null span will be 0.17 in. wg, while
if it is at maximum position, the null span will be
0.31 in. wg) before switch acts. If null span is adjusted to a
minimum setting, duct pressure will vary from 0.06 in. wg
to 0.11 in. wg (again depending on switch set point) before
switch acts. Setting null span to minimum position will result in a smaller pressure fluctuation than if it is set at maximum position.

Modulating Power Exhaust (Option or Accessory except FY,JY units) — The power exhaust assembly consists of two parallel and independent belt-drive
forward curve fans. The fans, motors, and drives are located
over the return air opening of the unit, in a plenum beneath
the outside air intake plenum. The fans discharge air horizontally out the back of the unit through individual barometric backdraft dampers with hoods. (See Fig. 44 and 45.)
Operation is interlocked with economizer operation. Sheet
metal installation is shown in Fig. 46 and 47.
Fan no. 1 is equipped with a variable position discharge
damper located in the outlet of the fan housing. This damper
is controlled by an actuator (PEDM), based on signals from
the building pressure differential pressure switch (DPS). Available range on the DPS is −0.50 to +0.50 in. wg, adjustable.
Building pressure is sensed by a pick-up (field-supplied and
-installed) located in the occupied space.
Operation of the modulating power exhaust is a combination modulating/staged control, with fan no. 1 providing
modulating control from 0 to 100%, and fan no. 2 being staged
On/Off according to damper position on fan no. 1.
As the economizer actuator opens past 17% open, auxiliary switch DMS1 closes, energizing fan contactor PEC1.
Fan motor no. 1 starts and runs.
Capacity of fan no. 1 is controlled by the position of the
outlet damper. As building pressure increases above set point,
the DPS will close its contact and drive the power exhaust
damper motor (PEDM) open until set point is achieved. DPS
then opens its control contacts and PEDM maintains current
position.
When space demand moves PEDM to 90% of full-open
position, auxiliary switch PEDMS closes, energizing fan contactor PEC2. Fan motor no. 2 starts and runs. Increased exhaust airflow will lower space pressure, causing DPS to drive
PEDM back towards its closed position, until the set point
is achieved.
If space pressure decreases until PEDM position is reduced to 10% of open position, PEDMS will open, deenergizing fan contactor PEC2 and shutting off fan no. 2.

Supply Fan Control with VFD — When equipped
with the VFD option, the supply fan static pressure is controlled by modulating the fan wheel speed. The VFD operates independently from the microprocessor. A duct pressure
transducer monitors duct static pressure. The transducer output (4 to 20 mA) is directed into the VFD. The VFD adjusts
supply fan motor speed (which changes wheel speed) as measured duct pressure varies from set point as established at
the VFD. The VFD will modulate fan speed until the duct
pressure set point is achieved.
NOTE: The VFD will always provide the proper phase sequence to the supply fan motor. This motor will operate in
proper rotation regardless of the phase sequence to the unit.
If, upon start-up, the outdoor fans operate backwards but the
indoor fan operates in the correct direction, reverse any two
leads to the main terminal block. All fans will then operate
in the correct direction.

Unit Staging — Compressor loading and unloading sequences are shown in Table 19.

Fig. 44 — Modulating Power Exhaust Component Locations; Sizes 034-048

40
Fig. 45 — Modulating Power Exhaust Component Locations; Sizes 054-104

Fig. 46 — Modulating Power Exhaust Return End Sheet Metal Skin Detail; Sizes 034-048

Fig. 47 — Modulating Power Exhaust Return End Sheet Metal Skin Detail; Sizes 054-104
41

Table 19 — Compressor Loading and Unloading Sequences
COOLING
STAGE
0
1
2
3
4
5
6

OFF
ON
ON
ON
ON
ON
ON

COOLING
STAGE
0
1
2
3
4
5
6

Comp 1
OFF
ON
ON
ON
ON
ON
ON

COOLING
STAGE
0
1
2
3
4

COOLING
STAGE
0
1
2
3
4
5
6

Comp 1

Lead Circuit
Unloader
U1
OFF
ON
ON
OFF
ON
ON
OFF

SIZE 034 UNITS
Lag Circuit
Unloader
Comp 2
U2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
ON

Lead Circuit
Unloader
U1
OFF
ON
ON
OFF
ON
ON
OFF

SIZE 038 UNITS
Lag Circuit
Unloader
Comp 2
U2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
ON

SIZE 044 UNITS
Lag Circuit

Lead Circuit
Unloader
Comp 1
U1
OFF
OFF
ON
ON
ON
OFF
ON
ON
ON
OFF

Comp 1
OFF
ON
ON
ON
ON
ON
ON

Lead Circuit
Unloader
U1
OFF
ON
ON
OFF
ON
ON
OFF

Percent
Capacity

0
2
4
6
8
10
12

0
17
33
50
67
83
100

Active
Cylinders

Percent
Capacity

0
2
4
6
6
8
10

0
14
28
42
72
86
100

Comp 2

Active
Cylinders

Percent
Capacity

OFF
OFF
OFF
ON
ON

0
2
4
6
8

0
25
50
75
100

SIZE 048 UNITS
Lag Circuit
Unloader
Comp 2
U2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
ON

Active
Cylinders

Percent
Capacity

0
2
4
6
6
8
10

0
19
38
58
62
81
100

Table 19 — Compressor Loading and Unloading Sequences (cont)
COOLING
STAGE
0
1
2
3
4
5

COOLING
STAGE
0
1
2
3
4
5
6

COOLING
STAGE
0
1
2
3
4
5
6
7
8

Comp 1
OFF
ON
ON
ON
ON
ON

Lead Circuit
Unloader U1
OFF
ON
ON
OFF
ON
OFF

SIZE 054 UNITS
Lag Circuit
Unloader U2
Comp 2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
OFF
ON
OFF
ON

Comp 1
OFF
ON
ON
ON
ON
ON
ON

Lead Circuit
Unloader U1
OFF
ON
ON
OFF
ON
ON
OFF

SIZE 064 UNITS
Lag Circuit
Unloader U2
Comp 2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
ON

Comp 1
OFF
ON
ON
ON
ON
ON
ON

Lead Circuit
Unloader U1
OFF
ON
ON
OFF
ON
ON
OFF

SIZE 074, 078 UNITS
Lag Circuit
Unloader U2
Comp 2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
ON

Comp 1
OFF
ON
ON
ON
ON
ON
ON

Lead Circuit
Unloader U1
OFF
ON
ON
OFF
ON
ON
OFF

SIZE 088 UNITS
Lag Circuit
Unloader U2
Comp 2
OFF
OFF
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
ON

Comp 1
OFF
ON
ON
ON
ON
ON
ON
ON
ON

Lead Circuit
Unloader U1
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF

Comp 3
OFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON

SIZE 104 UNITS
Lag Circuit
Comp 2
Comp 4
OFF
OFF
OFF
OFF
OFF
OFF
ON
OFF
ON
OFF
ON
ON
ON
ON
ON
ON
ON
ON

Active
Cylinders

Percent
Capacity

0
2
4
6
10
12

0
20
40
60
80
100

Active
Cylinders

Percent
Capacity

0
2
4
6
8
10
12

0
17
33
50
67
83
100

Active
Cylinders

Percent
Capacity

0
2
4
6
8
10
12

0
14
29
43
71
86
100

Active
Cylinders

Percent
Capacity

0
2
4
6
8
10
12

0
16
33
50
66
83
100

Active
Cylinders

Percent
Capacity

0
4
6
10
12
14
16
18
20

0
20
30
50
60
70
80
90
100

Table 21 — Operation Status Codes

TROUBLESHOOTING
By using the display module, actual operating conditions
of the unit are displayed while it is running. The Quick Test
function allows proper operation of compressors, compressor unloaders, fans, and other components to be checked while
unit is stopped. If an operating fault is detected, an alarm is
generated and an alarm code(s) is displayed. For checking
specific items, see Table 20.

