Safety: Unplug the unit and allow it to cool before working near the compressor.

Steps to resolve H3:

Improve ventilation: Ensure the rear of a window unit is fully outside with unobstructed airflow. For portable units, verify the exhaust hose is properly installed and not restricted.
Clean condenser coil: Remove the outer shell and clean the condenser fins thoroughly.
Check condenser fan: Confirm the outdoor fan starts and runs at full speed when cooling is demanded. Replace the condenser fan motor if it fails to run or is noisy and slow.
Electrical check (advanced): A technician should measure compressor current draw and compare to nameplate values. Excessive current may indicate a failing compressor or incorrect refrigerant charge.
Persistent H3: If H3 recurs after cleaning and fan repair, the compressor or main PCB may be defective. Professional diagnosis and possible compressor or main control board replacement are required.

Unit shows H3 and shuts down compressor; fan may continue to run.

Possible Causes