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Carrier · Heat pump troubleshooting

Heat pump will not defrost - HK32EA defrost board

What is going on

Outdoor coil ices up and the unit never shifts into defrost.

Likely causes

  • Defrost thermostat failed or loose on stub tube
  • No 24 V on T1
  • Bad thermostat pigtail or wiring
  • Failed board

Check in this order

  1. Run a forced defrost with the speed-up pins; if it defrosts, the board is fine and the defrost thermostat is suspect.
  2. No defrost on speed-up check 24 V on T1 - it powers the defrost timing.
  3. Test the defrost thermostat with an ohmmeter while frost builds: it should close near 32 F (33-27 F) and open about 60-70 F after defrost.
  4. Confirm the defrost thermostat sits on the bottom-circuit liquid stub tube and the cup material matches the tube.
  5. During defrost check 24 V between C and W2.
  6. Still no defrost unplug the pigtail and jumper the board inputs directly; a bad pigtail is common.

Applies to: Carrier/Bryant heat pumps with HK32EA boards

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Source: Carrier Residential AC & HP Application Guideline and Service Manual 24-25-9SM (text export), Defrost Speedup and Check Defrost Thermostat. 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.