Display shows E4 and the unit may stop cooling or run erratically; defrost cycles may not occur correctly.

Safety warning: Disconnect power before accessing the evaporator or control board. The defrost heater and surrounding metal can be sharp and may retain heat.

Diagnostic procedure:

• 1. Access evaporator area: Remove interior shelves and the rear liner panel to expose the evaporator coil and defrost components.
• 2. Locate defrost sensor: The defrost NTC is typically clipped to the evaporator tubing or attached near the defrost heater. Inspect for physical damage or dislodging.
• 3. Check for heavy ice buildup: Excessive frost on the evaporator indicates a defrost failure. Manually defrost by leaving the unit unplugged with doors open and towels in place until all ice melts.
• 4. Test defrost sensor: With the unit at room temperature, disconnect the sensor and measure resistance. Compare to the manufacturer’s NTC chart. Replace if readings are out of range.
• 5. Test defrost heater: Disconnect heater leads and measure resistance. An open circuit indicates a failed heater. Visually inspect for burn marks or breaks.
• 6. Inspect wiring and control board: Check harnesses from sensor and heater to the main control board. Look for burnt connectors or signs of overheating at the defrost relay on the board.
• 7. Replace faulty components: Install a new defrost sensor or heater as needed, ensuring proper mounting and insulation. If the relay or board is defective, replace the main control module.
• 8. Reassemble and test: Reinstall panels, restore power, and monitor for normal cooling and absence of E4 over several hours.

Professional assistance: If you are not experienced with electrical testing or if the control board is suspected, contact an authorized Gaggenau service provider.