CODE

Checking Display Codes — To view the digital display codes, press the button located to the right of the LED
display/set point board in the control box. See Table 21 for
Operational Status Codes. See Table 22 for Diagnostic Codes.

MEANING

0
□

0 cooling stages active

1
□

1 cooling stage active

2
□

2 cooling stages active

3
□

3 cooling stages active

4
□

4 cooling stages active

5
□

5 cooling stages active

are several conditions that can cause this situation to occur:
• Remote ON/OFF circuit in Unoccupied mode.
• Unit ON/OFF switch moved to OFF position.
• Programmed schedule at the timeclock.
• General power failure.
• Blown fuse in the control power feed.
• Open control circuit fuse.
• Operation of the unit blocked by the demand limit
function.
• Unit supply-air temperature (T1) thermistor failure.
• Supply-air fan is not operating.
• High duct static pressure.

6
□

6 cooling stages active

7
□

7 cooling stages active

8
□

8 cooling stages active

20
□

Initialization mode (Allow 2 minutes
for initialization. To initiate Quick Test,
press the Display button while 20 is displayed.)

21
□

Temperature Reset in effect

22
□

Demand Limit in effect

Single Circuit Stoppage — If a single circuit stops,

26
□

Morning Warm-Up in effect

30
□

Internal failure detected

88
□

Self-diagnostic mode in effect

Complete Unit Stoppage — If the unit is off, there

there are several potential causes:
• Open contacts in the compressor high-pressure switch.
• Low refrigerant pressure.
• Thermistor failure.
• Unit supply-air temperature thermistor (T1) failure.
• Compressor circuit breaker trip.
• Operation of the circuit blocked by the demand limit
function.

Restart Procedure — Before attempting to restart the
machine, check the display for alarm codes to determine the
cause of the shutdown. If the unit, circuit, or compressor stops
more than once as a result of a safety device, determine and
correct the cause before attempting to start the unit again.
After the cause of the shutdown has been corrected, unit
restart may be automatic or manual depending upon the fault.

Table 20 — Controls Troubleshooting
SYMPTOM(S)
Controls do not seem
to be operating.
Evaporator fan does not run.
Compressor does not run.

Condenser fans do not
turn on.
Cooling demand exists and
economizer modulates, but
compression is not operating.

PROBABLE CAUSE(S)
Remote on-off function may be
keeping controls off.
1. Circuit breaker open.
2. Inverter overload (if equipped).
1. Circuit breaker is open.
2. There is no demand for cooling.
3. The control is locking out cooling operation.
4. Demand Limit in effect.
Circuit breaker is open.
Compression cannot be initiated
until economizer damper is 90% open.

SOLUTION(S)
Check status.
1.
2.
1.
2.
3.

Find cause and reset circuit breaker.
Find cause and reset.
Find cause and reset circuit breaker.
Correct operation.
Check rotating display for alarm codes. Resolve
alarm cause and reset control by changing to
standby and back to run mode.
4. Check Demand Limit Settings.
Find cause and reset circuit breaker
Correct operation.

Code 51 is for compressor 1, and Code 55 is for compressor 2. Codes 52 and 56 are used for compressors 3 and
4, respectively, on size 104 units.
The microprocessor has also been programmed to indicate a compressor failure if CR switch is closed when compressor is not supposed to be on.
If a failure occurs, the following are possible causes:
High-Pressure Switch Open — The high-pressure switch for
each compressor is wired in series with 24-v power that energizes CR. If high-pressure switch opens during operation,
CR will stop compressor and this will be detected by microprocessor through the feedback contacts.
Internal Thermostat — The internal thermostat in each 06D
compressor is also wired in series with 24-v power that energizes CR. If thermostat fails or switch opens during operation of compressor, compressor will shut down and failure is detected through feedback contacts (size 034 and 038
only).
CR Failure — If CR fails with large relay either open or closed,
microprocessor will detect this, lock compressor off, and indicate an error.
Relay Board Failure — If small 24-v relay on the relay board
fails, microprocessor will detect this through feedback contacts and indicate an error.
Processor Board Failure — If hardware that monitors feedback switch fails and processor board fails to energize the
relay board relay to ON position, an error may be indicated.
The control does not detect compressor circuit breaker
failures.
Wiring Problem — A wiring error or a loose wire may cause
the feedback circuit to be broken.

Diagnostic Codes — Diagnostic codes are warnings
of abnormal or fault conditions, and may cause either one
circuit or the whole unit to shut down. They are assigned
code numbers as described below.
Table 22 contains a description of each diagnostic code
error and possible cause. Manual reset is accomplished by
moving the ON/OFF Switch to the OFF position, then back
to ON.
The 2-digit LED display is used to display the diagnostic
codes and the alarm light (located next to display) is energized whenever a diagnostic code is tripped. When a problem is suspected, always check the display first for diagnostic information.
NOTE: Codes 53, 54, 57, 58, 61, 62, 65-69, 73, 74, and 77-80
are not used on these units.
IMPORTANT: The microprocessor memory and the
display will be cleared if the power to the microprocessor is shut off. DO NOT attempt to bypass, short, or
modify the control circuit or electronic boards in any
way to correct a problem. This could result in a hazardous operating condition.
CODES 51, 52, 55, 56: COMPRESSOR FAILURE — If control relay (CR) opens while compressor should be operating,
compressor will stop and microprocessor will energize alarm
light and display a code of 51 , 52 , 55 or 56 (depending on compressor) when display button is pushed. The
compressor will be locked off; to reset, the ON-OFF switch
must be turned to OFF and then to ON position.
If lead compressor in a refrigerant circuit is shut down,
the other compressor in that circuit will also be shut down
and locked off. Only the error code for the lead compressor
will be displayed.

Table 22 — Diagnostic Codes
DISPLAY

DESCRIPTION OF FAILURE
1
2
3
4

failure
failure
failure
failure

ACTION TAKEN
BY CONTROL
Circuit 1 shut off
Circuit 2 shut off
Compressor 3 shut off
Compressor 4 shut off

RESET
METHOD
Manual
Manual
Manual
Manual

51
55
52
56

Compressor
Compressor
Compressor
Compressor

59
60

Loss-of-charge circuit 1
Loss-of-charge circuit 2

Circuit 1 shut off
Circuit 2 shut off

Manual
Manual

63
64
70
71
72
75

Low oil pressure circuit 1
Low oil pressure circuit 2
Illegal unit configuration
Supply-air thermistor failure
Return-air thermistor failure
Circuit 1 saturated condensing thermistor

Circuit 1 shut off
Circuit 2 shut off
Unit will not start
Unit shut off
Use default value
Unit shut off

Manual
Manual
Manual
Auto.
Auto.
Auto.

Circuit 2 saturated condensing thermistor

Unit shut off

Auto.

81
82
83
84
85
86
87

Reset temperature thermistor failure
Leaving-air set point potentiometer failure
Economizer potentiometer failure
Reset limit set point potentiometer failure
Demand limit potentiometer failure
Minimum economizer potentiometer failure
Warm-up set point potentiometer failure

Stop reset
Use default value
Close economizer
Stop reset
Stop demand limit
Close economizer
Use default value

Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.

NOTES:
1. Illegal unit configuration caused by missing programmable header or both unloader DIP switches on.
2. All auto. reset failures that cause the unit to stop will restart when the error has been corrected.
3. All manual reset errors must be reset by turning the control switch off and then back on.
4. Valid resistance range for the thermistors is 363,000 to 585 ohms.
5. Codes 53, 54, 57, 58, 61, 62, 65-69, 73, 74, and 77-80 are not used on these units.

PROBABLE CAUSE
High-pressure switch or high discharge gas thermostat switch
trip, compressor ground current
. 2.5 amp or compressor board
relay on when it is not supposed
to be on. Wiring error between
electronic control and compressor protection module.
This indicates either a low refrigerant charge, or a loss-of-charge
switch failure.
Not used; Check jumper on processor board.
Configuration error (see Note 1).
Thermistor or resistor failure, wiring error, or thermistor or resistor
not connected to the processor
board.

