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FCM4, FEV, FEM4, FJM, FMA4, FSA4, FSM4, FSU4, FVM4, FXM4, REM4, WAH, WAM, WAP, WAX, WBHL: Service and Maintenance Instructions
FAN COIL DESCRIPTION and
TROUBLESHOOTING
PSC FAN MOTOR
FSM4, FSU4, FSA4
The PSC motor is two or three speed direct drive. High-speed lead is
black, low-speed lead is red, and common lead is yellow. Be sure proper
blower speed has been selected..
The motor is turned on through two different routes. The first occurs
when thermostat calls for the fan in cooling, heat pump, or fan-only
mode. A 24VAC signal is sent to relay, causing relay to close its
normally open contacts, turning fan on.
The second occurs when there is a call for electric heat. A 24VAC signal
is sent to heater sequencer/relay, causing it to close, directing 230V
through the normally closed contact of fan relay, turning fan on. The fan
remains on until sequencer/relay opens.
If motor does not run, test motor for an open winding or a winding
shorted to motor case. If either is present, replace motor.
ELECTRIC HEATER SERVICE
Service can be completed with heater in place. Shut off power before
servicing.
LIMIT SWITCH
Refer to
Electric heater function and troubleshooting on pg
SEQUENCER
Refer to
Electric heater function and troubleshooting on pg
TRANSFORMER
A 40VA transformer supplies 24V power for control circuit. Check for
208/230V on primary side of transformer. If present, check for 24V on
secondary side.
NOTE: Transformer is fused. Do not short circuit.
FAN RELAY
Relay coil is 24V. Check for proper control voltage. Replace relay if
faulty.
CLEANING OR REPLACING REFRIGERANT
FLOW-CONTROL DEVICE
Refer to
Fig. 22
and instructions in
Replacement on pg
25.
The refrigerant flow-control device is protected by a wire mesh strainer.
It is located inside the 3/8-in. liquid tube at field braze joint next to
flow-control device. Access to strainer is through field braze joint.
SEQUENCE OF OPERATION
Condensing Unit
COOLING
When thermostat calls for cooling, the circuit between R and G is
complete and single-pole single-throw relay FR is energized. The
normally open contacts close causing blower to operate.
The circuit between R and Y is also complete. This completed circuit
causes contactor in outdoor unit to close which starts compressor and
outdoor fan.
HEATING
When thermostat calls for heating and FAN switch is set on AUTO, the
circuit between R and W is complete. The heater sequence SEQ is
energized which closes contacts of relay. There will be a time delay. This
completed circuit energizes all heating elements HTR and blower motor.
Heat Pump
COOLING
On a call for cooling, the thermostat makes circuits R-O, R-Y, and R-G.
Circuit R-O energizes reversing valve, switching it to cooling position.
Circuit R-Y energizes contactor starting outdoor fan motor and
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
15.
15.
Piston Body Cleaning and
compressor. Circuit R-G energizes indoor unit blower relay starting
indoor blower motor.
When thermostat is satisfied, its contacts open de-energizing contactor
reversing valve and blower relay. This stops compressor and fan motors.
HEATING
On a call for heating, the thermostat makes circuits R-Y and R-G. Circuit
R-Y energizes contactor starting outdoor fan motor and compressor.
Circuit R-G energizes indoor blower relay starting blower motor.
Should temperature continue to fall, R-W circuit is made through
second-stage room thermostat bulb. Circuit R-W energizes a sequencer
bringing on supplemental electric heat.
When thermostat is satisfied, its contacts open de-energizing contactor
and sequencer. All heaters and motors should stop.
Control Board (contact FAST for part number)
This section of the service manual describes the PCB by examining the
functional operation of the PCB components.
Printed Circuit Board (PCB) Component
Layout of the actual PCB is depicted in
1. The low-voltage stripped leads are used to connect the 24V side of
transformer to indoor thermostat and outdoor section.
2. A 5A fuse is used to protect the low-voltage transformer secondary.
3. The fan relay is controlled by thermostat and turns fan on and off.
4. A plug is used as the connection for PCB power and electric
heaters. Note the pin numbers on plug.
5. A time-delay relay circuit keeps fan motor running for
approximately 90 seconds after G is de-energized. The time-delay
can be defeated by cutting jumper JW1.
Unit Functions
TRANSFORMER
1. Proper Wiring of Transformer Primary or High Side—Yellow wire
from Molex plug is wired to C terminal on transformer and black
wire from PCB relay (normally-open) terminal is wired to 208V or
230V terminal on transformer. Units are factory wired at 230V
terminal.
2. Proper Wiring of Transformer Secondary or 24V Side—Red wire
of transformer is wired to T terminal on PCB and brown wire of
transformer is wired to C terminal on PCB.
NOTE: T terminal on PCB is used to protect the transformer. T terminal
is connected through the fuse to R terminal on PCB.
INDOOR FAN
1. Wiring—Indoor fan motor yellow lead is wired to C terminal on
transformer. The red, blue, or black speed lead is wired to SPT
terminal on fan relay part of PCB. Units are factory wired on
medium speed (blue lead connected).
NOTE: Unused fan speed leads must be capped or taped off to prevent
direct short to cabinet surface.
2. Functional Control
a. Thermostat and Relay Control—When thermostat calls for the
fan in cooling, heat pump, heating, or fan-only mode, a 24VAC
signal is sent to relay. This causes the relay to close its normally
open contacts, turning on fan. When thermostat no longer calls
for the fan, the signal sent to relay is turned off and relay opens
causing fan to turn off after a 90-second fan-off delay.
b. Sequencer/Electric Heat Relay Interlock—The fan will also
operate whenever there is a call for electric heat, even if fan relay
is not energized. This happens because fan is interlocked with
first stage of electric heat through the normally-closed contact of
fan relay.
2
Fig.
1.
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Troubleshooting
