Found defrost board not defrosting on test - replaced defrost board and cycled defrost to melt the rest of the outdoor unit and checked defrost thermistor. Found defrost thermistor will also have to be replaced - defrost thermistor was already on order but was not in at time of call - will call as defrost thermistor comes in to schedule return trip - returned 12/12/25 with defrost thermistor - replaced thermistor and cycled system to check operation. Everything runs normally again!