Potentiometer improperly connected, potentiometer setting out
of range, potentiometer failure or
wiring error.

CODE 82: LEAVING-AIR TEMPERATURE SET POINT
POTENTIOMETER FAILURE — If leaving-air set point potentiometer (P1 — located on display board) fails, control
will use a default value. A failure will cause an error code of
82 to be displayed on display board when display button is
pushed; alarm light will also be energized. A failure is determined by establishing a range of −22 F to 70 F as a valid
range. Anything outside this range will be treated as a failure. If setting is outside the −22 F to 70 F range, alarm light
will be energized and an error code of 82 will be displayed
when display button is pushed; the control will use a set point
of 70 F. If set point is between −22 F and 45 F, control will
use a set point of 45 F and no error code will be indicated.
If potentiometer returns to normal, control will automatically reset.
NOTE: The full range of the potentiometer is not used for
the cooling set point range of 45 F to 70 F. The full scale
resistance of the potentiometer is 10 Kohms.
If a failure occurs, one of the following is a probable cause:
Incorrect Potentiometer Setting — A potentiometer turned fully
clockwise or counterclockwise is outside the valid range and
will cause a failure.
Faulty Wiring — If wiring is incorrect between potentiometer and processor board or display board, a failure will
result.
Potentiometer Failure — If potentiometer is shorted or open,
a failure will result.
CODE 83: ECONOMIZER FEEDBACK POTENTIOMETER FAILURE — If potentiometer on economizer motor
(P2) fails, control will use a default value of 0% and economizer outdoor-air dampers will close. The failure will energize alarm light and cause an error code of 83 to be displayed when display button is pushed. This potentiometer is
a 5 to 15 Kohm potentiometer. If potentiometer returns to
normal, control will automatically reset. If a failure occurs,
one of the following is the probable cause.
Faulty Wiring — If the wiring between processor board and
potentiometer is wrong, this will cause a failure.
Potentiometer Failure — If potentiometer is shorted or open,
this will cause a failure.
Economizer Damper Stuck — The control has been programmed to indicate an error if potentiometer travel is less
than 10% of the full range. This would happen if dampers or
damper linkage were hung up and could not move
properly.
CODE 84: RESET LIMIT POTENTIOMETER FAILURE
— This code is applicable only if reset is being used. If reset
is being used, DIP switch 2 must be in the ON position. This
potentiometer (P3) is located on the accessory board. If potentiometer setting is less than 0° F or greater than 80 F,
alarm light will be energized, a diagnostic code of 84 will
be displayed if display button is pushed, and reset will be
terminated. The full-scale resistance of potentiometer is
10 Kohms, but when installed on the accessory board in parallel with the other 2 potentiometers, measured resistance
will be 3.3 Kohms. This failure will automatically reset once
potentiometer returns to normal. If a failure occurs, one of
the following is the probable cause:
DIP Switch Problem — DIP switch 2 is in the ON position
and the accessory board is not installed (accessory board is
standard on these units so it should always be on the unit).

CODES 59 AND 60: LOW-PRESSURE SWITCH — These
codes are used to indicate a low-pressure switch failure.
The processor monitors the low-pressure switch. If the switch
opens, either by low refrigerant charge, circuit failure, or wiring error, the circuit is locked off. Code 59 indicates a failure
of the lead circuit, and as a result, that circuit will be shut
down. Code 60 indicates a failure of the lag circuit, and as
a result, that circuit will be shut down. These codes will only
be displayed when the display button is pressed. To reset the
circuit, the ON-OFF switch must be turned to OFF, then ON
position.
CODES 63 AND 64: OIL PRESSURE SWITCH — These
codes are used to indicate an oil pressure switch failure. Since
the units do not have oil pressure switches, these codes are
not used. The terminals on the processor board must be jumpered together or an error will occur. If these errors occur,
check jumper between J2-1 and J2-2 for a code 63, or between J2-3 and J2-4 for a code 64 to be sure jumper is properly connected. To reset the circuit, the ON-OFF switch must
be turned to OFF and then to ON position.
CODE 70: ILLEGAL UNIT CONFIGURATION — If the
unit configuration header is not installed and properly configured, and/or if DIP switches are not properly set, unit will
not start, and an error code of 70 will be indicated on display
board when display button is pushed. Check the header and
DIP switch settings.
CODES 71 TO 76: THERMISTOR/RESISTOR FAILURE
— If measured temperature of a thermistor is less than
−60 F (363,000 ohms) or greater than 180 F (585 ohms), the
appropriate sensor error code (Table 22) will be displayed
when the display button is pushed. The unit will be shut down.
Thermistor failures will automatically reset once the error
has been corrected. If a failure occurs, the following are possible causes:
Thermistor or Resistor Failure — A shorted or open thermistor or resistor will cause the failure.
Wiring Failure — If a wiring error exists that causes a shorted
or open circuit, this will cause a failure.
Processor Board Failure — If circuitry on processor board
fails, this could cause an error.
The codes are designated as follows:
Code 71 Supply-Air Thermistor Failure
Code 72 Return-Air Thermistor Failure
Code 73 Not used
Code 74 Not used
Code 75 Circuit 1 Saturated Condensing Thermistor
Code 76 Circuit 2 Saturated Condensing Thermistor
CODE 81: RESET THERMISTOR OR POTENTIOMETER FAILURE — This is a unique code since the reset
temperature potentiometer (P7) is in series with the space
temperature thermistor (T10). If either one of these components fail, reset will be terminated. This error will automatically reset once the situation is corrected. If an error is
detected, the most probable cause is one of the following:
• Thermistor Failure — A shorted or open thermistor will
cause the failure.
• Potentiometer Failure — If the potentiometer is outside of
the valid range (40 to 90 F), a failure will result.
• Wiring Problem — If the circuit is open, a failure will be
detected.
• Processor Board Failure — If the processor board fails (hardware), an alarm will be detected.

potentiometer (P6) is located on the accessory board. If potentiometer is set at less than 0° F or more than 95 F, alarm
light will be energized, a diagnostic code of 87 will appear on the display when display button is pushed, and control will use a default value of 40 F. If setting is between
0° F and 40 F, control will use a value of 40 F but no diagnostic code will be displayed; if setting is between 80 F
and 95 F, control will use a value of 80 F but no diagnostic
code will be displayed.
The potentiometer full-scale resistance is 10 Kohm, but
when wired in parallel with other potentiometers on the accessory board, measured resistance is 3.3 Kohm.
The failure will automatically reset once potentiometer returns to normal. If a failure occurs, one of the following is
the probable cause:
DIP Switch 4 — If this switch is in the ON position and the
accessory board is not installed (accessory board is standard
on these units, so it should always be on the unit).
Incorrect Potentiometer Setting — If potentiometer is turned
fully clockwise or counterclockwise, potentiometer will be
out of the allowable range, resulting in an error.
Faulty Wiring — If the wiring between the potentiometer and
the processor board is incorrect, an error will occur.
Potentiometer Failure — If potentiometer is shorted or open,
potentiometer will be out of range, resulting in an error.

