HVACopediaCarrier · Heat pump · Startup
Single-stage communicating heat pump: time delays and operating functions
What happens, in order
- Cooling call outdoor fan, reversing valve and compressor energize; on satisfied, compressor and fan shut off but the reversing valve stays in cooling until power is removed or a heating call comes
- Heating call outdoor fan and compressor energize with the reversing valve de-energized
- Outdoor fan runs whenever the compressor runs (except in defrost and at times during low-ambient cooling)
- Outdoor fan keeps running 1 min after cooling ends if outdoor air is 100 F or higher
- At the end of defrost the auxiliary heat (W2) stays on 15 s longer and the outdoor fan starts 20 s after defrost ends
- Crankcase heater energizes during the off cycle when outdoor air is below 65 F
- The 5-minute start delay can be bypassed on a non-communicating system by shorting and releasing the forced defrost pins; on a communicating system press the UI fan and up buttons together for about 10 s
Timings and thresholds
| Item | Value |
|---|---|
| Start delay for cooling or heating | 5 min |
| Compressor recycle after brown-out | 5 min |
| Return to standby after last valid communication | 2 min |
| Fan run-on in cooling at 100 F+ outdoor | 1 min |
| W2 off delay after defrost | 15 s |
| Fan on delay after defrost | 20 s |
| Compressor delays with Quiet Shift-2 | 70 s and 60 s |
Applies to: Carrier / Bryant / Payne split heat pumps with HK32EA defrost control boards (Performance Series and Comfort Series)
Models
More Carrier heat pump sequences
- Variable-speed unit: power-up and compressor time delays · Startup
- Non-communicating heat pump: heating cycle (HK32EA001/007 and 003/008) · Heating
- Non-communicating heat pump: cooling with 5-minute compressor delay (HK32EA003/008) · Cooling
- Non-communicating heat pump: time/temperature defrost and Quiet Shift · Defrost
- Single-stage communicating heat pump: demand defrost, Auto interval and Quiet Shift-2 · Defrost
- Variable-speed heat pump: demand defrost with Auto interval · Defrost
- Single-stage communicating heat pump: pressure switch protection and lockout · Other
- Variable-speed unit: high pressure switch protection and lockout · Other
Related
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Source: Carrier-Bryant residential A/C + HP Application Guideline and Service Manual (R-410A, 24-25), System Function and Sequence of Operation, Defrost Control. 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.