Freezer displays F4 and may not defrost properly, leading to ice buildup on the evaporator

Safety first: Unplug the freezer. The defrost heater and wiring can be sharp and may have exposed metal edges nearby.

• Access evaporator and heater: Remove the inner rear panel of the freezer to expose the evaporator coil and defrost heater assembly.
• Visual check: Look for burnt spots on the heater, broken heater elements, or disconnected wires.
• Test heater resistance: Disconnect the heater leads and measure resistance with a multimeter. A typical heater will show a finite resistance (e.g., 50–300 Ω). An open circuit indicates a failed heater.
• Check defrost thermostat/fuse: Locate the defrost bimetal thermostat or thermal fuse clipped to the evaporator. Test for continuity at freezing temperature. Replace if open.
• Inspect wiring and connectors: Ensure all connectors from the heater and thermostat to the main control PCB are tight and not corroded.
• Replace faulty parts: Install a new Hitachi defrost heater and/or defrost thermostat/thermal fuse as needed. Reassemble panels carefully to avoid air leaks.
• Control PCB: If the heater circuit tests good but F4 persists and defrost never initiates, the main control PCB defrost relay may be defective and the board should be replaced.