HVACopediaRheem · Heat pump · Defrost
Demand defrost cycle
What happens, in order
- In heat mode the ICC watches outdoor coil temperature, ambient temperature and compressor run time
- Defrost starts when the coil is below 35 F, the compressor has run at least 34 minutes with the coil below 35 F, and the algorithm decides a defrost is needed
- A defrost is also forced after 6 hours of accumulated compressor run time with no defrost and the coil below 35 F
- Display shows lowercase d during defrost
- Low pressure control is ignored while defrost runs
- Defrost ends when the coil reaches the terminate temperature or 14 minutes have passed, whichever comes first
- Optional noise abatement compressor shuts down for 5 s going into and coming out of defrost (set by communicating thermostat or service tool)
- If the ambient sensor fails the ICC starts a defrost every 34 minutes of heating with the coil below 35 F
- Test press SW2 for 1 s while running in heat; unit defrosts until termination temperature or 14 min; press SW2 again to end the test
Timings and thresholds
| Item | Value |
|---|---|
| Coil temperature to allow defrost | below 35 F |
| Compressor run before defrost | 34 min |
| Forced defrost run time | 6 hours |
| Max defrost time | 14 min |
| Terminate temperature (default) | 70 F (50, 60, 70 or 80 by dip switch) |
| Ambient sensor failed interval | 34 min |
| Noise abatement pause | 5 s |
Codes you may see during this
d (display)
Applies to: Rheem PRL-JEC heat pump
Models
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Source: PRL-JEC heat pump installation instructions, section 8 Demand 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.