The fan clutch is a component of the cooling system that varies the fan speed to meet the cooling needs of the engine. Nearly all rear wheel drive vehicles use fan clutches to control fan speed because of their ability to provide high volumes of air and good fuel economy. Despite their popularity, they are one of the least understood cooling components. There are three types of fan clutches: non-thermal (also called centrifugal clutches), thermal and electronic. Use of the wrong fan clutch may result in poor cooling, excessive noise, reduced fuel economy or fan clutch failure.