Ice Buildup Under Outdoor Fan After Defrost — Drain Pan Heater Failure

Question

Accepted Answer

Drain pan heater open-circuit or poor connection. Check: Inspect with instruments or visually What to do: Measure drain pan heater resistance — replace if open-circuit (typical: 150–400W, tens to hundreds of Ω) Drain pan heater relay or control signal failure. Check: Inspect with instruments or visually What to do: Check heater power supply: measure AC voltage across heater terminals when defrost mode is active Drain hole blocked. Check: meltwater pools and refreezes What to do: Clean drain hole — remove debris and scale, consider enlarging with drill if needed Refrigerant flow restored too quickly after defrost end, drain pan temperature stays below 0°C. Check: Inspect with instruments or visually What to do: Inspect and replace drain pan heater relay Heater rated capacity insufficient (undersized from initial installation). Check: Inspect with instruments or visually What to do: If drain piping is freezing, add heat tape installation

Ice Buildup Under Outdoor Fan After Defrost — Drain Pan Heater Failure

Likely causes

Drain pan heater open-circuit or poor connection

Drain pan heater relay or control signal failure

Drain hole blocked

Refrigerant flow restored too quickly after defrost end, drain pan temperature stays below 0°C

Heater rated capacity insufficient (undersized from initial installation)

Related cases