Service Instructions

SYSTEM OPERATION
77
HEATING
The heating portion of the refrigeration cycle is similar to the
cooling cycle. By energizing the reversing valve solenoid coil, the
flow of the refrigerant is reversed. The indoor coil now becomes
the condenser coil, and the outdoor coil becomes the evaporator
coil.
The check valve at the indoor coil will open by the flow of
refrigerant letting the now condensed liquid refrigerant bypass
the indoor expansion device. The check valve at the outdoor coil
will be forced closed by the refrigerant flow, thereby utilizing the
outdoor expansion device.
The restrictor orifice used with the CA*F, CHPF and CH**FCB coils
will be forced onto a seat when running in the cooling cycle, only
allowing liquid refrigerant to pass through the orifice opening.
In the heating cycle, it will be forced off the seat allowing liquid
to flow around the restrictor. A check valve is not required in this
circuit.
COOLING CYCLE
For legacy room thermostat: When the room thermostat calls for
cool, the contacts of the room thermostat close making termi-
nals 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 completed. Current now flows
through the magnetic holding 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 com-
pressor and condenser fan motors in either low or high stage
depending on the thermostat’s demand. At the same time, con-
tacts 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 on the
“on” position, then the indoor blower would run continuously
rather than cycling with the compressor.
GSZ, ASZ, SSZ, DSZ, and VSZ 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 condi-
tion 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 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 respec-
tively. 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.
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.
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 com-
pressor 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 continuously
rather than cycling with the compressor.
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.