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Home >> Jeep >> 2007 >> Commander Base, 4.7 P, AWD >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Engine & Automatic Transmission Cooling System >> Engine >> Fan-Radiator >> Operation >> Operation - 5.7L/3.0L Diesel >> Hydraulic Fan Strategy

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:

  1. Engine Coolant Temperature
  2. Transmission Oil Temperature
  3. 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.
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