Freezer displays E4; unit may not defrost properly or may over-defrost, causing temperature swings.

Safety: Disconnect power before testing the defrost system. The defrost heater operates at line voltage.

• Access evaporator area: Remove interior rear panel to expose the evaporator coil and defrost components.
• Locate defrost heater: The heater is usually a glass-encased or metal-sheathed element mounted at the bottom or woven through the evaporator.
• Check continuity: Disconnect heater leads and test with a multimeter. A good heater typically shows low resistance (10–100 Ω). If open (OL), replace the heater.
• Inspect defrost thermostat/bi-metal: This safety device is clipped to the evaporator tubing. At freezing temperatures, it should show continuity. If it is open when cold, replace it.
• Inspect wiring and connectors: Look for burned or discolored connectors at the heater and thermostat. Repair or replace damaged connectors using high-temperature-rated terminals.
• Board check: If heater and thermostat test good, the main control board may not be energizing the heater. This requires live-voltage diagnostics and is best handled by a technician.

After replacing any failed components, reassemble panels, restore power, and monitor for normal defrost operation and clearing of the E4 code.