Wine cooler shows E4 and compressor or fan may not run correctly.

Safety: Unplug the unit. The defrost circuit involves line voltage; do not test live unless you are trained and using proper tools.

• Access evaporator area: Remove interior rear panel to expose the evaporator coil and defrost components.
• Locate defrost sensor: It is usually clipped to the evaporator tubing near the defrost heater. Inspect for physical damage or corrosion.
• Test defrost sensor: Disconnect and measure resistance. At frozen temperatures it should read higher resistance than at room temperature. An open or shorted reading indicates failure; replace with a Summit defrost sensor.
• Check defrost heater: With the unit unplugged, disconnect heater leads and measure resistance. A typical heater will show a finite resistance (often 50–300Ω). An open circuit means the heater is bad and must be replaced.
• Inspect wiring and connectors: Look for burnt connectors or melted insulation around the heater and sensor wiring.
• Control board check: If sensor and heater test good, the main control board defrost relay or triac may be faulty. Replace the board if there are signs of damage or if E4 persists.