Theory Of Operation-Cooling Fan System

The Promaster (VF) Radiator Cooling Fan System differs dependant on whether it is equipped with or without Air Conditioning. Both systems have three control circuits to operate the fans in low speed or high speed modes. The Powertrain Control Module (PCM) performs fault detection on the control circuits. The diagnostic for the control circuits is designed to detect a faulty relay as well as an open or shorted condition on the control circuits. Both configurations have two relays inside the Power Distribution Center (PDC) and an external Radiator Fan 1 High Speed Relay mounted on the Radiator Fan Assembly. Vehicles equipped with A/C have a second external relay mounted on the Radiator Fan Assembly (Radiator Fan 2 High Relay) which is used to control the high speed operation of Radiator Fan 2 Motor (right).

There are two main differences between the two configurations:

On vehicles equipped without A/C, the Low Speed Relay in the PDC is energized to operate Radiator Fan 1 Motor (left) on low speed while also supplying voltage to the Radiator Fan 1 High Relay. On vehicles equipped with A/C, the Low Speed Relay is only energized to operate Radiator Fan 1 Motor on low speed. The Radiator Fan 1 High Relay is supplied voltage directly from fused B+.
On vehicles equipped without A/C, the Radiator Fan 2 Relay in the PDC is only energized to operate Radiator Fan 2 Motor on high speed. On vehicles equipped with A/C, the Radiator Fan 2 Relay is energized to operate Radiator Fan 2 Motor on low speed while also supplying voltage to the Radiator Fan 2 High Relay mounted on the Radiator Fan Assembly.

NOTE:

It is important to know that on a vehicle equipped with A/C, the PCM uses the Low Speed Fan Control circuit to control the Radiator Fan 1 Relay and the Radiator Fan 2 Relay simultaneously. Therefore, in order for a fault to set due to a faulty relay or missing voltage supply to the relay coil, both relays must be faulty or missing the voltage supply to the coils. If either one of the relays is functional, the Cooling Fan 1 Control circuit fault will not set. This could cause a cooling fan to be inoperative at low speed without a DTC present.