Display shows E4 and compressor or fan operation is erratic; unit may shut down unexpectedly.

Disconnect power before working on the unit.

• Check for heavy frost: Open the cooler and inspect the rear interior panel. If it is heavily frosted or iced over, the evaporator sensor may not be reading correctly.
• Defrost the unit: Turn the cooler off, unplug it, and leave the door open for several hours until all ice melts. Place towels to catch water. Do not chip ice with sharp tools.
• Remove rear interior panel: With the unit unplugged, remove screws holding the evaporator cover and gently pull it forward to expose the evaporator coil and sensor.
• Locate the evaporator sensor: It is usually clipped to the evaporator tubing or attached with a metal clip or tape. Ensure it is firmly in contact with the coil.
• Inspect and test: Check the sensor and wiring for damage. If you have a multimeter, test resistance at room temperature and compare to the expected NTC range. A reading of open or short indicates failure.
• Re-seat or replace: If the sensor has slipped out of position, reattach it securely to the coil. If faulty, replace it with a compatible hOmeLabs evaporator temperature/defrost sensor.
• Reassemble: Reinstall the evaporator cover, ensuring no wires are pinched, then restore power and confirm that E4 is cleared.

Warning: If E4 returns quickly and the sensor tests good, the main control board's sensor circuit may be defective and should be evaluated by a technician.