HVACopediaICP · Heat pump · Defrost
Heat pump: defrost board interval and defrost timers
What happens, in order
- Interval is 30, 60 or 90 min (jumper at the board edge, factory 90 min)
- The interval timer starts when the contactor is energized with 24 V on T1 and the defrost thermostat is closed at about 32 F; it only counts during heat calls
- When the interval ends, the board starts defrost: it runs like cooling, with the outdoor fan off and second-stage (strip) heat on
- A separate 10 minute defrost timer (not adjustable) runs only while defrosting; defrost ends when the thermostat opens at about 65 F or the timer ends
- Back in heating reversing valve shifts back, outdoor fan starts and strip heat drops out
- Test with the defrost thermostat closed, short the SPEEDUP pins; the reversing valve should shift within 1 to 21 s. Remove the short right after it shifts for a short defrost, or hold it more than 2 s after the shift to go straight back to heating
Timings and thresholds
| Item | Value |
|---|---|
| Interval options | 30 / 60 / 90 min |
| Interval factory | 90 min |
| Defrost timer | 10 min fixed |
| Defrost start | about 32 F coil |
| Defrost end | about 65 F coil |
| Reversing valve shift on speed-up | 1 to 21 s |
Applies to: ICP N4H3 heat pump
Models
More ICP heat pump sequences
- Heat pump: heating cycle with supplemental heat · Heating
- Heat pump: cooling cycle · Cooling
Related
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Source: ICP N4H3 heat pump installation instructions (428 01 5103), Defrost Control Board 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.