HIGH/LOW PRESSURE CONTROL MONITORING - ENHANCED
DEFROST CONTROL
Status of high and low pressure controls is monitored by the enhanced feature
demand defrost control and the following actions are taken.
High Pressure Control – Provides active protection in both cooling and heating
modes at all outdoor ambient temperatures. The high pressure control is an auto-
matic reset type and opens at approximately 610 psig and closes at approximately
420 psig. The compressor and fan motor will stop when the high pressure control
opens and will start again if the high side pressure drops to approximately 420 psig
when the automatic reset high pressure control resets. If the high pressure control
opens 3 times within a particular call for heating or cooling operation, the defrost
control will lock out compressor and outdoor fan operation.
Low Pressure Control – Provides active protection in both heating and cooling
modes at all outdoor ambient temperatures. The low pressure control is an auto-
matic reset type and opens at approximately 15 psig and closes at approximately
40 psig. Operation is slightly different between cooling and heating modes.
Cooling Mode: The compressor and fan motor will stop when the low pressure
control opens and will start again when the low side pressure rises to approxi-
mately 40 psig when the low pressure control automatically resets. If the low
pressure switch opens 3 times within a particular call for cooling operation, the
defrost control will lock out compressor and outdoor fan operation.
Heating Mode: The compressor and fan motor will stop when the low pressure
control opens and will start again when the low side pressure rises to approxi-
mately 40 psig when the low pressure control automatically resets. If the low
pressure switch trips 3 times within 120 minutes of operation during a particular
call for heating operation, the defrost control will lock out compressor and out-
door fan operation. If the lock-out due to low pressure occurs at an outdoor
ambient temperature below 5°F, the defrost control will automatically exit the
lock-out mode when the outdoor ambient temperature rises to 5°F. This feature
is necessary since the low pressure control could possibly have opened due to
the outdoor ambient being very low rather than an actual system fault.
Exiting Lock-Out Mode: To exit the lock-out mode, remove 24 volts to the defrost
control by removing power to indoor air-handler/furnace or by shorting the two
defrost control test pins together.
ENHANCED FEATURE DEFROST CONTROL DIAGNOSTIC CODES
LED 1 LED 2 Control Board Status
OFF OFF No Power
ON ON Coil Sensor Failure
OFF ON Ambient Sensor Failure
FLASH FLASH Normal
OFF FLASH Low Pressure Lockout (short test pins to reset)
FLASH OFF High Pressure Lockout (short test pins to reset)
ON FLASH Low Pressure Control Open
FLASH ON High Pressure Control Open
Alternate Flashing 5 Minute Time Delay
15
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