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Rheem · Heat pump troubleshooting

Heat pump will not defrost / incomplete or excessive defrost

What is going on

Demand defrost is built into the ICC. Defrost starts when coil is below 35°F, compressor has run at least 34 minutes with coil below 35°F and the algorithm calls for it (or after 6 hours of accumulated run time below 35°F coil). Defrost ends at 14 minutes or when coil reaches termination temp (factory 70°F; 50/60/70/80°F via dip switches).

Likely causes

  • No defrost: reversing valve stuck, failed defrost relay, welded reversing valve relay, loose coil sensor/connector
  • Incomplete defrost: wrong termination setting, poor sensor location, thermostat satisfies during defrost, wind on coil
  • Excessive defrost: poor sensor location, low charge, failed ambient sensor (defrost every 34 minutes)

Check in this order

  1. Set thermostat to heat with a call; press SW2 for 1 second to force defrost test mode.
  2. If the unit enters defrost ('d') and comes back out, the control is working.
  3. If not, check the coil sensor clip (top tube fed from the expansion device) and its connector; check for code 83/84.
  4. Check reversing valve shifts and the outdoor fan stops in defrost.
  5. Check termination temperature dip switches.
  6. Check refrigerant charge if defrosts are frequent.
  7. Press SW2 again to end the test.

Applies to: (-)PRL-JEC 2-stage 16 SEER heat pumps: RPRL/UPRL-024JEC, -036JEC, -048JEC, -060JEC

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Source: Rheem (-)PRL-JEC Heat Pump Installation Instructions, 8.0 Demand Defrost Control / 18.5 Defrost Mechanical Checks, p.17-18, 46. Written in our own words; check the manual for your exact model.

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.