Freezer display shows F4; defrost cycles may not run correctly; heavy ice build-up on evaporator.

Safety first: Disconnect mains power. Be cautious of sharp evaporator fins.

Steps:

• Defrost manually: Remove food to a backup freezer or cool box. Leave the door open and allow the unit to defrost fully for 12–24 hours, placing towels to catch water. Do not use heat guns or knives.
• Access evaporator: Remove drawers and the rear interior panel to expose the evaporator and defrost components.
• Locate defrost sensor/thermostat: On Liebherr freezers, this is usually clipped to the evaporator tubing or attached to the coil with a metal clip or plastic holder.
• Check continuity: With the part at room temperature, test the defrost thermostat (if present) for continuity and the NTC sensor for reasonable resistance. An open thermostat or sensor reading out of range indicates failure.

Remedy: Replace the defrost sensor/thermostat assembly with the correct Liebherr part. Route wiring away from sharp edges and reattach firmly to the evaporator. Refit the evaporator cover to ensure proper airflow.