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DEFROST TERMINATION
Once a defrost is initiated, the defrost will continue until fourteen minutes has
elapsed or the coil temperature has reached the terminate temperature. The termi-
nate temperature is factory set at 70°F, although the temperature can be changed
to 50°F, 60°F, 70°F or 80°F by relocating a jumper on the board.
TEMPERATURE SENSORS
The coil sensor is clipped to the outdoor coil. The air sensor is located in the out-
door coil compartment.
If the ambient sensor fails the defrost control will initiate a defrost every 34 minutes
with the coil temperature below 35°F.
If the coil sensor fails the defrost control will not initiate a defrost.
TEST MODE
The test mode is initiated by shorting the TEST pins. In this mode of operation, the
enable temperature is ignored and all timers are sped up by a factor of 240. To initi-
ate a manual defrost, short the TEST pins. Remove the short when the system
switches to defrost mode. The defrost will terminate on time (14 minutes) or when
the termination temperature has been achieved. Short TEST pins again to terminate
the defrost immediately.
TROUBLE SHOOTING DEMAND DEFROST
Set the indoor thermostat select switch to heat and initiate a call for heat.
Jumper the "test pins" to put the unit into defrost. If the unit goes into defrost and
comes back out of defrost, the indication is that the control is working properly.
If the unit did not go into defrost using the test pins, check to ensure that 24V is
being supplied to the control board. If 24V is present then replace the control.
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.
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