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8.6 HIGH/LOW PRESSURE CONTROL MONITORING - ENHANCED
DEFROST CONTROL ONLY (Units with Model Numbers Ending with "AZ")
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 440 psig and closes at approximately
270 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 270 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 7 psig and closes at approximately 22
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 22 psig and the low pressure control automatically resets. If the low
pressure switch open 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 pres-
sure control opens and will start again when the low side pressure rises to
approximately 22 psig and the low pressure control automatically resets. If the
low pressure switch trips 3 times within 120 minutes of operation during a par-
ticular call for heating operation, the defrost control will lock out compessor 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
lock-out mode when the outdoor ambient temperature rises to 5°F. This fea-
ture is necessary since the low pressure control could possibly have opened
due to the outdoor ambient being very low rather than an actural 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 shorting the two
defrost control test pins together.
8.7 ENHANCED FEATURE DEFROST CONTROL DIAGNOSTIC CODES
LED 1
LED 2
OFF
OFF
ON
ON
OFF
ON
FLASH
FLASH
OFF
FLASH
FLASH
OFF
ON
FLASH
FLASH
ON
Alternate Flashing
9.0 EVACUATION PROCEDURE
The life and efficiency of the equipment is dependent upon the thoroughness exer-
cised by the technician when evacuating air and moisture from the system.
Air in the system causes high condensing temperatures and pressure, resulting in
increased power input and non-verifiable performance.
Moisture chemically reacts with the refrigerant and oil to form corrosive hydrofluoric
and hydrochloric acids. These attack motor windings and parts, causing breakdown.
Control Board Status
No Power
Coil Sensor Failure
Ambient Sensor Failure
Normal
Low Pressure Lockout (short test pins to reset)
High Pressure Lockout (short test pins to reset)
Low Pressure Control Open
High Pressure Control Open
5 Minute Time Delay
15
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Troubleshooting
