Cooling Fan - Transit
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2018 Ford Transit-350 HD, 2018 Ford Transit-350, 2018 Ford Transit-250, 2018 Ford Transit-150, and 2018 Ford F-550 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
The primary cooling fan is a mechanical fan driven by the engine. The fan speed is relative to the engine RPM depending on the ambient air temperature.
The secondary cooling fan is electric and controlled by the PCM. The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C ON/OFF status, A/C pressure) to determine engine cooling fan needs.
The PCM controls the secondary fan operation through the low fan control (LFC), high fan control (HFC) outputs.
The PCM output circuits are called low and high fan control, and the secondary cooling fan speed is controlled by a combination of these outputs.