F4
Carrier
Outdoor Coil Temperature Sensor Fault
Indoor unit shows F4 and heating or cooling capacity is unstable
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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 coil thermistor, Sensor not properly attached to coil or tubing, Damaged harness, Outdoor PCB sensor input failure
How to Fix / Troubleshooting
Safety: Disconnect power at the outdoor disconnect.
- Step 1 – Access sensor: Remove the outdoor unit service panel and locate the thermistor clipped to the condenser coil or refrigerant line.
- Step 2 – Verify contact: Ensure the sensor is firmly attached and insulated as originally installed.
- Step 3 – Inspect wiring: Check for corrosion at connectors and damage along the wire path. Reseat the connector on the PCB.
- Step 4 – Replace sensor: If F4 remains, replace the outdoor coil temperature sensor.
- Step 5 – PCB replacement: If the fault persists, the outdoor control board may be defective and should be replaced by a Carrier technician.
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Repair Difficulty
Medium
3/5
Required Part
Outdoor Coil Temperature Sensor
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