Incorrect Potentiometer Setting — A potentiometer turned fully
clockwise or counterclockwise is outside the valid range and
will result in a failure.
Faulty Wiring — If the wiring between the potentiometer and
the processor board is incorrect, a failure will result.
Potentiometer Failure — If potentiometer is shorted or open,
a failure will occur.
CODE 85: DEMAND LIMIT POTENTIOMETER (P4) FAILURE — Used only if demand limit is being used. If demand
limit is used, DIP switch 5 must be in the ON position.
Two types of demand limit are available: a field-supplied
and installed single-step control consisting of a 10 Kohm,
3-wire linear potentiometer and an accessory 2-step control
are available from Carrier. The single-step control has a single
potentiometer while 2-step control has 2 potentiometers
(mounted on the demand limit board, see Fig. 26).
For both types of demand limit, the control uses only 80%
of the total potentiometer resistance. If resistance of potentiometer is less than 10% or greater than 90%, alarm light
will be energized, a diagnostic code of 85 will be displayed
when the display button is pushed, and demand limit will be
terminated. If a failure occurs, it is probably due to one of
the following:
Potentiometer Failure — If a potentiometer is shorted or open,
a failure will occur.
Incorrect Potentiometer Setting — A potentiometer turned fully
clockwise or counterclockwise will put potentiometer out of
range resulting in an error.
Faulty Wiring — If wiring between the potentiometer and
the processor board is incorrect, an error will occur.
DIP Switch 5 — If DIP switch 5 is in the ON position and
potentiometer is not installed, an error will occur.
CODE 86: MINIMUM POSITION ECONOMIZER POTENTIOMETER FAILURE — If potentiometer P5 (on accessory board) setting is less than 0% or greater than 100%,
alarm light will be energized, a code of 86 will be displayed when display button is pushed and economizer outdoor air dampers will move to the fully closed position.
The potentiometer full-scale resistance is 10 Kohm, but
when installed in parallel with the other 2 potentiometers on
the accessory board, measured resistance will be 3.3 Kohm.
This failure will automatically reset when potentiometer
returns to normal.
If a failure occurs, one of the following is the probable
cause:
DIP Switch 3 — If this switch is in the ON position and the
accessory board is not installed (accessory board is standard
on these units, so it should always be on the unit).
Incorrect Potentiometer Setting — If potentiometer is turned
fully clockwise or counterclockwise, potentiometer will be
out of the allowable range, and an error will result.
Faulty Wiring — If wiring between the potentiometer and
the processor board is incorrect, an error will occur.
Potentiometer Failure — If potentiometer is shorted or open,
potentiometer will be out of range and an error will result.
CODE 87: WARM-UP TEMPERATURE SET POINT FAILURE — Applicable only if morning warm-up is used. Whether
or not unit is equipped with electric resistance heaters, use
of the morning warm-up function is recommended if the unit
is shut down at night or over weekends. In this application,
cooling will remain off and the outdoor-air damper will stay
closed until heat load from the occupied space elevates returnair temperature to the warm-up set point. If warm-up function is used, DIP switch 4 must be in the ON position. The

Thermistor Troubleshooting — The VAV control system uses thermistors to measure temperatures of the entering and supply air, as well as the saturated condensing temperatures of the refrigerant circuits. The resistance versus
temperature and electrical characteristics for all thermistors
in the system are identical. To obtain an accurate reading, a
high-impedance meter (such as a digital meter) must be used.
Thermistors in the VAV control system have a 5 vdc signal applied across them any time the unit control circuit
is energized. The voltage drop across the thermistor is directly proportional to the temperature and resistance of the
thermistor.
To determine temperatures at the various thermistor locations, disconnect the thermistor from the processor board
and measure the resistance across the appropriate thermistor
using a high-quality digital ohmmeter. Use the resistance reading to determine the thermistor temperature.
The microprocessor has been programmed to check the
operation of the thermistors. If the measured temperature is
outside of the range of −24 to 225 F or 98,010 to 282 ohms,
then it will be treated as a sensor failure and a diagnostic
code will be displayed. See Table 17 for sensor temperatures
versus resistance drop. It is also possible to check the operation of the thermistors using the quick test routine.
If a thermistor has failed or the wire is damaged, replace
the complete assembly. Do not attempt to spice the wires or
repair the assembly.

Electronic Controls Checkout — The following will
help determine whether a processor board, a relay board, display set point board, accessory board, or 2-step demand limit
module is faulty.
Before checking out any board, do the following:
1. At initial start-up, enter the Quick Test mode. This test
will determine if all components are connected and operating properly.
2. If system has been operating and a malfunction occurs,
check display for diagnostic codes. Use diagnostic chart
located on inner panel of access door to control box section of unit; this chart will help determine probable cause
of failure.
47

Step 3 — Check Voltage Tolerance Circuitry
1. Turn power to OFF position.
2. Negative test probe on TP18 and system in Quick Test
mode.
3. Check voltage TP18 to TP9.
4. If voltage is greater than 11 vdc, recheck transformer
input voltage.
5. If transformer is okay, replace processor board.
6. Turn power to ON position.
Step 4 — Check Processor Reset Line
1. Turn power to OFF position.
2. Negative probe on TP18.
3. Check voltage TP18 to TP11.
4. If voltage is greater than 13 vdc, reset power and
recheck.
5. If voltage is still incorrect, replace processor board.
6. Turn power to ON position.

These 2 steps will help determine if a component other
than a board is at fault or if the problem is external to control
circuit.
A volt-ohmmeter will be needed to troubleshoot boards. A
digital meter is preferred but a Simpson 260 or equivalent
will work.

To prevent damage to solid-state electronic components
on boards, meter probes should only be placed on terminals and test points listed in following sections. Do
not short the electrical components, and use extreme care
while working on the processor board.
PROCESSOR BOARD CHECKOUT — Refer to Fig. 48
and 49 for location of terminal pins and test points.
Step 1 — Check Transformer Input to the Board — Connector
J4 is used to connect the control transformer to the processor
board.
1. Set the volt-ohmmeter to ac voltage with a range setting
of approximately 30 v.
2. Turn control switch to ON position.
3. Check voltage at following terminals on pin terminal connector J4:
VOLTAGE (AC)
15.3 to 20.9
16.2 to 22.0
8.1 to 11.0
8.1 to 11.0

4. If voltage is not within range, check primary side.
115-v transformer — 104 to 127 vac
230-v transformer — 207 to 254 vac
5. If primary voltage is not correct, check system fuse, transformer, ON-OFF switch, and wiring. If these are okay,
contact power company.
6. If primary voltage is correct, but secondary voltage
(24 v ± 10%) is incorrect, replace transformer.
7. Turn control switch to OFF position.
Step 2 — Check Processor Board Power Supply
1. Set meter to approximately 20 vdc.
2. Turn power to OFF position.
3. Connect negative lead to TP18.
4. Turn power switch to ON position and press display button to enter Quick Test mode.
5. Check voltage between TP18 and each of the following
test pins:

Fig. 48 — Processor Board Test Points
J6

R10

R11

R12

R13

C10

C11

C12

C13

CR9

CR1

CR2

CR3

6. If voltage is incorrect, replace processor board.
7. Turn power to ON position.

CR4

CR5

CR6

C19

C27
C15
C14

*If not using a digital meter, leads must be reversed.

C21

CR10

CR11

CR12

CR7

CR8

C26
C25
C24
C23
C22

VOLTAGE (DC)
110
112
15
15
112
112
−5*

C16

TEST PIN
TP3
TP4
TP6
TP10
TP14
TP15
TP7

LEGEND
J — Pin Terminal Strip
TP — Test Pin

C18

TERMINALS
1 to 2
4 to 6
5 to 6
5 to 4

LEGEND
CR — Control Relay
J
— Pin Terminal Strip
K — Relay

Fig. 49 — Relay Board Test Points
48

CR13

5. Place the other lead on terminals shown in table below,
and check voltage at pin terminals on pin terminal connector J10 (see Fig. 51 for pin terminal connector J10
details):

Step 5 — Check Relay Board Outputs from the Processor
Board — This step involves checking the output signals from
relays K1-K3 on the relay board.
1. Turn power to OFF position.
2. Connect negative test probe to TP19 (meter still set to
dc).
3. Turn switch to ON position and enter Quick Test mode.
4. Connect positive test probe to terminal 14 on pin terminal connector J9, and check voltage from TP19 to terminal 14 on pin terminal connector J9.
5. If not 112 ± 1 vdc, replace processor board.
6. Turn switch to OFF position.
7. Remove negative test probe from TP19. Connect positive
test probe to TP15.
8. Turn switch to ON position and go into Quick Test mode.
9. Place negative lead on terminals shown in Table 23, and
check voltage between TP15 and terminals shown in
Table 23 on pin terminal connector J9. See Fig. 50 for J9
details.

