F3
Fraser-Johnston
Outdoor Ambient Temperature Sensor Fault
F3 displayed, outdoor unit may not run correctly
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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
Open or shorted outdoor ambient thermistor, Sensor exposed to direct sunlight or heat source, Damaged sensor wiring, Faulty outdoor control board
How to Fix / Troubleshooting
Safety: Turn off power at the outdoor disconnect before opening the condenser panel.
- Locate sensor: The outdoor ambient sensor is typically mounted near the condenser coil or on the control panel, exposed to outdoor air.
- Inspect placement: Ensure the sensor is not touching hot discharge lines or in direct sunlight. Relocate slightly if necessary to measure true ambient air.
- Check wiring and connector: Reseat the thermistor connector on the outdoor PCB and inspect for corrosion or damage.
- Test resistance: Measure sensor resistance and compare to the Fraser‑Johnston chart. Replace if readings are abnormal.
- Replace sensor or board: If a new sensor does not clear F3, the outdoor control board sensor circuit may be defective.
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Repair Difficulty
Medium
3/5
Required Part
Outdoor Ambient Thermistor
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