Outdoor coil iced solid — no defrost

Heating / heat pump

AirCompDX - Field Reference for Air Compressor Techs
All HVAC symptoms
1

Defrost board / sensor failure

high
CheckBench test board timing; check defrost thermistor resistance vs curve.
FixReplace defrost sensor first; then board.
2

Reversing valve won't shift

high
Check24 V at solenoid but no shift.
FixReplace solenoid coil; replace valve body if stuck.
Safety

Pull the disconnect and lock out before opening HVAC equipment. Discharge dual-run capacitors before handling. Refrigerant recovery and brazing require EPA 608 certification and proper PPE.