PIN TERMINAL
17
18
20*
22*
24

VOLTAGE (DC)
5
5
2.5
2.5
5

*Voltage reading is dependent on the meter’s impedance. Readings
may vary with different meters.

6. If voltage is not correct, replace processor board.
Step 7 — Potentiometer Connection Checkout.
1. Turn power to OFF position.
2. Remove plug connection from pin terminal strip J3.
3. Connect negative meter lead to terminal 2 of J3.
4. Turn switch to ON position and go into Quick Test mode.
5. Place the other lead on terminals shown in table below,
and check voltage at pin terminals on terminal connector
J3:
PIN TERMINAL
1*
3
6
8*
10*
12
13*
14*

VOLTAGE (DC)
2.5
5
5
2.5
2.5
5
2.5
2.5

*Voltage reading is dependent on the meter’s impedance. Readings
may vary with different meters.

6. If voltage is not correct, replace processor board.
Step 8 − Thermistor Input Connector Checkout
1. Turn power to OFF position.
2. Remove the thermistor connections from pin terminal connector J1, and mark them for later replacement.
3. Connect the negative test lead to test pin TP18.
4. Turn power to ON position, and enter the Quick Test
routine.
5. Place the other lead on terminals shown in Table 24, and
check the voltages.
6. If voltages are incorrect (per Table 24), replace processor
board.
7. Turn power to OFF position, and replace the thermistor
connections removed in Step 2.
8. Turn power to ON position.

Fig. 50 — Relay Board Pin Terminal Connector (J9)

Table 23 — Voltage Reading
J9 PIN NUMBERS
QUICK TEST
STEP NO.
1 2 3 4 5 6 7 8 9 10 11 12 13
1.-2.3.
0 0 0 0 0 0 0 0 0 0 0 0 12
2.4.
0 0 0 0 0 0 12 0 0 0 0 0 12
2.5.
0 0 0 0 0 0 0 12 0 0 0 0 12
2.6.
0 0 0 0 0 0 0 12 0 12 0 0 12
2.7.
0 0 0 0 0 0 0 12 0 0 12 0 12
2.8.
0 0 0 0 0 0 0 12 0 0 0 12 12
2.9.
12 0 0 0 0 0 0 12 0 0 0 0 12
3.0.
0 12 0 0 0 0 0 12 0 0 0 0 12
3.1.
0 0 12 0 0 0 0 12 0 0 0 0 12
3.2.
0 0 0 0 12 0 0 12 0 0 0 0 12
3.3.
0 0 0 0 0 12 0 12 0 0 0 0 12
NOTES:
1. Pins shown in boldface type will only be energized for 10 seconds. All other pins will be energized continuously while at the proper
quick test step. The control will only stay in the Quick Test routine
for 10 minutes unless the display button is pressed.
2. Acceptable range for the voltage reading:
0 v — 0 to 4 v
12 v — 11 to 13 v
3. If any of these voltages are not measured, replace the processor
board.

Step 6 — Display Board Connection Checkout
1. Turn power to OFF position.
2. Disconnect the ribbon cable.
3. Connect negative lead of meter to TP18.
4. Turn power to ON position and go into Quick Test mode.
Fig. 51 — Display Board Pin Terminal Connector (J10)
49

Table 24 — Pin Terminal Connector J1 Voltages
PIN
TERMINAL
1
2
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

The following procedure can be used to check out the operation of the relays. To do this, turn the control ON/OFF
switch to the OFF position, and remove the wiring connectors connected to pin terminal connectors J5 and J6. Set the
meter for resistance. If the contacts do not close at the required quick test step, check the relay outputs from the processor board.
Relay Board Checkout (Fig. 5)
Step 1 — Low-voltage relay resistance check.
1. Turn switch to OFF position.
2. Remove plug connection from terminal strip J6.
3. Set meter to measure resistance. Connect negative test
lead to both terminals 11 and 12 of J6.
4. Turn switch to ON position and go into quick test mode.
5. Place other meter lead on terminals shown in Table 26
and check resistances at each quick test step.
6. If these resistances are not correct and relay board outputs from processor board have been checked out, replace relay board.
Step 2 — High-voltage relay resistance check.
1. Turn switch to OFF position.
2. Remove plug connection from terminal connector J5.
3. Connect negative test lead to terminal 8.
4. Check the resistance between terminals 8 and 5 before
entering Quick Test mode. The resistance should be
infinity.
5. Turn switch to ON position and go into Quick Test mode.
6. Place other meter lead on terminals shown in Table 27
and check resistance at each quick test step.
7. If these resistances are not correct and relay board outputs from processor board have been checked per Processor Board Checkout section on page 48, replace relay
board.
DISPLAY BOARD CHECKOUT
Step 1 — Check the Output Voltage from Processor Board
to the Relay Board — Refer to Step 6 — Display Board Connection Checkout section on page 49.

VOLTAGE
(vdc ± 0.25 v)
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
5

Step 9 − Thermistor Input Connector Checkout
1. Turn power to OFF position.
2. Disconnect all plugs for pin terminal connector J2 and
mark them for later replacement.
3. Connect a negative test lead to test pin TP18.
4. Turn power to ON position, and enter the Quick Test
routine.
5. Place the other lead on terminals shown in Table 25, and
check the voltages.
6. If voltages are incorrect (per Table 25), replace processor
board.
7. Turn power to OFF position, and replace the plugs removed in Step 2.
8. Turn power to ON position.
Table 25 — Pin Terminal Connector J2 Voltages
PIN
TERMINAL
1
2
3
4
7
8
9
10
13
14
15
17
18
19
20
21
22
23
24

VOLTAGE
(vdc ± 0.25 v)
0
5
0
5
0
5
0
5
0
5
5
5
5
5
5
5
5
5
5

Table 26 — Terminal Strip J6 Connection
Resistance Reading
QUICK TEST
STEP NO.
1. to 2.3.
2.4.
2.5.
2.6.
2.7.
2.8.
2.9.
3.0.
3.1.
3.2.
3.3.

If Steps 1 through 9 have been competed and the unit still
will not function properly, replace the processor board.

1
`
`
`
`
`
`
0
`
`
`
`

2
`
`
`
`
`
`
`
0
`
`
`

J6 PIN NUMBERS
3
4
5
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
0
`
`
`
`
0
`
`
`

6
`
`
`
`
`
`
`
`
`
`
0

7
`
0
`
`
`
`
`
`
`
`
`

8
`
`
0
`
`
`
`
`
`
`
`

LEGEND
` — Infinity

RELAY BOARD TROUBLESHOOTING — The relay board
contains 13 electromechanical relays. The small relays are
24 vac, and the large relays are 115 vac. These relays are
controlled by the processor through the ribbon cable attached to the relay board.

NOTE: Pins shown in boldface type will be energized for only
10 seconds. All other pins will be energized continuously while at the
proper quick test step. The control will remain in the Quick Test mode
for only 10 minutes unless the display button is pressed.

Table 27 — Terminal Strip J5 Connector
Resistance Reading
QUICK TEST
STEP NO.
1. to 2.5.
2.6
2.7.
2.8.
2.9. to 3.3.

