Freezer displays E4 and may not defrost; heavy frost or ice accumulates on evaporator and back wall.

Safety first: Unplug the freezer. Ice and water may be present; keep the work area dry to avoid slipping and electrical hazards.

Steps:

• Access evaporator area: Remove food and shelves, then remove the rear interior panel to expose the evaporator coil.
• Locate defrost sensor: Insignia freezers may use a round defrost thermostat (bi-metal) clipped to the evaporator tubing, or a small thermistor attached near the coil.
• Check continuity (bi-metal): If using a thermostat, with the evaporator still cold (below freezing), test continuity across the thermostat. It should read closed (0Ω). If it is open when cold, replace it.
• Test thermistor type: If a thermistor is used, measure resistance at a known temperature and compare to spec. Replace if open/shorted.
• Inspect wiring: Look for brittle or burned wires near the defrost heater and sensor. Repair or replace damaged sections and ensure connectors are tight.
• Replace faulty parts: Install a new defrost thermostat or defrost thermistor as appropriate, clipping it securely to the evaporator tubing.
• Control board check: If the sensor tests good and wiring is intact but E4 persists, the main control board may not be reading the sensor correctly and may need replacement.

Warning: Do not bypass the defrost thermostat permanently; it is a safety device that prevents overheating.