GSZH5 Service Manual

59
SYSTEM OPERATION
Cooling Cycle
For legacy room thermostat: When the room thermostat
calls for cool, the contacts of the room thermostat close
making terminals R to Y1 & G (if thermostat calls for low
stage cool), or R to Y1, Y2 & G (if thermostat calls for high
stage cool), the low voltage circuit of the transformer is
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coils of the compressor contactor (CC) and fan relay (RFC).
If thermostat calls for high stage cool, the microprocessor
on the UC board will also energize the compressor high
stage solenoid to run the compressor at full capacity.
This draws in the normally open contact CC, starting the
compressor and condenser fan motors in either low or high
stage depending on the thermostat’s demand. At the same
time, contacts RFC close, starting the indoor fan motor.
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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
on the “on” position, then the indoor blower would run
continuously rather than cycling with the compressor.
GSZ, ANZ, ASZ, SSZ, DSZ, VSZ, GSZH5 and ASZH5
models energize the reversing valve thorough the “O”
circuit in the room thermostat. Therefore, the reversing
valve remains energized as long as the thermostat subbase
is in the cooling position. The only exception to this is
during defrost.
For heat pumps, during cooling cycle the reversing valve is
energized as the room thermostat closes “O” terminal to R
and the microprocessor on the UC board responds to such
a condition by energizing the solenoid coil on the reversing
valve.
Defrost Cycle
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
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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 interrupts the unit’s
defrost period. The new upgraded defrost control has a 12
minute override interrupt.
Indoor
Coil
Accumulator
Bi-Flow
Filter Dryer
Outdoor
Coil
Thermostatic
Expansion
Valve
Check Valve
Reversing Valve
(De-Energized)
Indoor
Coil
Accumulator
Bi-Flow
Filter Dryer
Outdoor
Coil
Thermostatic
Expansion
Valve
Check Valve
Reversing Valve
(Energized)
Cooling Cycle