Trane air conditioner shows F9 and may not operate correctly in defrost or low ambient conditions (heat pump models).

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.

Possible Causes

Failed defrost sensor, Loose sensor on outdoor coil, Faulty defrost control logic on board, Damaged sensor wiring

Safety first: Turn off power to the outdoor unit before accessing the coil and control board.

Locate defrost sensor: Typically clipped to the outdoor coil tubing. Ensure it is firmly attached and in good contact.
Inspect wiring: Check for damaged or pulled sensor wires, especially where they pass through sheet metal.
Clean coil: A heavily iced or dirty coil can confuse defrost sensing. Clean the coil and allow ice to melt completely.

If F9 persists, the defrost sensor or outdoor control board may need replacement by a Trane technician.

Hard 4/5

Trane Defrost Sensor

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