Wine cooler displays E4 and may not defrost properly, leading to ice buildup on the evaporator.

Safety warning: Unplug the wine cooler before accessing the evaporator or control board. Sharp metal edges and live circuits can cause injury.

Steps:

• Inspect for frost buildup: Remove interior panels to view the evaporator. Heavy, solid ice indicates a defrost problem.
• Locate defrost sensor: The defrost thermistor is usually clipped to the evaporator tubing. Check that it is firmly attached and not dangling.
• Test defrost thermistor: With the unit unplugged, disconnect the thermistor and measure resistance. Compare to spec at the measured coil temperature (often lower than room temp). Replace if readings are open, shorted, or far off spec.
• Check defrost heater: Disconnect heater leads and measure continuity with a multimeter. A good heater shows low resistance (a few tens of ohms). If open, replace the defrost heater assembly.
• Inspect wiring and connectors: Look for burnt connectors, melted insulation, or broken wires between heater, sensor, and control board. Repair with proper connectors and heat-shrink.
• Control board: If heater and sensor test good but E4 persists and defrost never initiates, the main control board defrost relay or logic may be faulty and should be replaced by a technician.
• Manual defrost: As a temporary measure, power off the unit, remove food, and allow ice to melt completely. Do not chip ice with sharp tools.