H21
Panasonic Indoor Heat Exchanger (Coil) Temperature Sensor Fault

Unit stops and displays H21; often associated with abnormal indoor coil temperature readings.

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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 indoor coil thermistor, Loose thermistor clip on evaporator coil, Damaged thermistor harness, Faulty indoor PCB sensor circuit

How to Fix / Troubleshooting

Safety first: Disconnect power before removing covers.

Steps:

  • 1. Access evaporator coil: Remove front panel, filters, and sometimes additional covers to expose the aluminum coil.
  • 2. Locate coil thermistor: It is usually clipped to the coil fins or inserted into a small pocket on the coil.
  • 3. Check attachment: Ensure the sensor is firmly attached to the coil and not hanging loose. Re-clip if necessary.
  • 4. Inspect wiring: Follow the sensor wires back to the PCB, checking for cuts or loose connectors. Reseat the connector.
  • 5. Replace if faulty: If the sensor is physically damaged or tests open/short with a multimeter, replace it with a Panasonic indoor coil thermistor.

If H21 remains after sensor replacement, the indoor PCB may need replacement by a technician.

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Repair Difficulty

Medium 3/5

Required Part

Indoor Coil Thermistor
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