"Waterproof Cooling Fan" AC fan speed is determined by many factors, the two most important reasons is the exchange of fan bearings: ball bearings air bearing long-term gas plasma oxidation, dirt, dust accumulation, will lead to bearing dawdle increased resistance, resulting in "Waterproof Cooling Fan" fan speed gradually decreased. AC fan of oil-bearing, mainly by mutual friction between the stator and the coil rotates, the oil bearing, with the use of a fan, stop work and time consuming, and gradually reduced, caused by the use of "Waterproof Cooling Fan" Fan when working, the wind speed more slowly.