F3
Day & Night
Defrost Sensor / Defrost Control Fault (Heat Pump)
F3 code, unit may not defrost properly in heat pump mode, frost buildup on outdoor coil
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed outdoor coil defrost sensor, Loose sensor clip on coil, Faulty defrost control logic on outdoor PCB, Wiring damage between sensor and board
How to Fix / Troubleshooting
Safety first: Turn OFF power at the outdoor disconnect before accessing the defrost sensor or board.
- Step 1 – Inspect outdoor coil for frost: If the coil is heavily frosted in heating mode and F3 is present, defrost control is suspect.
- Step 2 – Locate defrost sensor: Find the thermistor clipped to the outdoor coil used for defrost. Ensure it is firmly attached and not dangling.
- Step 3 – Check wiring and connector: Follow the sensor wires to the outdoor PCB. Reseat the connector and inspect for damage.
- Step 4 – Sensor test: With power OFF, measure sensor resistance and compare to Day & Night temperature/resistance chart. Replace if out of spec.
- Step 5 – Board evaluation: If sensor is good and F3 persists, the defrost control on the outdoor board may be faulty and should be replaced by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Defrost Sensor (Outdoor Coil Thermistor)
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