Freezer displays E4 and may not defrost; ice buildup on evaporator and poor cooling.

Safety first: Unplug the freezer before testing the heater. The defrost heater operates at mains voltage and can cause shock.

• 1. Access the evaporator and heater: Remove interior shelves and the rear panel to expose the evaporator. The defrost heater is typically a metal or glass-encased element at the bottom or woven through the coil.
• 2. Visual inspection: Look for burn marks, broken heater tubes, or melted wiring insulation.
• 3. Test heater resistance: Disconnect the heater leads and measure resistance with a multimeter. Typical values are 20–150 Ω depending on model. An open circuit (OL) indicates a failed heater that must be replaced.
• 4. Check wiring and connectors: Inspect the harness from the heater to the control board. Repair any burnt or loose connectors and secure them firmly.
• 5. Test for power during defrost (advanced): With the unit reassembled and powered, and using extreme caution, place the unit into a forced defrost mode (per service manual) and measure voltage at the heater. If no voltage is present but the board should be energizing it, the defrost relay or board is faulty.
• 6. Replace the main control board if heater and wiring are good: If the heater tests good and wiring is intact, replace the main control board which contains the defrost relay.