Radiator Cooling Fan: Description and Operation

Electric Fan

1908 Infinite Fan Control

An infinite fan control for the radiators has been introduced to sports cars with the 3.6-liter and 3.8-liter engines of the 911 Carrera and 911 Carrera S. This new feature permits infinite control of the fan speed depending on the coolant temperature and the system pressure in the air conditioning system instead of a two-stage control. The air volume required is calculated by the Motronic control module which transmits the information to the gateway control module via the CAN. Gateway then sends the signal to the front control module. The front control module activates the radiator fan control module using a pulse-width modulated (PWM) activation signal which activates the left and right radiator fans correspondingly via the power output.

This has the advantage of requiring less current and therefore creates less of a load on the vehicle electrical system. With staged control, when a temperature threshold was exceeded the next fan speed had to cover the entire allocated temperature range. With infinite control, the fan speed can be continuously adjusted to the actual requirement. This means that the fan speeds can often be reduced, thereby decreasing noise and vibrations.