Display shows E4; unit may stop cooling and fan may run intermittently.

Safety first: Disconnect mains power. The defrost circuit operates at full mains voltage; do not test live unless you are qualified.

Steps to address E4:

• Visually inspect for ice buildup: Remove internal rear panel and check if the evaporator is completely encased in ice. Heavy ice suggests a defrost failure.
• Check defrost sensor: Locate the defrost NTC (often clipped to the evaporator near the heater). Inspect for damage and test resistance with a multimeter. Replace if open/shorted.
• Test defrost heater (if accessible): With the unit unplugged, disconnect heater leads and measure resistance. A typical heater will show a finite resistance (tens to hundreds of ohms). OL indicates an open heater that must be replaced.
• Inspect wiring and connectors: Follow the heater and sensor wires back to the main PCB. Look for burnt connectors, melted insulation, or loose plugs.
• Manual defrost: Fully defrost the evaporator with the unit off and door open. After reassembly, power on and monitor if E4 returns.

If the sensor and heater test good but E4 persists, the defrost relay or control logic on the main PCB is likely faulty and the board should be replaced by a professional.