Wine cooler displays E4 and may not defrost properly; frost or ice accumulates on the evaporator and rear wall.

Safety warning: Unplug the unit before accessing the evaporator or control board. Do not work near energized heater circuits.

Steps to diagnose:

• 1. Inspect for heavy frost: Remove interior shelves and rear panel to view the evaporator. If it is heavily iced over, the defrost system is likely at fault.
• 2. Manually defrost: With power disconnected, allow the unit to thaw completely. Use towels to catch water. Do not use sharp tools or high heat sources.
• 3. Locate defrost thermistor: It is usually clipped to the evaporator tubing. Check that it is firmly attached and not damaged.
• 4. Test defrost thermistor: Disconnect and measure resistance at known temperatures (e.g., in ice water and at room temperature). Replace if readings are out of expected NTC range.
• 5. Test defrost heater: With the unit unplugged, disconnect heater leads and measure resistance. A typical heater will show finite resistance (often 50–300 Ω). An open circuit indicates a failed heater.
• 6. Check wiring and relay: Inspect harness from heater and defrost sensor to the main PCB. Look for burnt connectors or broken wires. If heater and sensor are good, the defrost relay or triac on the board may be defective, requiring PCB replacement.
• 7. Reassemble and monitor: After replacing faulty parts, reassemble panels, restore power, and monitor for several days to ensure frost does not reaccumulate and E4 does not return.

Call a technician: If you are not comfortable testing live heater circuits or accessing the control board, seek professional service.