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Frost/ice on finned evaporator

What is going on

Possible causes and checks for: frost/ice on finned evaporator.

Likely causes

  • Bad defrost timer
  • Bad defrost heater
  • Bad defrost thermostat
  • Also leaky door gasket (rapid buildup)
  • Mullion heater dead

Check in this order

  1. Test timer with test light
  2. Replace heater/stat
  3. Check gaskets
  4. Check evap fan first, then defrost resistance wire electrically

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Source: General HVAC service practice — verify per model. 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.