Fan, Cooling: Operation

The two speed cooling fan system uses three relays to control the cooling fan operation. These are the series-parallel fan relay, LO-HI fan relay and HI-MED. fan relay. During low speed mode, the cooling fan and cooling fan resistor operate in series, splitting the 12 volt source between the resistor and the cooling fan motor. During high speed mode, the cooling fan motor and resistor operate in parallel to one another, with each receiving a separate 12 volt source.

Since there are many variables that affect exactly when the cooling fans will operate, including but not limited to: A/C head pressure, A/C status, engine coolant temperature, engine oil temperature, battery temperature, transmission oil temperature, charge air temperature, Engine Thermal Management (ETM), vehicle speed, anti-steaming function and more depending on vehicle configuration and software calibrations, all of which can affect when the cooling fans will operate. An exact temperature when the fans will turn on and off is not practical to predict.

For cooling fan diagnosis and testing. Refer to DIAGNOSIS AND TESTING .