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7.0 COMPONENTS & CONTROLS
7.1 Demand Defrost
Control
When the thermostat calls for cooling, the demand
defrost control monitors the outdoor ambient
temperature, outdoor coil temperature and the
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cycle is required.
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built into the microprocessor to provide compressor
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The control cycles the compressor off for 30
seconds at the beginning and the end of the
defrost cycle to eliminate the increased compressor
noise caused by rapidly changing system
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Sections 9.1 and 9.2 for diagnostic flash codes and
sensor resistance values at various temperatures.
Defrost Initiation
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[1.7°C] as measured by a good coil sensor,
2. The compressor has operated for at least 34
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35°F [1.7°C] and
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temperature and the outdoor coil temperature
is greater than the calculated difference
determined by the microprocessor.
Defrost Termination
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continue until 14 minutes has elapsed or the coil
temperature has reached the selected termination
temperature. The factory setting is 70°F [21.1°C]
but can be changed to 50°F [10°C], 60°F [15.6°C]
or 80°F [26.7°C] by relocating the jumper on the
control board.
Temperature Sensors
The coil sensor is located on the outdoor coil at
the point fed by the distribution tubes from the
metering device (short 3/8” dia. Tube). The ambient
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sense outdoor temperatures.
If the outdoor ambient sensor fails, the defrost
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initiate a defrost.
Test Mode
The test mode is initiated by momentarily shorting
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heat pump heating call to enter the test mode. In
this mode of operation, the enable temperature
is ignored and all timers are sped up. To initiate
a manual defrost, short and hold the TEST pins.
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to defrost mode after the compressor noise
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has been reached.
Test Sequence of Operation:
1) Provide a heating call to the heat pump.
2) Short test pins to bypass anti-short cycle timer.
(If unit is running, this step is not necessary.)
3) Short test pins and hold them shorted to enter
defrost mode.
4) Release test pins once control exits noise
abatement delay.
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defrost.
6) Unit should return to heating mode.
Troubleshooting Demand Defrost
During the test mode the coil temperature should
be monitored. If the system exits defrost at
approximately the termination temperature, the
control is operating normally.
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temperature sensor resistance, using the
temperature/resistance chart in Section 9.2.
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resistance of the sensor. At 35°F [1.7°C] the
resistance of the sensor should be approximately
30,000 ohms.
Ensure that the coil sensor is properly installed that
it is not loose or touching the cabinet.
High/Low Pressure Control Monitoring
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High Pressure Control –
Provides active
protection in both cooling and heating modes
at all outdoor ambient temperatures. The high
pressure control is an automatic reset type and
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high side pressure drops to approximately 420
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pressure control resets. If the high pressure control
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compressor and outdoor fan operation.
Low Pressure Control –
Provides active
protection in both heating and cooling modes at all
Components
