HVACopediaCarrier · Heat pump · Startup
Variable-speed unit: power-up and compressor time delays
What happens, in order
- On every high-voltage power-up the control holds a 10 minute sump warm-up delay
- After the last cycle, power-up or a brown-out the compressor waits 3.5 minutes before running; shorting and releasing the forced defrost pins bypasses this wait
- At the end of each compressor run the pressure equalizer valve (PEV) opens for 150 s, then is closed for 15 s before the next compressor start; this delay cannot be bypassed
- Crankcase heater is managed by the control and works whenever the outdoor unit has power, even with no indoor unit connected; the compressor windings are also pulsed now and then during long off cycles to keep the sump warm
- Brown-out if line voltage stays under 187 V for 4 s the compressor and fan stop; they cannot run again until voltage is at least 190 V
- Control drops to standby 2 minutes after the last valid communication
Timings and thresholds
| Item | Value |
|---|---|
| Sump warm-up at power-up | 10 min |
| Compressor delay | 3.5 min |
| PEV open after run | 150 s |
| PEV closed before next start | 15 s |
| Aux heat off delay after defrost | 15 s |
| Brown-out cutout | below 187 V for 4 s |
| Brown-out recover | 190 V |
Codes you may see during this
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
- 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 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.