Display shows E4 and the compressor or cooling system does not operate correctly (may not start or may run continuously).

Safety first: Unplug the unit. If you see heavy ice buildup, do not chip it with sharp tools; allow it to melt.

Steps to address E4:

• 1. Inspect for frost buildup: Remove interior shelves and the rear evaporator cover. Look for heavy ice accumulation on the evaporator coil. Excessive frost suggests a defrost issue.
• 2. Locate defrost sensor: The defrost NTC is usually clipped to the evaporator tubing or attached to the coil with a metal clip or tape. Inspect for damage or dislodging.
• 3. Check wiring: Follow the sensor and heater wires to the main harness. Look for brittle insulation, burn marks, or loose connectors.
• 4. Test the defrost sensor: With the unit unplugged, disconnect the sensor and measure resistance. Compare to the expected NTC curve. Replace if open/shorted.
• 5. Manually defrost: If there is heavy ice, leave the door open and allow the unit to defrost completely for 12–24 hours with towels to catch water. Do not use heat guns near plastic parts.
• 6. Replace faulty parts: If the sensor is bad, install a new "STAIGIS defrost/evaporator sensor". If the heater is open (infinite resistance), replace the "evaporator defrost heater" if your model uses one.

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