Heating
Heat Pump Defrost Troubleshooting Cheat Sheet
A field-side reference for when the outdoor unit is icing, short-defrosting, or never defrosting at all.
What should happen
- The board should see the right outdoor conditions, initiate defrost, shift the reversing valve, and usually stop the outdoor fan.
- Indoor supplemental heat should keep the discharge air from turning unpleasant during the cycle.
- The board should terminate defrost on temperature or time instead of baking the system too long.
Symptom map
| Symptom | Likely direction | First proof point |
|---|---|---|
| Outdoor coil ices solid, no defrost | Sensor, board, or no call logic | Sensor reading and board inputs |
| Defrost starts but never clears | Reversing valve, charge, or fan issue | Valve shift and coil temperature response |
| Frequent nuisance defrost | Sensor drift or control issue | Sensor resistance and board timing |
Keep yourself honest
- Do not skip outdoor coil cleanliness and fan operation just because the complaint sounds electronic.
- Verify strip heat staging if occupants complain about cold air during defrost.
- If the reversing valve is noisy or inconsistent, prove the coil and control signal before you sell the valve body.