Defrost fault in a heat pump: when defrost does not start or does not complete

If the outdoor unit freezes excessively or the defrost does not complete, the diagnosis must examine both the sensors and the refrigerant circuit.

Possible causes

Faulty coil sensor, four-way valve, insufficient thermal capacity, or controller problem.

What we record

Coil temperature before and after, defrost duration, and whether the direction of the refrigerant cycle actually changes.

Avoiding errors

We do not consider every instance of icing as a malfunction. We judge the outcome of the defrost cycle.