Freezer displays E4 and may stop cooling or enter a protective mode

Safety warning: Unplug the freezer before accessing the evaporator or control board. The defrost heater and wiring can be live and hot during operation.

Diagnostic steps:

• Access evaporator compartment: Remove interior rear panel to expose the evaporator coil, defrost heater, and defrost sensor.
• Inspect for heavy ice buildup: If the evaporator is encased in ice, the defrost system is not working properly. Manually defrost by leaving the unit unplugged with doors open and towels to catch meltwater.
• Check defrost sensor (thermistor): Locate the defrost sensor clipped to the evaporator. Inspect wiring and connector. Test resistance at known temperatures; replace if readings are open/shorted or out of spec.
• Test defrost heater: With the unit unplugged, disconnect heater leads and measure resistance. A typical heater will show a finite resistance (often 20–200 Ω). An open circuit indicates a failed heater that must be replaced.
• Check thermal fuse/defrost thermostat: If present, test continuity at freezing temperatures. Replace if open when it should be closed.
• Control board: If all defrost components test good, the main control board defrost relay or logic may be faulty. Inspect for burnt spots and consider replacement.

Note: Do not chip ice off the evaporator with sharp tools; this can puncture refrigerant lines and permanently damage the freezer.