Ball bearing life is a factor of the fatigue on the bearing generated from the rotation of the balls in the raceway, and also the condition of the grease during operation. Bearing fatigue is mainly caused by the load on the bearing from the fan, and the grease is affected mainly by temperature. However, since Sanyo Denki fans are not considered large for the industry, the fan impellers impart negligible load on the bearings to affect fan life. Therefore, the main component affecting fan life is the bearing grease.