HVACopediaKeepRite · Heat pump · Defrost
Heat pump: time/temperature defrost and Quiet Shift 2
What happens, in order
- Defrost interval is 30, 60, 90 or 120 min (quick connects on older boards, DIP switches on Quiet Shift 2 boards); on HK32EA011 and later aluminum-coil boards this is the first interval only and later intervals vary with defrost length
- Defrost thermostat closes at about 32 F; the timer runs only while the thermostat is closed and the contactor is energized
- In defrost the unit runs as in cooling except the outdoor fan is off and second-stage heat comes on
- Defrost ends when the thermostat opens at about 65 F, or after 10 minutes
- Quiet Shift 2 (DIP switch 3 ON, aluminum coil units): at start the compressor is off about 1 minute, then the reversing valve energizes, a few seconds later the compressor restarts and normal defrost runs; at the end the compressor is off about 1 minute again before the reversing valve de-energizes and the compressor returns to heating
- On HK32EA012 and later boards, Quiet Shift 2 turns off variable intervals so the DIP switch interval stays until the switch is changed and power cycled; a forced defrost resets the interval to the DIP setting
- Forced defrost on Quiet Shift 2 boards short the J1 speed-up pins for 5 s and release. With the thermostat open only a 30 s defrost occurs (Quiet Shift off) or a roughly 3 minute sequence (1 min compressor off, 30 s defrost, 1 min off) with it on
- Other boards close the defrost thermostat (cut power, disconnect outdoor fan from OF2/ODF, restart in heat until frost builds), short the speed-up pins (timing reduced to 1/25) and remove the short as soon as the reversing valve changes; the unit stays in defrost until the thermostat opens at about 65 F or the 10 minute timer ends
Timings and thresholds
| Item | Value |
|---|---|
| Defrost interval | 30 / 60 / 90 / 120 min |
| Defrost start | about 32 F coil |
| Defrost end | about 65 F coil |
| Maximum defrost | 10 min |
| Quiet Shift 2 compressor-off | about 1 min at start and 1 min at end |
| Forced defrost pin hold | 5 s |
Applies to: KeepRite / ICP N4H4, R4H4, WCH4, NXH5 heat pumps
Models
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Source: KeepRite/ICP N4H4-R4H4-WCH4-NXH5 heat pump installation instructions 428 01 5107 10, Defrost and Sequence of Operation. Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
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.