SYSTEM OPERATION
25
When the thermostat is satisfied, appropriate commands are
sent to the UC control. The compressor relay and outdoor
fan relay is de-energized. The compressor high stage
solenoid is de-energized if it was energized. The UC control
sends an appropriate command to the indoor unit to de-
energize the indoor blower motor.
DEFROST CYCLE - COMFORTNET
TM
MODELS
The defrosting of the outdoor coil is jointly controlled by the
UC PCB and the outdoor coil temperature (OCT) sensor.
The OCT sensor is clamped to a feeder tube entering the
outdoor coil. Defrost timing periods of 30, 60, 90 or 120
minutes may be selected via the dipswitch settings on the UC
PCB. In a communicating system, the defrost timing periods
can also be selected in the communicating thermostat user
menu. During operation, if the coil temperature is low enough
(approximately 31°F), the microporcessor will accumulate
the compressor run time. When the total compressor run time
reaches 30, 60, 90 or 120 minutes, and there is a call for heat,
the PCB will initiate a defrost cycle. When the microproces-
sor detects the coil temperature to be high enough (approxi-
mately 75°F), or 10 minutes of maximum defrost cycle time
has elapsed, whichever occurs first, the defrost cycle is
terminated and the timing period is reset. The field service
personnel can also advance a heat pump to the defrost cycle
by simultaneously pressing the “TEST” button and the “RE-
CALL” button on the UC board.
Use the dipswitches to select defrost time interval (30, 60, 90
or 120 minutes) See chart below