1
`
0
0
0
0

J5 PIN NUMBERS
2
3
4
`
`
`
0
`
`
`
0
`
`
`
0
`
`
`

IMPORTANT: Be careful to avoid damaging the connector or the processor board when taking the voltage
readings.
5
0
0
0
0
0

Test under the following conditions:
• No power to IN1 or IN2
Terminal 1 to 2 should read 4.5 vdc ±0.1 v
Terminal 2 to 3 should read 5.0 vdc ±0.1 v
• Power to IN2 or to both IN1 and IN2, and P2 set at 24%
Terminal 1 to 2 should read 1.5 vdc ± 0.1 v
NOTE: Voltage should vary between 0.5 vdc and 2.5 vdc
as the setting of P2 is varied between 0% and 49%.
Terminal 2 to 3 should read 5.0 vdc ± 0.1 v
• Power to IN1 only and P1 set at 50%
Terminal 1 to 2 should read 2.5 vdc ± 0.1 v
Terminal 2 to 3 should read 5.0 vdc ± 0.1 v
NOTE: Voltage should vary between 0.5 vdc and 2.5 vdc
as the setting of P2 is varied between 50% and 100%.
NOTE: If the voltages listed in these 3 tests are not obtained
during testing, the DLCM board must be replaced.

LEGEND
` — Infinity

Step 2 — Check the Display LEDs
1. Enter Quick Test mode.
2. If 88 is not displayed, replace display board.
Step 3 — Check Set Point Potentiometer — Advance the display to quick test step 1.9. to determine if this potentiometer
is set and connected properly.
Step 4 — Check Display Switch — Press switch. If switch
does not click, it is faulty and the display will be energized
continuously. The switch is an integral part of display board
and cannot be replaced separately.

Enthalpy Sensor Checkout — To test operation of
enthalpy sensor, see Table 28.
Table 28 — Enthalpy Sensor Checkout

ACCESSORY BOARD CHECKOUT — The accessory board
can be completely checked using quick test steps 2.0., 2.2.,
and 2.3. It can also be checked out as follows:
1. Remove the accessory board connector from the processor board and connect an ohmmeter to terminals 3 and 4
on the connector. Numbers are marked on the connector.
See Fig. 15.
2. Set the meter to 10,000 ohms. The resistance value obtained should be 3,333 ohms. Adjust the potentiometers
and the resistance value should not change.
3. Connect the ohmmeter to terminals 3 and 6. As the reset
limit potentiometer is turned clockwise, resistance should
increase from 0 to approximately 3,400 ohms.
4. Connect the ohmmeter to terminals 3 and 5. As the economizer minimum position potentiometer is turned clockwise, resistance should increase from 0 to approximately
3,400 ohms.
5. Connect the ohmmeter to terminals 3 and 2. As the warm-up
set point potentiometer is turned clockwise, resistance should
increase from 0 to approximately 3,400 ohms.
If any of the Steps 1 through 5 result in any other ohm
reading, replace the board; it cannot be serviced.
TWO-STEP DEMAND LIMIT CONTROL MODULE
(DLCM) TROUBLESHOOTING — If a problem is
suspected in the DLCM board, use the following test
procedure:
The board can only be checked when it is connected to
the processor and the processor is energized so that the DLCM
is supplied with 5 vdc power. The terminals referenced are
shown in Fig. 16. Potentiometers P1 and P2 refer to the DLCM
potentiometers.

TEST

Outdoor-air sensor:
Enthalpy sensor + terminal
should be connected to +
terminal on motor. Connect the
positive terminal of a DC
milliammeter to the S terminal
of the sensor and the negative
terminal of the meter to SO
terminal of the enthalpy board.
Indoor-air sensor:
Enthalpy sensor + terminal
should be connected to +
terminal on motor. Connect the
positive terminal of a DC
milliammeter to the S terminal
of the sensor and the negative
terminal of the meter to SR
terminal of the enthalpy board.

EXPECTED RESULT
AND RESPONSE
Milliammeter reading should be
between 3 and 24 mA if sensor
is operating correctly. If reading
is 0 mA, the sensor is either
wired backwards or is defective.

Milliammeter reading should be
between 3 and 24 mA if sensor
is operating correctly. If reading
is 0 mA, the sensor is either
wired backwards or is defective.

Economizer Motor — All control of the motor (i.e.,
enthalpy changeover, minimum position control and mixed
air control) is accomplished from the main unit microprocessor through a relay board. Service and installation instructions for the unit should be consulted to verify proper operation of these controls. The economizer motor may be checked
out separately. See Fig. 52 for VAV economizer motor connection information.
Motor Test
Apply 24 volt AC power to terminals T1 and T2 of
motor. Connections to motor terminals 2 and 3 must be
disconnected
A Motor Test
Jumper 1 to
2 at motor

A Expected Result and Response
Motor drives open; if not,
replace motor.

B Motor Test
Jumper 1 to
3 at motor

B Expected Result and Response
Motor drives closed; if not,
replace motor.

Variable Frequency Drive
Factory-installed optional VFD is located near the supply fan and motor. During any service work or programming at the VFD, operation of the fan and motor
is not desirable. Either disable the supply fan or install
an accessory VFD remote display.
NOTE: The VFDs (part no. TOSVERT130-E3) are specially
modified for use on Carrier equipment. Some specifications
and control configuration defaults for Carrier applications
will differ from the VFD manufacturer manual included in
the packet. See Table 29 for listing of Carrier-specific default values.
STANDARD TRANSDUCER CONTROL — The VFD monitors and controls duct pressure (DP) via a differential pressure transducer. The pressure transducer is located in the
auxiliary control box (034-048 units) or in the supply fan
compartment (see Fig. 34). The pressure transducer’s low
pressure reference port is connected to the outside of the unit
cabinet by a factory-installed tubing section. The pressure
transducer’s high pressure reference point must be fieldconnected to the duct pressure pick-up (field-supplied and
installed in the supply duct).
The DP transducer monitors the static pressure in the supply duct and provides a 4 to 20 mA signal directly to the
VFD. (Refer to Table 13 for transducer output signal (mA)
for actual duct static pressure.) The internal logic of the VFD
compares this signal representing actual duct pressure to the
user-configured DP set point. The VFD automatically adjusts its output to the supply fan motor to maintain the desired DP set point. When operating with the factory-standard
DP transducer, the internal PID logic of the VFD is enabled.
EXTERNAL SIGNAL CONTROL — If the VFD is to be
controlled by an external control system other than the factory supplied pressure transducer, the internal PID logic function of the VFD must be disabled. To disable the PID
control:
1. Disconnect all power to the unit and the VFD.
2. Install a jumper across S2-CC (see Fig. 53 and 54 for
VFD terminal board connections).
3. Remove factory-supplied cable attached to IV and CC.
4. Remove other end of the same cable from the pressure
sensor.
5. Connect field supplied speed reference (4 to 20mA) across
terminals IV-CC.
6. Disable the supply fan motor operation.
7. Reconnect power to the unit and VFD.
8. Reprogram the VFD to accept an external reference (in
the Utility parameters group [Gr.Ut], set parameter item
Fnod [no.312] = 4).
9. Enable supply fan motor and return power to the unit.
SUPPLY FAN MOTOR OVERLOAD PROTECTION — The
VFD provides operating overload protection for the supply
fan motor. The factory has programmed the VFD overload
function to match the factory-installed motor (motor size and
efficiency). If the supply fan motor is changed from the original factory selection, the overload value may need to be changed
by the service person. Contact your local Carrier representative for assistance in determining the proper overload
setting.
NOTE: Variable frequency drive size is matched to factoryinstalled motor size. Do not increase motor size without also
changing to equivalent VFD size.

