PC fans are designed to spin for a long time with very little friction and no maintenance. Their internal components are designed with this in mind. Spinning th

PC fans are designed to spin for a long time with very little friction and no maintenance. Their internal components are designed with this in mind. Spinning them rapidly with compressed air introduces all kinds of forces they were never designed for. Depending on the quality of the fan, I've seen them fail immediately, or shortly after having been blown like a turbine. Others seem unaffected and run fine for years. It's best to err on the side of safety. A dead CPU heatsink fan can mean dead CPU in short order.