Carrier FCM4 - Cleaning or Replacing Refrigerant; Flow-Control Device; Sequence of Operation

FCM4, FEV, FEM4, FJM, FMA4, FSA4, FSM4, FSU4, FVM4, FXM4, REM4, WAH, WAM, WAP, WAX, WBHL: Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
17
A150463
Fig. 13 – 30 & 36 PCB
Limit Switch
Refer to Electric Heater Kit Function and Troubleshooting section of this
manual.
Sequencer
Early EHK2 heater kits include sequencers instead of relays. Refer to
Electric Heater Kit Function and Troubleshooting section of this manual.
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
Later EHK2 heater kits include sequencers instead of relays. Relay coil
is 24V. Check for proper control voltage. Replace relay if faulty.
CLEANING OR REPLACING REFRIGERANT
FLOW-CONTROL DEVICE
FMA4P, WAMA
The FMA4P and WAMA piston can be removed and cleaned if believed
to be plugged. This unit’s piston is unique and replacements are
available from FAST.
The filter drier should be located on the liquid line at the indoor unit to
prevent particulate from plugging the piston.
FMA4X, WAXA
The FMA4X and WAXA fan coils use an R-410A TXV. The TXV’s are
preset at the factory and do not need adjustment for reliable operation.
Reference the outdoor unit instructions to properly charge the unit to the
correct subcooling. For optimal performance, adjust the TXV so that 6º
F of superheat is measured at the outdoor unit’s vapor service valve
when the indoor return air is 80º F DB/67º F WB and outdoor ambient is
82º F DB. To increase superheat turn the TXV adjustment stem
clockwise no more than one rotation at a time. After an adjustment is
made, wait until the superheat temperature has been stable for 15
minutes before making further adjustments.
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. When thermostat is satisfied, its contacts open
de-energizing contactor and blower relay. This stops compressor and
outdoor fan motor. The indoor fan motor will stop after 90-100 seconds
on the FMA4P and 30 or 90 seconds on the FMA4X.
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.
When thermostat is satisfied, its contacts open de-energizing contactor
and blower relay. This stops compressor and outdoor fan motor. The
indoor fan motor will stop after 90-100 seconds on the FMA4P and 30 or
90 seconds on the FMA4X.
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 outdoor fan
motor.
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 should stop. The indoor fan motor will stop
after 90-100 seconds on the FMA4P and 30 or 90 seconds on the
FMA4X.