Genuine Daikin 4006027 Outdoor Fan Propeller is the large 681 mm propeller that sweeps air through the outdoor condenser coil, doing the physical work of moving heat away from the unit. A cracked, chipped, or unbalanced propeller usually makes itself heard — a new vibration, a knocking note, or a drop in the volume of air leaving the unit. Because the genuine propeller is moulded and balanced to Daikin's exact size and pitch, it runs smooth and quiet where a mismatched blade can shake the whole fan assembly.