F9
Pioneer Indoor Auxiliary Temperature Sensor Fault (e.g., Pipe or Mid-Coil Sensor)

Indoor unit shows F9 and may not maintain set temperature accurately

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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 auxiliary sensor, Sensor dislodged from piping, Damaged harness, Indoor PCB sensor input failure

How to Fix / Troubleshooting

Safety first: Disconnect power to the indoor unit before accessing internal sensors.

Steps to try:

  • Identify auxiliary sensor: Some Pioneer models use an additional sensor on the refrigerant piping inside the indoor unit. Locate it by tracing small sensor wires from the coil area to the PCB.
  • Check attachment: Ensure the sensor is firmly strapped to the pipe and insulated as originally installed.
  • Inspect wiring: Look for pinched or cut wires and reseat the connector on the PCB.
  • Test operation: Restore power and run the unit. If F9 returns, the sensor is likely defective.

When to call a pro: If replacing the auxiliary sensor does not clear F9, the indoor PCB may need replacement.

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Repair Difficulty

Medium 3/5

Required Part

Indoor Pipe Temperature Sensor (Auxiliary NTC)
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