I have a trane heat pump the out side unit is getting thick ice on coils how to fix problem
I have model #s for out side unit and for under house unit if it helps.

The problem is usually in the defrost circuit. The fix is to check and replace the defective part in the defrost circuit. Usually a circuit board or a sensor.

If its heating just fine once the OD unit is defrosted, then it is likely something in your defrost subsystem. If its not producing heat you could be low on refrigerant.

Either way, I would not use the system until you figure this out. You could cause damage freezing the outdoor unit.