F1
Fraser-Johnston
Indoor Ambient Temperature Sensor Fault
F1 displayed, indoor unit stops or runs erratically
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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 room temperature thermistor, Loose sensor connection on indoor PCB, Sensor out of calibration, Damaged sensor wiring harness
How to Fix / Troubleshooting
Safety: Turn off power to the indoor unit before removing the front cover.
- Locate sensor: On Fraser‑Johnston wall-mount or console units, the room sensor is usually near the air intake grille, connected by small-gauge wires to the main PCB.
- Check connection: Ensure the thermistor plug is fully seated on the control board and that wires are not pinched or broken.
- Test resistance: Disconnect the sensor and measure its resistance with a multimeter. Compare to the Fraser‑Johnston thermistor chart (e.g., around 10kΩ at 77°F, depending on model). If reading is open, shorted, or far off spec, replace the sensor.
- Replace sensor: Install a new indoor ambient thermistor with the correct part number. Route wires away from high-voltage components.
- Power up and test: Restore power and verify that F1 clears and temperature control is stable.
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Repair Difficulty
Medium
3/5
Required Part
Indoor Ambient Thermistor
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