Freezer displays E4; the unit may not defrost properly or may over-defrost.

Safety first: Disconnect power before testing the heater or thermostat. The defrost heater operates at line voltage.

• Access evaporator and heater: Remove the interior rear panel to expose the evaporator and heater assembly (usually at the bottom or woven through the coil).
• Check heater continuity: Disconnect heater leads and test with a multimeter. A good heater typically shows low resistance (e.g., 20–100 Ω). If open (OL), replace the heater.
• Test defrost thermostat/bi-metal: With the evaporator cold (below freezing), the thermostat should show continuity. If it is open when cold, replace it.
• Inspect wiring and connectors: Look for burnt connectors or melted insulation near the heater. Repair with high-temperature rated connectors.
• Control board check: If the heater and thermostat test good, the defrost relay or triac on the control board may have failed. Inspect for burn marks and replace the board if necessary.