Wine cooler displays E4 and compressor does not start or cycles rapidly

Safety warning: Unplug the wine cooler before accessing the evaporator or control board. Avoid contact with sharp metal edges.

• Access evaporator area: Remove interior shelves and the rear inner panel to expose the evaporator coil and defrost components.
• Locate defrost sensor and heater: The defrost thermistor is usually clipped to the evaporator tubing; the defrost heater is a tube or wire element at the bottom or around the coil.
• Check for heavy ice buildup: If the evaporator is encased in ice, allow a full manual defrost (unit unplugged, door open) until all ice melts. Do not chip ice with sharp tools.
• Test defrost thermistor: Disconnect the defrost sensor and measure resistance at a known temperature (e.g., ice water). Compare to spec; replace if open, shorted, or out of range.
• Test defrost heater: With the heater disconnected, check continuity with a multimeter. An open circuit indicates a failed heater that must be replaced.
• Inspect thermal fuse/thermostat (if equipped): Check continuity through the defrost safety thermostat or fuse. Replace if open.
• Reassemble and test: After replacing any failed components, reassemble the inner panel, restore power, and monitor operation. If E4 persists and all defrost components test good, the main control board defrost circuit is likely faulty and should be replaced by a technician.