GPCH3 Installation Manual
10
When the solenoid valve coil is operated either from heating
to cooling or vice versa, the piston in the reversing valve
reversing valve.
Figure 7 shows a schematic of a heat pump on the cooling
cycle and the heating cycle. In addition to a reversing valve,
a heat pump is equipped with an expansion device and
check valve for the indoor coil, and similar equipment for the
outdoor coil. It is also provided with a defrost control system.
the same function on the heating cycle as on the cooling
When the heat pump is on the heating cycle, the outdoor
coil is functioning as an evaporator. The temperature of the
refrigerant in the outdoor coil must be below the temperature
of the outdoor air in order to extract heat from the air. Thus,
outdoor coil temperature, the greater the heating capacity of
the heat pump. This phenomenon is a characteristic of a heat
pump. It is a good practice to provide supplementary heat for
all heat pump installations in areas where the temperature
drops below 45° F. It is also a good practice to provide
requirement should there be a component failure of the heat
pump, such as a compressor, or refrigerant leak, etc.
Since the temperature of the liquid refrigerant in the outdoor
coil on the heating cycle is generally below freezing point,
frost forms on the surfaces of the outdoor coil under
certain weather conditions of temperature and relative
the refrigerant to provide hot gas in the outdoor coil to melt
the frost accumulation. This is accomplished by reversing
the heat pump to the cooling cycle. At the same time, the
outdoor fan stops to hasten the temperature rise of the
outdoor coil and lessen the time required for defrosting.
The indoor blower continues to run and the supplementary
heaters are energized.
During operation the power to the circuit board is controlled
by a temperature sensor, which is clamped to a feeder tube
entering the outdoor coil. Defrost timing periods of 30,60
and 90 minutes may be selected by setting the circuit board
jumper to 30, 60 and 90 respectively. Accumulation of time
for the timing period selected starts when the sensor closes
calls for heat. At the end of the timing period, the unit’s
defrost cycle will be initiated provided the sensor remains
defrost cycle is terminated and the timing period is reset.
If the defrost cycle is not terminated due to the sensor
temperature, a twelve minute override interrupts the unit’s
defrost period.
1.
2. Check unit for proper charge.
on the condenser coil indicate low refrigerant charge.
3.
4. Disconnect outdoor fan by removing the outdoor fan
motor wire from “DF2” on defrost control.
5. Restart unit and allow frost to accumulate.
6. After a few minutes of operation, the unit’s defrost
thermostat should close. To verify this, check for
24 volts between “DFT” and “C” on board. If the
temperature at the thermostat is less than 28° F and
the thermostat is open, replace the unit’s defrost
thermostat, as it is defective.
7. When the unit’s defrost thermostat has closed, short
the test pins on the defrost board until the reversing
valve shifts, indicating defrost. This should take up
to 22 seconds depending on what timing period the
control is set on. After defrost initiation, the short must
instantly be removed or the unit’s defrost period will
only last 3 seconds.
8. The control is shipped from the factory with the
compressor delay option selected. This will de-energize
the compressor contactor for 30 seconds on defrost
initiation and defrost termination. If the jumper is set
to Normal, the compressor will continue to run during
defrost initiation and defrost termination. The control
will also ignore the low pressure switch connected to
R-PS1 and PS2 for 5 minutes upon defrost initiation
and 5 minutes after defrost termination.
9. After the unit’s defrost thermostat has terminated,
check the defrost thermostat for 24 volts between
“DFT” and “C”. The reading should indicate 0 volts
10.
11. Replace outdoor fan motor lead to terminal “DF2” on
defrost board and turn on power.
measurements and adjustments. Unit’s blower curves
are considered internal static pressure, so as long as ESP
is maintained, the unit will deliver the proper air up to the
maximum static pressure listed for the CFM required by the