A high pressure alarm indicates the controller has received an open signal from the normally closed high pressure switch circuit. Three active alarms within one hour will trigger a compressor lockout to protect the refrigerant circuit. The lockout can be cleared by power cycling the controller.


Possible Cause
Component to Check
Recommended Action
Condenser coil blockage
Condenser coil
Wash/Clean condenser coil. Remove any blockage.
Loose/incorrect alarm wiring
High Pressure Alarm Wiring (see diagram below )
If the high pressure switch is closed but the controller is receiving an open signal between ID4 and IDC1, verify/tighten alarm wiring according to the High Pressure Alarm Wiring diagram.
Condenser fan wiring
Condenser fan wiring (see diagram below)
If condenser fan does not receive power across wires 120 and 400, verify/tighten condenser fan wiring according to the Condenser Fan Wiring diagram.
Faulty condenser fan switch
High pressure switch for condenser fan (HP1)
If high pressure switch for condenser fan does not close properly, replace the switch.
Condenser fan relay (not present in Cat 5 models)
condenser fan cycle relay (KA2 for 2.5/3.5 Ton model, KA1 for 5 Ton model)
If the fan cycling relay does not close when the coil is energized, replace the relay.
High Pressure Alarm Switch defective
High pressure alarm switch (HP)
HP Switch Spec:
R407C: 420/360 ±10psi*
R410A: 600/450 ±10psi
*Some switches intended for outside of CA/AZ areas are 390/330 ±10psi. These switches are labeled 2.7/2.25MPa
If switch is open when high side pressure is in normal range, replace the switch
Condenser fan failure
Power at Condenser fan (240V across wire 120 and wire 400)
If condenser fan receives power but does not run, replace the condenser fan.

Condenser Fan Wiring

High Pressure Alarm Wiring