F4 error displayed; compressor may not start or may shut down quickly; unit not cooling.

Safety first: Unplug the appliance. The compressor area contains live mains voltage when powered. Do not touch refrigerant lines with tools that could puncture them.

Steps:

• 1. Access compressor compartment: Remove the rear lower cover to expose the compressor and control box.
• 2. Inspect wiring: Check that all wires to the compressor and start device are firmly connected and not burnt or discolored.
• 3. Check the start relay/PTC: Remove the plastic cover on the compressor terminals. Gently pull off the start device. Shake it lightly; if it rattles or shows burn marks, it is likely faulty.
• 4. Replace start device (if separate from PCB): Install a new Liebherr-specified start relay/PTC on the compressor, ensuring correct orientation and tight fit.
• 5. Examine the main PCB: If accessible, look for burnt relay contacts or tracks. Do not attempt board-level repair unless qualified.
• 6. Reassemble and test: Refit covers, restore power, and listen for the compressor starting smoothly. Monitor for cooling and verify that F4 does not reappear.

Important: If the compressor hums and trips repeatedly even with a new start device, the compressor itself may be mechanically locked and requires professional replacement.