HVACopediaCarrier · Heat pump · Defrost
Variable-speed heat pump: demand defrost with Auto interval
What happens, in order
- Interval is 30, 60 or 90 min, or Auto (default) from the Infinity Touch control; non-communicating systems use the DIP switches. The 90 minute choice drops to 60 below 37 F outdoor
- Auto sets the next interval from the last defrost length: under 5 min gives 90, 5 to 7 min gives 60, over 7 min gives 30
- Board accumulates compressor run time and, as it approaches the interval, checks the coil sensor
- Defrost starts if the coil has been at or below 32 F for 4 minutes in the interval; otherwise the interval timer restarts
- First interval after power-up is 30 min; defrost only runs below the allowed outdoor temperature
- Compressor runs at its defrost speed during the cycle
- Outdoor air above 25 F defrost ends when the coil is above 60 F (minimum 1 min). Outdoor air 25 F or below: ends when the coil is above 45 F (minimum 2 min), or at 10 min maximum
- At the end the outdoor fan starts 10 s before the reversing valve changes over, and aux heat stays on 15 s longer
Timings and thresholds
| Item | Value |
|---|---|
| Interval options | 30 / 60 / 90 min or Auto |
| First interval | 30 min |
| Defrost demand | coil at or below 32 F for 4 min |
| Termination, OAT above 25 F | coil above 60 F, min 1 min |
| Termination, OAT 25 F or less | coil above 45 F, min 2 min |
| Maximum defrost | 10 min |
| Fan lead before reversing valve change | 10 s |
Applies to: Carrier Infinity 25VNA8 variable-speed heat pump and 24VNA9 variable-speed air conditioner
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
- Single-stage communicating heat pump: demand defrost, Auto interval and Quiet Shift-2 · 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 Infinity 25VNA8/24VNA9 variable-speed heat pump and A/C service manual, Time Delays, Defrost, High and Low Pressure Protection. 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.