Safety: Unplug the unit. Do not attempt to open sealed refrigeration components.

Steps:

Allow thawing: If the unit was operating in a very cold room, move it to a warmer area (above 65°F / 18°C), unplug it, and let it sit for 4–6 hours to fully defrost. Then retry.
Access coil sensor: Remove the front or rear cover to expose the evaporator coil. Locate the defrost sensor clipped to the coil tubing.
Check attachment: Ensure the sensor is firmly clipped to the coil and not loose. Reattach securely.
Inspect wiring: Look for damaged insulation or loose connectors between the sensor and control board.
Test sensor: Measure resistance at room temperature and compare to Honeywell’s spec. Replace the sensor if readings are out of range.
Refrigeration issues: If the sensor is good but the coil ices up rapidly or E4 persists, the sealed system may be undercharged or restricted. This requires a licensed refrigeration technician.

Warning: Do not puncture or cut any copper tubing; refrigerant release is hazardous and illegal to vent.

Dehumidifier shows E4 and stops; unit may beep and refuse to start a cycle.

Possible Causes