F2
Armstrong Air
Indoor Temperature Sensor / Thermistor Fault
Indoor unit flashes F2, cooling may be locked out, thermostat may show indoor temperature error
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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 indoor air temperature sensor, Open or shorted sensor wiring, Sensor not properly located in return air stream, Faulty indoor control board sensor circuit
How to Fix / Troubleshooting
Safety first: Turn off power to the indoor unit before accessing the control compartment.
Steps:
- 1. Identify sensor type: On some Armstrong Air systems, the indoor sensor is built into the thermostat; on others, it is a separate thermistor connected to the indoor board. Consult the wiring diagram.
- 2. Inspect sensor placement: If separate, ensure the sensor is mounted in the return air stream and not touching hot components.
- 3. Check wiring: Look for loose or damaged wires between the sensor and the board. Reseat connectors.
- 4. Measure resistance: With power off, disconnect the sensor and measure resistance. Compare to the manufacturer’s temperature/resistance chart. Replace if readings are out of range.
- 5. Reset system: Restore power and clear the fault by cycling power. If F2 returns with a known-good sensor, the indoor board may be defective.
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Repair Difficulty
Medium
3/5
Required Part
Indoor Air Temperature Sensor
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