CAPF R-410A Service Manual

SYSTEM OPERATION
62
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.
If room thermostat fan status is set to be “on”, then indoor
blower would run continuously rather than cycling with the
compressor.
For heat pumps, the reversing valve is energized during a
cooling a cycle. The call for cooling from the communicating
thermostat indicates to the control that the reversing valve is
to be energized during cooling operation.
DEFROST CYCLE - LEGACY MODELS
The defrosting of the outdoor coil is jointly controlled by the
defrost control board and the defrost thermostat.
Solid State Defrost Control
During operation the power to the circuit board is controlled
by a temperature sensor, which is clamped to a return bend
(3/8" coils) or a feeder tube (5 mm coils) entering the outdoor
coil. Defrost timing periods of 30, 60, or 90 minutes may be
selected by connecting the circuit board jumper to 30, 60, or
90 respectively. Accumulation of time for the timing period
selected starts when the sensor closes (approximately 31°
F), and when the room thermostat calls for heat. At the end
of the timing period, the unit’s defrost cycle will be initiated
provided the sensor remains closed. When the sensor opens
(approximately 75° F), the defrost cycle is terminated and the
timing period is reset. If the defrost cycle is not terminated
due to the sensor temperature, a ten minute override inter-
rupts the unit’s defrost period. The new upgraded defrost
control has a 12 minute override interrupt.
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 the microprocessor on the UC checks
coil temperature via the OCT sensor every 30, 60, 90, or 120
minutes when there is a call for heating. If by the time the
microprocessor checks the coil temperature, and it's low
enough (approximately 31°F), and if there is a call for heat
from the thermostat, the PCB will initiate a defrost. When the
microprocessor detects the coil temperature to be high
enough (approximately 75
0
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 “RECALL” button on the UC board.
HEATING CYCLE
The reversing valve on the GSZ, SSZ, ASZ and DSZ models
is energized in the cooling cycle through the "O" terminal on
the room thermostat.
These models have a 24 volt reversing valve coil. When the
thermostat selector switch is set in the cooling position, the
"O" terminal on the thermostat is energized all the time.
Care must be taken when selecting a room thermostat. Refer
to the installation instructions shipped with the product for
approved thermostats.
HEATING CYCLE
For legacy room thermostat: When the room thermostat
calls for heat, the contacts of the room thermostat close
making terminals R to Y & G, the low voltage circuit of the
transformer is completed. Current now flows through the
magnetic holding coils of the compressor contactor (CC) and
fan relay (RFC).
This draws in the normally open contact CC, starting the
compressor condenser fan motors. At the same time,
contacts RFC close, starting the indoor fan motor.
When the thermostat is satisfied, it opens its contacts,
breaking the low voltage circuit, causing the compressor
contactor and indoor fan relay to open, shutting down the
system.
If the room thermostat fan selector switch should be set to
the “on” position, then the indoor blower would run continu-
ously rather than cycling with the compressor.
For communicating room thermostat: When the room ther-
mostat calls for either low stage heat or high stage heat,
appropriate commands are sent via the data 1 and data 2
lines to the outdoor unit's UC control. The UC control
energizes the on-board compressor relay and the on-board
outdoor fan relay. The compressor high stage solenoid is
energized if it is a high stage call. The UC control sends a
fan command to the indoor unit (air handler or furnace). The
indoor unit operates the indoor blower at the appropriate
airflow level. The system operates at the cooling level
demanded by the thermostat.