LIMIT SWITCHES

CAPACITOR
3
CW
WINDING
(OPEN)
CCW
WINDING
(CLOSE)

ECONOMIZER
MOTOR

T2
BRAKE
WINDING

1
1

CW
2
FEEDBACK
POTENTIOMETER
3

BLU
RED
YEL
AUX. SWITCH

LEGEND
CCW — Counterclockwise
CW — Clockwise

Fig. 52 — Damper Motor Connection Diagram (VAV)

Table 29 — Carrier Default Program Parameter Values
PARAMETER GROUP

SEtP
(Setup)

Gr.F
(Fundamental)

Gr.Fb
(Feedback)

Gr.SF
(Frequency Settings)
Gr.Pn
(Panel Control)

Gr.St
(Terminal Selection)

Gr.Pr
(Protection)

Gr.Ut
(Utility)

PARAMETER
ACC1
DEC1
UL
LL
Luln
P3
F-P3
P4
F-P4
tHr1
StC1
StL1
OLN
tYP
FH
Pt
FbP1
Fbln
GP
Gl
GA
GFS
P1LL
PuL
PuUl
PuLL
Fsor
Sr.n
SrN1

DEFAULT VALUE
60.0 Sec
60.0 Sec
60.0 Hz
10.0 Hz*
1
20%
0.0 Hz
100%
60 Hz
See Table 31
0
110%
1
5*
60 Hz
2
1*
2
.30
2 sec
0
80
10
1
10
10
60 Hz
1* (054-104 only)
0* (054-104 only)

1t
1t0
1t1
1t2
1t3
1t4
UuC
UuCt
ArSt
Cnod
bLSF
Fnod
bLPn

1
0
56
13
3
10
1*
2
3
1*
1* (054-104 only)
2*
1*

*These settings differ from the Toshiba defaults and are required for Carrier applications.
NOTE: To restore original factory settings, change tYP to 6 in Setup mode (SetP). This restores the VFD original factory settings.

P24 RES RR
ST

FM AM CC

R
CC

S4 RCH P24 LOW LOW

If using the VFD display panel, disconnect all power
to the unit and the VFD before entering unit, or use
the accessory remote display module. Disable supply fan
and motor operation before accessing VFD-mounted display module.

IV FP

FLC FLB FLA

When power is first supplied to the VFD, the display automatically starts with the frequency monitor function of its
standard monitor mode. In the frequency monitor function,
the output frequency is displayed. Push the S/P/M (Setup/
Program/Monitor) key to switch to the Mode Selection menu.
Push the S/P/M key again to toggle the display back to the
standard monitor mode.
From the Mode Selection menu, the service person can
view all of the monitored status variables, including up to
four user-selected variables and any trip history in the memory.
Refer to the separate VFD Operation Manual for detailed
instructions on accessing diagnostic information, initiating
troubleshooting, and clearing any trip history.

4-20mA

Fig. 53 — Variable Frequency Drive Terminal Block
(Size 034-048 Units)

P24 RES RR
ST

FM AM CC

R
CC

S4 RCH P24 LOW LOW

IV FP

FLC FLB FLA

Restoring Factory VFD Defaults — The original
factory configuration values are saved in the memory of the
VFD and can be restored by the service person if required.
There are two types of saved file data: Carrier-factory settings (factory programmed settings made to the VFD which
apply specifically to the unit it is installed on) and standard
defaults for general Carrier unit use.
The Carrier-factory settings are maintained as user settings. These can be restored by entering the Setup mode (in
the S/P/M menu) and setting parameter tYP = 6 on the keypad/
display. This will recall the specific factory defaults for this
unit.
Occasionally it may be necessary to restore the VFD defaults to the general Carrier use values. These are stored in
an OPTION ROM (read-only memory chip). However, some
variables may need to be manually changed to match the
specific unit’s factory default settings. To recall the general
Carrier defaults, enter the Setup mode and set parameter
tYP = 3. Refer to Table 30 for items requiring manual
adjustment.

4-20mA

Fig. 54 — Variable Frequency Drive Terminal Block
(Size 054-104 Units)

VFD Operation — When troubleshooting the VFD, check
first that all required conditions for VFD operation are
satisfied.
For the VFD to run, the following conditions must be met
at the VFD:
1. Drive enable jumper is installed from terminals CC-ST
(factory supplied) (see Fig. 53 and 54).
2. Proper rotation jumper is installed at terminals R-CC (reverse rotation, factory supplied) or terminals F-CC (forward rotation, factory supplied).
UNIT SIZES
034-048
054-074
078-104

ROTATION
Reverse
Forward
Forward

Table 30 — Required User Adjusted Defaults
SIZES
All

JUMPER
R-CC
F-CC
F-CC

054-104

3. Emergency stop jumper is installed from terminals S4-CC
(factory supplied).
4. A 4 to 20 mA signal is applied across terminals IV-C (from
pressure transducer, factory supplied).
5. DIP switch SW1 (located on the VFD’s printed circuit
control panel) must be set to ‘‘I’’ (indicating usage of a
4 to 20 mA input signal at terminals ‘‘IV’’).
6. Speed Control (located on the VFD’s keypad/display) set
for ‘‘Remote’’ (press the ‘‘Speed Ctrl’’ button until LED
‘‘Remote’’ is illuminated).
7. Programmed according to Carrier defaults.
8. Duct Pressure set point established by user, or use factory default (30 Hz indicating 2.50-in. wg) (see Table 13).

ITEM
Motor overload settings (see Table 31)
1. Check jumper CC-F
2. Gr.UT/bLSF = 1
3. Gr.SF/Sr.n = 1
4. Gr.SF/SrN1 = 0
5. SEtP/tYP = 5 (Save User Settings)

Table 31 — Motor Overload Settings
UNIT
VOLTAGE
UNIT 48/50 DESIGNATION
Model No.
Position 12
FK,FY, JK,JY
5
5
6
6
6
FKX,FKY,
6
JKX,JKY
6

AND

And
And
And
And
And
And
And

IFM HP
DESIGNATION
Model No.
Position 15
N
Q
A
K
Q
Q
T

tHr1
SETTING
82.0
86.0
80.0
80.0
80.0
80.0
78.0

LEGEND
IFM — Indoor Fan Motor

VFD Operational Status — The VFDs contain extensive self-diagnostic functions which are accessed through
the VFD display panel (located on the front of the VFD or
at a remote location when the accessory remote display package has been installed).

Unit Wiring — A typical wiring schematic is shown in
Fig. 55.
54

LEGEND AND NOTES FOR FIG. 55
ALM
C
CB
CCB
COMP
CH
CR
DPS
DPT
EAT
EC
ECR
EOR
EQUIP
FS
GND
HIR
HPS
HR
HTR
IDC
IDM
IFC
IFCB
IGV
IGVM

—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—

Alarm
Contactor
Circuit Breaker
Control Circuit Breaker
Compressor
Crankcase Heater
Control Relay
Differential Pressure Switch
Discharge Pressure Transducer
Enering-Air Temperature
Enthalpy Control
Economizer Close Relay
Economizer Open Relay
Equipment
Fan Status Switch
Ground
Heat Interlock Relay
High-Pressure Switch
Heater Relay
Heater
Induced Draft Contactor
Induced Draft Motor
Indoor (Evaporator) Fan Contactor
Indoor Fan Circuit Breaker
Inlet Guide Vanes
Inlet Guide Vanes Motor

LAT
LPS
MTR
MV
NC
NO
OFC
OFM
OMR
PCB
PEC
PEDM
PEM
P, PL
RCB
RES
RFC
RFM
SCT
TB
TRAN
U
VFD

—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—

Leaving-Air Temperature
Low-Pressure Switch
Motor
Main Valve
Normally Closed
Normally Open
Outdoor Fan Contactor
Outdoor (Condenser) Fan Motor
Outdoor Motor Relay
Power Exhaust Circuit Breaker
Power Exhaust Contactor
Power Exhaust Damper Motor
Power Exhaust Motor
Plug
Return Fan Circuit Breaker
Resistor
Return Fan Contactror
Return Fan Motor
Saturated Condensing Thermistor
Terminal Block
Transformer
Unloader
Variable Frequence Drive
Field Wiring
Factory Wiring

NOTES:
1. Connect TRAN1 to H4 for 460 v units. Connect to H3 for 230 v
units. If 208/230 v units are run with a 208 v power supply
connect to H2 .
2. Connect TRAN2 to BLK lead for 460 v units. Connect to ORN lead
for 230 v units. If 208/230 v units are run with a 208 v power supply connect to RED lead.
3. Circuit breaker must trip amps are equal to or less than 156% FLA
(full load amps) for CB1 and CB2. All others are 140%.
4. If any of the original wire furnished must be replaced, it must be
replaced with type 90° C wire or its equivalent.
5. Number(s) indicates the line location of contacts. A bracket over
(2) numbers signifies single pole double throw contacts. An underlined number signifies a normally closed contact. Plain numbers (no lines), signify a normally opened contact.
6. Condenser fan motors are thermally protected.
7. Three phase motors are protected under primary single phasing
conditions.

