HVACopediaCarrier · Heat pump · Defrost
Single-stage communicating heat pump: demand defrost, Auto interval and Quiet Shift-2
What happens, in order
- Defrost interval is 30, 60, 90 or 120 min (DIP switches, or the Infinity control which overrides them); Auto adjusts it from the last defrost time
- Last defrost under 3 min sets the next interval to 120 min; 3 to 5 min sets 90; 5 to 7 min sets 60; over 7 min sets 30
- Board adds up compressor run time and looks at the coil sensor as it nears the interval
- A defrost is needed if the coil is at or below 32 F for 4 minutes during the interval; if the coil never gets that cold the interval timer resets
- First interval after power-up is 30 min, and defrost only runs when outdoor air is below 50 F
- Defrost ends when the coil reaches 65 F or after 10 minutes
- Quiet Shift-2 at start the compressor is off 70 s with the reversing valve energized, then the compressor restarts and the fan turns off; at the end the fan comes on shortly before a 60 s compressor-off, with the reversing valve de-energized during that off period
- Non-communicating hold if the thermostat is satisfied mid-defrost, the control holds in defrost and finishes it on the next heat call
- Forced defrost short the pins for 5 s. A full cycle happens only if the coil is at 32 F and outdoor air is under 50 F; otherwise only a 30 s defrost runs
Timings and thresholds
| Item | Value |
|---|---|
| Interval options | 30 / 60 / 90 / 120 min |
| First interval after power-up | 30 min |
| Defrost demand | coil at or below 32 F for 4 min |
| Defrost allowed below | 50 F outdoor |
| Defrost end | 65 F coil or 10 min |
| Quiet Shift-2 | 70 s off at start, 60 s off at end |
Applies to: Carrier / Bryant / Payne split heat pumps with HK32EA defrost control boards (Performance Series and Comfort Series)
Models
More Carrier heat pump sequences
- Single-stage communicating heat pump: time delays and operating functions · Startup
- 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
- 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.