32
Components
High/Low Pressure Control Monitoring –
Enhanced Defrost Control Only
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 automatic 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 where
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 automatic 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 approximately 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 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 approximately 40 psig when the low pressure
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
outdoor 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 lockout mode when the outdoor ambient
temperature rises 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 the indoor air handler/furnace
or by shoting 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
Sensor Temperature vs. Resistance Table:
Degrees C
Degrees F
Ohms
-20 -4 96,974
-10 14 55,298
0 32 32,650
10 50 19,903
20 68 12,493
25 77 10,000
30 86 8,056
40 104 5,324
COMPONENTS & CONTROLS
Demand Defrost Control (cont.)
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