Freezer shows E4 and may defrost too often or not defrost at all, leading to heavy ice build-up.

Safety warning: Unplug the freezer. The defrost heater area can have sharp metal edges and may still be hot if recently in defrost mode.

Procedure:

• 1. Defrost manually: If the evaporator is heavily iced, allow the freezer to defrost fully (doors open, towels in place). Do not use sharp tools to chip ice.
• 2. Access evaporator assembly: Remove the internal rear panel to expose the evaporator, defrost heater, and defrost sensor/thermostat.
• 3. Identify components: The defrost NTC is usually clipped to the evaporator tubing; the defrost thermostat (if fitted) is a small round or oval device clamped to the coil.
• 4. Test the defrost thermostat: At room temperature it may be open; when cold (below its cut-in temperature) it should show continuity. If it never closes or is physically damaged, replace it.
• 5. Test the defrost NTC: Measure resistance and compare to expected values. Replace if open, shorted, or out of range.
• 6. Wiring and PCB: Inspect the harness for brittleness or burn marks. If sensors and thermostat are good, the main control PCB defrost circuit may be defective and require replacement.

Note: Always refit sensors and thermostats in the original positions to ensure correct temperature sensing.