Wine cooler displays E4 and may shut down cooling or run erratically.

Safety warning: Unplug the unit before accessing the evaporator or defrost components. Surfaces may be sharp and may have ice buildup.

Steps:

• Check for heavy frost: Remove interior rear panel (if accessible). If the evaporator is encased in ice, a defrost issue is likely.
• Inspect defrost sensor: Look for a small sensor clipped to the evaporator coil. Check for broken wires or corrosion at the connector.
• Test defrost sensor: Disconnect and measure resistance at freezer-like temperatures (you can place the sensor in ice water). Compare to spec; replace if open/shorted.
• Check defrost heater and fuse: With power disconnected, test continuity of the defrost heater and any inline thermal fuse. Replace if open.
• Manual defrost: If you cannot test components, you can temporarily defrost by unplugging the unit and leaving the door open for 24 hours with towels to catch water. This may clear E4 temporarily but does not fix the root cause.
• Control board: If all defrost components test good, the main control board defrost circuit may be defective and require replacement.