HVACopediaCarrier · Heat pump · Defrost
Non-communicating heat pump: time/temperature defrost and Quiet Shift
What happens, in order
- Defrost thermostat on the coil closes at about 32 F, energizing the DFT terminal and starting the interval timer
- If the thermostat opens again before the timer ends, the timer resets
- When the timer reaches the selected interval (30, 60 or 90 min on 001/007; 30, 60, 90 or 120 min on 003/008), defrost starts
- Control shifts the reversing valve to cooling position and stops the outdoor fan; hot gas melts the frost
- Defrost ends when the defrost thermostat opens at about 65 F, or after 10 minutes, whichever comes first
- Quiet Shift (003/008, DIP switch 3 ON) compressor goes off for 30 s going into defrost and again for 30 s coming out; fan stays off an extra 40 s on return to heating
- Forced defrost short the speed-up pins for 5 s and release. With the defrost thermostat open you get a short 30 s defrost (Quiet Shift off) or a 1 min test (30 s compressor-off then 30 s defrost) with Quiet Shift on
- On 001/007 boards the speed-up pins make the timer 256 times faster; the unit changes over within about 21 s and the screwdriver must be removed as soon as the reversing valve clicks, or defrost ends in about 2 s
Timings and thresholds
| Item | Value |
|---|---|
| Defrost interval | 30 / 60 / 90 min (001/007); 30 / 60 / 90 / 120 min (003/008) |
| Defrost start temperature | about 32 F coil |
| Defrost end temperature | about 65 F coil |
| Maximum defrost length | 10 min |
| Quiet Shift compressor-off | 30 s in and 30 s out |
| Fan off after defrost (Quiet Shift) | 40 s |
| Forced defrost pin hold | 5 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
- 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
- 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.