The time delay is 5 minutes long. The delay helps to protect the
compressor from short cycling in case the power to the heat
pump is interrupted or a pressure switch opens. The delay is
bypassed by placing the timer select jumper across the TEST
pins for 0.5 seconds.
Pressure Switch Circuit
The defrost control includes LO-PS terminals to connect an
optional low pressure (loss of charge pressure) switch. A high
pressure switch (optional) can be connected to the HI PS
terminals. See "Defrost Control Board" in the "Adjust Defrost
During a single demand cycle, the defrost control will lock out
the heat pump after the fifth time that the circuit is interrupted by
any pressure switch wired to the control board. In addition,
the diagnostic LEDs will indicate a locked-out pressure switch
after the fifth occurrence of an open pressure switch. See
Defrost Control Board Diagnostic LEDs chart later in this section.
The heat pump will remain locked out until power to the board is
interrupted, then re-established, or until the jumper is applied to
the TEST pins for 0.5 seconds.
NOTE: The defrost control board ignores input from the low
pressure switch terminals during:
90-second start-up period
First 90 seconds after the reversing valve switches heat/cool
NOTE: If the TEST pins are jumpered and the 5-minute delay is
being bypassed, the LO PS terminal signal is not ignored during
the 90-second start-up period.
Defrost Control Board Diagnostic LEDs
No Power to Board
Normal Operation/Power to Board
Short Cycle Lockout
Low Pressure Switch Fault
Low Pressure Switch Lockout
High Pressure Switch Fault
High Pressure Switch Lockout
Simultaneous Slow Flash
Alternating Slow Flash
Adjust Defrost System
Defrost Control Board
Optional high pressure switch connections
NOTE: To add the pressure switch, remove the factory-installed
A. Defrost time setting pins
B. Test pins
C. Compressor delay pins
D. Reversing valve
E. Low pressure switch (optional)
Adjust Time Between Defrost Cycles
Electrical Shock Hazard
Disconnect power before servicing.
Replace all parts and panels before operating.
Failure to do so can result in death or electrical shock.
1. Disconnect power.
TST PS DF C
R O Y1
F. Defrost thermostat
G. High pressure switch (optional)
H. Diagnostic LEDs
I. Low voltage terminal strip