Display shows E4 and the unit may not defrost properly; heavy ice buildup on the evaporator or frequent temperature swings.

Safety warning: Disconnect power before working near the evaporator or electrical components. Water from defrosting ice can create shock hazards.

Steps to diagnose:

• Inspect for frost: Remove interior shelves and the rear inner panel. If the evaporator is encased in ice, the defrost system is not working correctly.
• Locate defrost sensor: On BODEGA43 models with active defrost, a dedicated NTC or combined evaporator/defrost sensor is clipped to the evaporator tubing.
• Check sensor resistance: With the unit unplugged and sensor disconnected, measure resistance. Compare to typical NTC values; replace if open or shorted.
• Check defrost heater (if present): Some compressor-based BODEGA43 wine coolers use a small defrost heater. Measure continuity across the heater terminals; an open circuit indicates a failed heater.
• Inspect wiring and connectors: Look for corrosion or burnt connectors around the evaporator and at the main control board defrost output.
• Manual defrost: Fully defrost the evaporator using towels and a container to catch water. Do not chip ice with tools.
• Replace faulty parts: Install a new defrost sensor (NTC) and/or defrost heater as required. Ensure all connectors are tight and protected from moisture.

When to seek service: If the sensor and heater test good, the main control board defrost circuit or relay may be defective and should be evaluated by a technician.