Fig. 55 — Typical Wiring Schematic; 48FK,JK and 50FK,FY,JK,JY Units (054-074 Shown)

Fig. 55 — Typical Wiring Schematic; 48FK,JK and 50FK,FY,JK,JY Units (054-074 Shown) (cont)

SERVICE TRAINING
Packaged Service Training programs are an excellent way to increase your knowledge of the equipment discussed in this manual, including:
• Unit Familiarization
• Installation Overview

• Maintenance
• Operating Sequence

A large selection of product, theory, and skills programs are available, using popular video-based formats and materials. All include video and/or slides, plus companion book.
Classroom Service Training which includes ‘‘hands-on’’ experience with the products in our labs can
mean increased confidence that really pays dividends in faster troubleshooting and fewer callbacks.
Course descriptions and schedules are in our catalog.
CALL FOR FREE CATALOG 1-800-962-9212
[

] Packaged Service Training

[

] Classroom Service Training

Copyright 1999 Carrier Corporation
Manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice and without incurring obligations.
Book 1 1
PC 111
Catalog No. 534-716
Printed in U.S.A.
Form 48/50F,J-1T
Pg 58
4-99
Replaces: 48/50D,F,J-1T
Tab 1a 1b

START-UP CHECKLIST
MODEL NO.:

SERIAL NO.:

DATE:

TECHNICIAN:

I. PRE-START-UP:
M
M
M
M

VERIFY THAT UNIT IS LEVEL
VERIFY THAT ALL PACKING MATERIALS HAVE BEEN REMOVED FROM UNIT
LOOSEN ALL SHIPPING HOLDDOWN BOLTS AND REMOVE SHIPPING BRACKETS PER INSTRUCTIONS
VERIFY THAT COMPRESSOR SUSPENSION SPRINGS HAVE BEEN LOOSENED PER INSTRUCTIONS

M
M
M
M
M
M
M

VERIFY OPENING OF ECONOMIZER HOODS
VERIFY INSTALLATION OF EXHAUST HOODS
CONFIRM THAT TUBING FOR SPACE AND SUPPLY DUCT PRESSURES HAS BEEN INSTALLED
VERIFY THAT CONDENSATE CONNECTION IS INSTALLED PER INSTRUCTIONS
VERIFY THAT POWER SUPPLY MATCHES UNIT DATA PLATE
VERIFY THAT ALL ELECTRICAL CONNECTIONS AND TERMINALS ARE TIGHT
CHECK GAS PIPING FOR LEAKS (48FK,JK ONLY)

M CHECK THAT INDOOR-AIR FILTERS ARE CLEAN AND IN PLACE
M CHECK FAN WHEEL AND PROPELLER FOR LOCATION IN HOUSING/ORIFICE, AND VERIFY SET SCREWS
ARE TIGHT
M VERIFY THAT FAN SHEAVES ARE ALIGNED AND BELTS ARE PROPERLY TENSIONED
M OPEN SUCTION, DISCHARGE, AND LIQUID LINE SERVICE VALVES
M CHECK COMPRESSOR OIL LEVEL SIGHT GLASS AND VERIFY PROPER LEVEL
M VERIFY THAT CRANKCASE HEATERS HAVE BEEN ENERGIZED FOR 24 HOURS
M CHECK VOLTAGE IMBALANCE
LINE-TO-LINE VOLTS:
AB
V
AC
V
BC
V
(AB + AC + BC)/3 = AVERAGE VOLTAGE =
V
MAXIMUM DEVIATION FROM AVERAGE VOLTAGE =
V
VOLTAGE IMBALANCE = 100 X (MAX DEVIATION)/(AVERAGE VOLTAGE) =
IF OVER 2% VOLTAGE IMBALANCE, DO NOT ATTEMPT TO START SYSTEM!
CALL LOCAL POWER COMPANY FOR ASSISTANCE.

II. PRELIMINARY CHECKLIST ITEMS:
CONTROL SETTINGS
M DIP SWITCHES SET TO MATCH INSTALLED ACCESSORIES:
SUPPLY AIR SET POINT RESET (DIP SWITCH NO. 4 ON)
MORNING WARM-UP (DIP SWITCH NO. 4 ON)
DEMAND LIMIT (DIP SWITCH NO. 5 ON)
M SUPPLY AIR SET POINT (P1) SET BETWEEN 45 AND 70 F
M ECONOMIZER MINIMUM POSITION (P5) SET PER PLANS
M SUPPLY AIR SET POINT RESET SETTINGS:
RESET INITIATION TEMPERATURE (P7) (TYPICALLY 68 TO 72 F)
RESET LIMIT TEMPERATURE (P3) (TYPICALLY 60 TO 70 F)
M MORNING WARM-UP TEMPERATURE (TYPICALLY 50 TO 65 F)
M IGV/VFD DUCT PRESSURE SET POINT PER PLANS
M BUILDING PRESSURE (MODULATING POWER EXHAUST) SET PER PLANS
M DEMAND LIMIT SETTINGS PER PLAN:
SINGLE STEP DEMAND LIMIT (P4) SET (TYPICALLY 25 TO 50%)
TWO-STEP DEMAND LIMIT
DLCM-P1 SET (TYPICALLY 50 TO 75%)
DLCM-P2 SET (TYPICALLY 0 TO 25%)
M OCCUPIED/UNOCCUPIED SWITCH INSTALLED PER FIG. 21 (CLOSE TO START UNIT)
CL-1

CHECK EVAPORATOR FAN SPEED AND RECORD.
CHECK CONDENSER FAN SPEED AND RECORD.
AFTER AT LEAST 10 MINUTES RUNNING TIME, RECORD THE FOLLOWING MEASUREMENTS:
COMP A1

COMP A2

COMP B1

COMP B2

ELECTRICAL
EXHAUST FAN AMPS

SUPPLY FAN AMPS
ELECTRIC HEAT AMPS

TEMPERATURES
OUTDOOR-AIR TEMPERATURE

DB (Dry-Bulb)

RETURN-AIR TEMPERATURE

COOLING SUPPLY AIR

WB (Wet-Bulb)

PRESSURES
GAS INLET PRESSURE

IN. WG
IN. WG

STAGE NO. 2

IN. WG

GAS MANIFOLD PRESSURE

STAGE NO. 1

REFRIGERANT SUCTION

CIRCUIT NO. 1

PSIG

CIRCUIT NO. 2

PSIG

REFRIGERANT DISCHARGE

CIRCUIT NO. 1

PSIG

CIRCUIT NO. 2

PSIG

M VERIFY REFRIGERANT CHARGE USING CHARGING CHARTS IN UNIT INSTALLATION INSTRUCTIONS
GENERAL
M ECONOMIZER MINIMUM VENT SETTING TO JOB REQUIREMENTS

IV. NOTES

CUT ALONG DOTTED LINE

OIL PRESSURE
SUCTION PRESSURE
SUCTION LINE TEMP
DISCHARGE PRESSURE
DISCHARGE LINE TEMP
ENTERING CONDENSER AIR TEMP
LEAVING CONDENSER AIR TEMP
EVAP ENTERING AIR DB TEMP
EVAP ENTERING AIR WB TEMP
EVAP LEAVING AIR DB TEMP
EVAP LEAVING AIR WB TEMP
COMPRESSOR AMPS (L1)
COMPRESSOR AMPS (L2)
COMPRESSOR AMPS (L3)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

III. START-UP

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Create Date                     : 1999:06:16 17:21:35Z
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Author                          : Carrier Corporation

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