Service Manual

SERVICE AND MAINTENANCE FAN COILS
2 496 08 8001 02
Specifications subject to change without notice.
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 24−Vac 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
24−Vac 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.
A. Limit Switch
Refer to Electric Heater Function and Troubleshooting section
of this manual.
B. Sequencer
Refer to Electric Heater Function and Troubleshooting section
of this manual.
C. Transformer
A 40−VA transformer supplies 24−V 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.
D. Fan Relay
Relay coil is 24−V. Check for proper control voltage. Replace
relay if faulty.
CLEANING OR REPLACING REFRIGERANT
FLOW−CONTROL DEVICE
Refer to Figure 22 and instructions given in “Piston Body
Cleaning or Replacement” section.
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
A. 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.
B. 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 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 Figure 1.
1. The low−voltage stripped leads are used to connect the
24−V side of transformer to indoor thermostat and
outdoor section.
2. A 5−amp 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
A. 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 208−V or 230−V
terminal on transformer. Units are factory wired at
230−V terminal.
2. Proper Wiring of Transformer Secondary or 24−V 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.
B. 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 24−Vac signal is