Dehumidifier displays E4 and stops running, often after a short period

Safety: Unplug the unit. Allow any ice on the coil to melt before working near it to avoid water on electrical parts.

Steps to address E4:

• Check for icing: Remove the front grille and filter. Inspect the evaporator coil. If it is heavily iced, let it thaw completely and ensure room temperature is above 65°F before further testing.
• Access defrost sensor: Remove the front or side panel to fully expose the evaporator. The defrost sensor is usually a thermistor clipped to the coil tubing or fins, sometimes the same sensor as the evaporator sensor, sometimes separate.
• Verify attachment: Make sure the sensor is firmly clipped to the coil and not dangling. A loose sensor can misread temperature and trigger E4.
• Inspect wiring: Look for chafed insulation where the harness passes near metal edges. Repair with electrical tape or replace the harness if conductors are exposed.
• Test/replace sensor: If you have a meter, test the thermistor resistance at room temperature and compare to specifications (or to a known-good sensor). Replace the defrost sensor if readings are open, shorted, or far out of range.
• Control board check: If a new sensor does not clear E4, the defrost control circuit on the main control board may be defective and the board should be replaced.

Note: Persistent icing plus E4 can also indicate low refrigerant or restricted airflow; those require a licensed technician.