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Goodman · Heat pump troubleshooting

Outdoor coil iced / no defrost - R-32 GLZS/ALZS heat pump

What is going on

Outdoor coil builds ice in heating and the unit does not go into defrost, or defrost does not end properly.

Likely causes

  • Defrost thermostat not closing or mounted badly
  • Defrost control board fault
  • Reversing valve or outdoor fan relay problem

Check in this order

  1. With power on and the unit idle, jumper DFT to R (R-DFT) on the defrost board.
  2. Move the timer jumper to the TEST pins (use the proper jumper, not a screwdriver), call for heat - the unit should enter defrost within 21 seconds; then remove the test jumper at once.
  3. In defrost check 24 V across C and O; line voltage (208-230 VAC) across DF1 and DF2 (fan relay open); 24 V across W/W2 and C.
  4. If any reading is wrong, replace the defrost board.
  5. Test the defrost thermostat with a thermocouple on the adjacent tube: closing and opening temperatures depend on the part (see Specs tab).
  6. Power off, remove the DFT jumper and put the timer jumper back on the chosen 30/60/90 minute pins before leaving.

Applies to: R-32 GLZS4/5 and ALZS4/5 heat pumps

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Source: Goodman RS6200301 R-32 GLXS/ALXS/GLZS/ALZS service (07-2024), Testing Defrost Control / Defrost Thermostat p.32-33. 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.