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

Safety warning: Disconnect power before accessing the evaporator or rear service panel. The defrost heater and wiring can be live when energized.

Diagnostic steps:

• Inspect frost pattern: Remove the interior rear panel and check the evaporator. Heavy, solid ice buildup indicates a defrost problem.
• Check defrost sensor: Locate the defrost sensor clipped to the evaporator. Test its resistance at known temperature and compare to spec. Replace if open, shorted, or out of range.
• Test defrost heater: With power off, disconnect heater leads and measure resistance. A typical heater will show finite resistance (often 50–200 Ω). An open circuit indicates a failed heater that must be replaced.
• Inspect wiring and connectors: Look for burnt connectors, melted insulation, or corroded terminals in the defrost circuit.
• Control board: If sensor and heater test good, the main control board’s defrost relay or logic may be faulty. Replace the board if no other issues are found.

After repair: Manually defrost any remaining ice with towels and ambient air (do not use sharp tools or high heat), reassemble, and restore power. Monitor for normal frost pattern and absence of E4.