Wine cooler beeps and displays E4; compressor or fans may not start.

Safety warning: Disconnect power before accessing the evaporator or control board. Avoid contact with sharp fins on the evaporator.

Steps to address E4:

• Visual inspection: Remove interior shelves and the rear liner panel to expose the evaporator and defrost components. Look for heavy ice buildup, burnt wiring, or disconnected plugs.
• Check the defrost sensor: The defrost thermistor is usually clipped to the evaporator coil. Ensure it is firmly attached and not physically damaged.
• Test the defrost thermistor: With a multimeter, measure resistance at room temperature. If it reads open or shorted, replace it with a Whynter-compatible defrost sensor.
• Inspect the defrost heater (if equipped): Look for a heater element at the base or around the evaporator. Check continuity with a multimeter; if open, the heater must be replaced.
• Check wiring and connectors: Follow the defrost circuit wiring back to the control board. Reseat connectors and look for signs of overheating or corrosion.
• Manual defrost: If there is heavy ice, allow the unit to defrost fully by unplugging it and leaving the door open for several hours. Protect the floor from water. After defrosting, restore power and see if E4 returns.

If E4 persists after sensor/heater checks, the control board's defrost relay or logic may be faulty and should be evaluated or replaced by a professional.