A fan belt is a relatively long, flat, multi-ribbed belt that is driven by the engine’s crankshaft pulley. The belt drives many, and often all, of the engine accessories such as the alternator, air conditioning compressor, power steering pump, water pump, and air pump. The fan belt is tensioned by a hydraulic or spring-loaded automatic tensioner. Some older cars use a serpentine belt to drive most accessories but will also have a shorter v-style belt to drive, for example, the power steering pump.