E4
York
Indoor Coil Temperature Sensor Fault / Freeze Protection
York inverter or digital AC shows E4 and stops cooling or heating
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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
Failed indoor coil thermistor, Thermistor out of position, Iced evaporator coil from low airflow, Control board misreading sensor
How to Fix / Troubleshooting
Safety: Turn off power to the indoor unit at the breaker before removing covers.
- Check air filter and airflow: Replace dirty filters and ensure return and supply vents are not blocked. Run the fan only for 1–2 hours to thaw any ice on the coil.
- Inspect coil sensor placement: Remove the front panel of the York indoor unit. Locate the coil thermistor clipped to the evaporator tubing. Make sure it is firmly attached and not hanging loose.
- Check sensor wiring: Look for broken insulation, loose plugs, or corroded connectors between the thermistor and the indoor PCB. Reseat connectors.
- Test/replace thermistor: Using an ohmmeter, measure resistance at room temperature and compare to York service data. If readings are open, shorted, or far off spec, replace the coil temperature sensor.
- If error persists: The indoor control board may be faulty and should be diagnosed and replaced by a qualified technician.
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Repair Difficulty
Medium
3/5
Required Part
Indoor Coil Temperature Sensor
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