HVACopediaKeepRite · Heat pump troubleshooting
Forcing a defrost to test the board - KeepRite N4H4/R4H4/WCH4/NXH5
What is going on
Steps to force a defrost cycle and confirm the defrost board, thermostat and reversing valve work.
Likely causes
- Defrost thermostat stuck open or closed
- Defrost board fault
- Reversing valve not shifting
Check in this order
- Quiet Shift-2 boards short the J1 speed-up pins for 5 s and release. With the defrost thermostat open you only get a short test defrost; with it closed a full defrost starts.
- Other boards power off, unplug the outdoor fan lead (OF2 on PSC units, ODF on ECM units) and tape it.
- Run in heat until the liquid line drops below about 30°F so the defrost thermostat closes.
- Short the speed-up terminals; release the moment the reversing valve shifts, or the 10-minute defrost is skipped in about 2 s.
- Defrost should end when the coil/liquid line reaches about 65°F or when time runs out.
- Power off and reconnect the fan lead when done.
Applies to: KeepRite N4H4, R4H4, WCH4, NXH5 heat pumps
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Source: KeepRite/ICP N4H4/R4H4/WCH4/NXH5 Installation Instructions 428 01 5107 10, Defrost / Defrost Speedup p.7-8. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.