Goodman
Defrost sensor / stuck in defrost
LockoutDefrost path
Outdoor coil sensor open/short/out of range, or the board will not leave defrost (fan off, RV shifted to cool, long steam).
Walk Defrost sensor / stuck in defrost in Diagnose
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First check
1 Is it actually in defrost?
On Goodman GSZC18 confirm the board thinks it is in defrost: OD fan off, RV shifted, indoor calling heat/aux. A failed OD fan in heat ices the coil and looks like a defrost board. Ohms the outdoor coil / defrost sensor vs the board chart. Unplugged sensor is a stuck-defrost classic.
Expect: Defrost only with a cold outdoor coil, not on every call.
The rest of the walkthrough is Diagnose.
On the plates
- Ohms the outdoor coil / defrost sensor vs the board chart. Unplugged sensor is a stuck-defrost classic.
- Board initiating defrost on time with a warm coil? Bad sensor or bad board — prove the sensor first.
- Outdoor fan must restart when defrost terminates. A dead fan motor ices the coil again on the next heat call.