Cooling Fan - Operation

OPERATION

The hydraulic radiator cooling fan used on the 5.7L and 3.0L engines replaces both the electric fan and the engine driven mechanical fan. This provides 5.7L and 3.0L equipped vehicles with heavy trailer towing capability while at the same time reducing unnecessary power drain on both the engine and the vehicles electrical system.

HYDRAULIC FAN STRATEGY

The hydraulic radiator cooling fan is controlled by the FCM. A PWM (Pulse With Modulated) signal from the JTEC controls the fan speed. There are four inputs to the FCM that determine what speed percentage of fan is required by the vehicle. These inputs are:

- Engine Coolant Temperature
- Transmission Oil Temperature
- A/C System Pressure

By monitoring these three parameters, the FCM can determine if cooling airflow is required. If airflow is required, the FCM will slowly ramp up (speed up) the fan speed until the parameter(s) are under control. Once the temperature or pressure is reduced to within operating parameters the fan will ramp up, ramp down, or hold its speed to maintain the temperature / pressure requirements.

NOTE: Even if the FCM is not requesting fan on operation the fan blade will usually spin between 100 and 500 RPM when the vehicle is at idle. This is due to a controlled minimum oil flow requirement through the fan drive motor.

ACTIVATING THE HYDRAULIC FAN WITH THE SCAN TOOL

Under the Engine Systems test heading, there is a subheading. "Hydraulic fan solenoid test", that has the selections, on/off. Activating the fan with the scan tool will run the fan at 100% duty cycle, which will help troubleshoot any system problems, and also help with the deaeration procedure.

NOTE: Engine must be running to activate the fan with the scan tool.

RADIATOR COOLING FAN HYDRAULIC FLUID PATH

Hydraulic fluid is pumped through the power steering pump, from the pump the fluid travels though a high pressure delivery line to the fan drive motor. As fluid is diverted through the G-rotors, rotational motion is created as fluid moves from the high-pressure (inlet) side of the motor to the low-pressure (outlet) side. Fluid exiting the drive motor is divided into two paths. Path one continues through a high pressure delivery line to the vehicles steering gear to provide steering assist. and path two sends fluid back to the power steering pump through a low pressure line. Fluid exits the steering gear under low pressure and travels through a low pressure line to the power steering fluid cooler to be cooled before being returned back the power steering fluid reservoir.

NOTE: There is a steering flow control valve located in the fan drive motor. This valve operates like the flow control valve found in the typical power steering pump. Because of the design of the valve steering assist can not be effected by the radiator cooling fan even during fan drive failure.