HVACopediaKeepRite · Heat pump · Defrost
Heat pump (Fast #1174185 board): defrost interval, Quiet Shift and speed-up test
What happens, in order
- Defrost thermostat closes at about 32 F and starts the DFT timing; interval choices are 30, 60, 90 and 120 min
- If the thermostat opens before the interval ends, timing resets
- At the end of the interval defrost starts; it ends when the thermostat opens at about 65 F or after 10 minutes
- Quiet Shift (DIP switch 3 ON, factory off): compressor is off 30 s going into defrost and 30 s coming out; fan stays off 40 s extra when returning to heating
- Forced defrost short the speed-up pins for 5 s and release. With the thermostat open a short 30 s defrost runs (Quiet Shift off) or about 1 minute (30 s compressor off, 30 s defrost) with Quiet Shift on
- Thermostat check with timer at 90 min the unit goes into defrost within about 21 s of shorting the speed-up pins; remove the screwdriver as soon as the reversing valve clicks or the control ends the cycle in about 2 s
Timings and thresholds
| Item | Value |
|---|---|
| Defrost interval | 30 / 60 / 90 / 120 min |
| Defrost start | about 32 F coil |
| Defrost end | about 65 F coil |
| Maximum defrost | 10 min |
| Quiet Shift | 30 s compressor off in and out; fan off 40 s extra |
Applies to: KeepRite / ICP / Tempstar / Heil Performance Series split heat pumps (defrost control Fast #1174185)
Models
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Source: KeepRite/ICP/Tempstar/Heil R-410A and R-22 split A/C and HP service manual 421 08 5400 04, 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.