Safety: Disconnect power before opening the cabinet. Water from melted frost can drip; protect floors.

Steps:

Thaw the unit: Turn the unit off and unplug it. Open any access panels and allow all ice on the evaporator coil to melt completely (this can take several hours). Do not chip ice with sharp tools.
Check air filters and vents: Clean the intake filter and ensure that supply and exhaust vents are not blocked. Poor airflow is a common cause of excessive frost.
Locate defrost/frost sensor: This sensor is usually clipped to the evaporator coil. Confirm it is firmly attached and not hanging loose.
Inspect wiring: Look for damaged insulation or loose connectors between the sensor and the main control PCB.
Test sensor: Measure resistance at room temperature and compare to other NTC sensors in the unit. Replace if open/shorted or if readings are clearly out of range.
Reassemble and test: After replacing the defrost/evaporator sensor or correcting airflow issues, reassemble the unit, restore power, and test in cooling mode.
Control board: If E4 returns with a known-good sensor and proper airflow, the main control PCB may be defective and require replacement.

Unit shuts down and displays E4; may occur during defrost or in low ambient conditions.

Possible Causes