Freezer displays E4 and may stop automatic defrost; heavy ice builds up on the evaporator and rear wall.

Safety: Unplug the freezer before any work. Defrost components can be live and hot during operation.

Steps to check:

• 1. Manually defrost: Turn off and fully defrost the freezer to remove all ice from the evaporator. This will allow access and may temporarily restore function.
• 2. Access evaporator and defrost components: Remove the internal rear panel to expose the evaporator coil, defrost heater (usually a metal or glass tube at the base or woven through the coil), and defrost sensor/thermostat.
• 3. Inspect defrost sensor and thermostat: Look for cracked housings, burnt connectors, or loose mounting. The defrost sensor is often an NTC; the thermostat is a small round or oval device clipped to the coil.
• 4. Test continuity: With the unit unplugged, disconnect the defrost heater and measure resistance. A typical heater will show some resistance (tens to hundreds of ohms). An open circuit indicates a failed heater. Check the defrost thermostat or thermal fuse for continuity when cold; an open device is faulty.
• 5. Replace faulty parts: If the heater is open, replace with an "Amica Defrost Heater" specified for your model. If the thermostat or defrost sensor is open or out of spec, replace with the correct "Defrost Thermostat" or "Defrost NTC Sensor".
• 6. Control board check: If all components test good but E4 persists, the defrost relay or triac on the main PCB may be defective. This typically requires board replacement by a professional.

Note: Never bypass a thermal fuse or thermostat; they are critical safety devices.