The A/C condenser fan blade is a set of plastic blades attached to the condenser fan motor. The fan rotates to pull or push ambient air through the condenser fins, aiding in heat transfer. This airflow is critical when the vehicle is stopped or moving slowly, as there is not enough natural headwind to cool the refrigerant.
Fan blades are usually made of plastic and can get brittle and crack over time. If a stone hits the fan, it can chip or break a blade. This throws the fan assembly out of balance, causing severe vibrations and humming noises when the A/C is turned on.