Radiator Cooling Fan: Description and Operation
RADIATOR FANDESCRIPTION
The radiator cooling fan are variable speed electric motor driven fans. The radiator fan assembly includes electric motors, fan blades, and a support shroud that is attached to the radiator. The radiator fan is serviced as an assembly (fan motor/fan/shroud).
OPERATION
The variable speed radiator fans are controlled by the Powertrain Control Module (PCM) by way of three relays located in the Power Distribution Center (PDC). This fan control system provides infinitely variable fan speeds, allowing for improved fan noise, A/C performance, better engine cooling, and additional vehicle power.
To control radiator fan operation, the PCM looks at inputs from:
^ Engine coolant temperature
^ A/C pressure transducer
^ Ambient temperature
^ Vehicle speed
^ Transmission oil temperature (automatic transmission only)
The PCM uses these inputs to determine when the fans should operate and at what speed.
The low speed radiator fan relay drives both fans at approximately six volts through a series circuit and the high speed radiator fan drives both fans at approximately twelve volts through a parallel circuit.
The low speed is active when the high speed id active.
Battery positive voltage is supplied to all three fan relays. When the low speed, fan on, criteria has been met, the NGC grounds the low speed radiator fan relay control circuit. Battery voltage is then passed through the low speed radiator fan relay, through fan number one, through the radiator fan relay, through the second fan to chassis ground. When the high speed, fan on, criteria has been met, the NGC grounds the high speed radiator fan relay control circuit. This shared control also grounds the radiator fan relay control circuit. Battery voltage is then passed through the high speed radiator fan relay to fan number one to chassis ground, and at the same time the radiator fan relay switches to ground and the number two fan operates at the higher voltage.