E4 error code and the compressor does not start or cycles off quickly; cooling performance is poor.

Critical safety: Unplug the unit before touching any components near the compressor. Do not attempt sealed-system repairs (refrigerant) unless you are certified.

• Check ventilation: Ensure the cooler has adequate clearance at the back and sides as specified by Aobosi. Overheating due to poor ventilation can trigger E4.
• Inspect the compressor area: Remove the rear lower panel. Look for the black compressor can and the small start device (relay/PTC) attached to its side under a plastic cover.
• Check for obvious damage: Smell for burnt odor, look for melted plastic on the start relay or discoloration on the compressor terminals.
• Test the start relay/PTC: Remove the start device from the compressor. Shake it gently; if it rattles excessively or shows burn marks, it is likely faulty. With a multimeter, check for continuity according to the part’s specifications.
• Replace start device: Install a new OEM Aobosi-compatible compressor start relay/PTC and overload protector. Ensure it is firmly seated on the compressor terminals and the cover is reinstalled.
• Power and monitor: Restore power and listen for the compressor to start smoothly. If the E4 code returns and the compressor hums then clicks off, the compressor itself may be failing and requires professional diagnosis.
• Do not bypass safety devices: Never bypass the overload or relay; this can cause fire or compressor damage.