Heat6 min
Heat pump defrost
Frost can be normal. A block of ice that never clears is a defrost, airflow, or charge problem.
Normal vs fault
- Light even frost on a cold, damp day is expected. Ice bridging the whole coil with a running fan is not.
- During defrost the outdoor fan should stop, the reversing valve should shift to cool, and the coil should steam.
Checks
- Defrost sensor ohms and placement (OEM clip point, not a random return bend).
- Reversing valve: pressure swap and suction temperature when it should be in defrost.
- Outdoor fan relay on the board — a fan that stays on in defrost will not clear the coil.
- Charge. A starved outdoor coil in heat ices fast and defrosts poorly.
- Aux / emergency heat should stage if defrost is long — confirm W2 / E wiring.