Indoor unit displays F3; compressor may not start or may shut down quickly; often associated with discharge temperature issues.

Safety: Power off at the breaker. The discharge line can be extremely hot during operation; only work when the unit has been off long enough to cool.

Steps:

• 1. Access compressor area: Remove the outdoor unit service panel to expose the compressor and discharge line.
• 2. Locate discharge sensor: Find the sensor clipped or strapped to the small-diameter copper pipe leaving the compressor (discharge line).
• 3. Check attachment: Ensure the sensor is firmly in contact with the pipe and secured with a clip or strap. Re-secure if loose.
• 4. Inspect wiring: Follow the sensor wires to the PCB. Look for heat damage, melted insulation, or loose connectors.
• 5. Measure resistance: With power OFF, disconnect the sensor and measure resistance. Compare with other NTC sensors or manufacturer data. Replace if open/shorted.
• 6. Replace sensor: Install a new Airwell discharge temperature sensor. Secure it tightly to the discharge line and insulate if originally insulated.
• 7. PCB check: If sensor and wiring are good, the outdoor PCB may be defective and require replacement by a technician.