F1
Keystone Indoor Ambient Temperature Sensor Calibration / Fault

Keystone air conditioner displays F1 and may not respond correctly to temperature settings.

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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

Out-of-range room thermistor, sensor not positioned in airflow, wiring harness damage, control board miscalibration

How to Fix / Troubleshooting

Safety: Unplug the unit before accessing internal components.

Steps:

  • Verify actual room temperature: Use a separate thermometer to compare with the AC display. Large discrepancies suggest sensor or board issues.
  • Inspect room sensor: Access the front intake area and locate the ambient sensor. Ensure it is not touching the cold coil directly and is positioned in the return air stream.
  • Check wiring: Look for loose or damaged wires between the sensor and main PCB. Reseat the connector.
  • Measure resistance: Test the sensor with a multimeter and compare to expected NTC values at room temperature. Replace if out of spec.
  • Board replacement: If a new sensor does not resolve F1 and wiring is good, replace the main control board.
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Repair Difficulty

Medium 3/5

Required Part

Room Temperature Sensor (NTC Thermistor)
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