Description & Operation
An electric fan is mounted on the fan cowl and acts by drawing air through the radiator. Under certain operating conditions, the engine control activates the electric fan at various speeds. The electric fan is activated by means of a power output stage directly on the fan motor. The motor control module activates this power output stage by means of a square-wave signal with duty factors (variable pulse width) between 10 and 90 percent, thus controlling the various speeds of the electric fan. Pulse duty factors less than 5 percent and greater than 95 percent do not trigger activation but rather they are used for fault detection purposes. The power output stage features its own positive and ground supply. The fan speed is influenced by the coolant temperature at the radiator outlet and the pressure in the air conditioning system. The fan speed is reduced as the vehicle speed increases. See WIRING DIAGRAMS . See Fig 1 .