Circuit Operation

The Body Computer Module (BCM) controls both the LH and RH cooling fans, according to engine coolant and A/C refrigerant temperatures. The speed of the fans depends on whichever temperature calls for the higher speed. The BCM turns on both fans at approximately half speed when speed coolant temperature reaches 223°F (106°C) or refrigerant temperature reaches 122°F (50°C).

The fans run at high speed when engine coolant temperature reaches 241°F (116°C) or when refrigerant temperature reaches 162°F (72°C). The fans run until the engine coolant temperature is below 216°F (102°C) and the refrigerant temperature is below 115°F (46°C).

The BCM receives signals telling it what the coolant and refrigerant temperatures are. The high side temperature sensor, located between the condenser and the orifice tube, transmits the refrigerant temperature to the BCM. The ECM sends the coolant temperature through the data link to the BCM.

The BCM controls fan speed by sending a pulsing ON-OFF signal to the fan control module. The fan control module acts as an amplifier for the BCM control signal. This amplified control signal is then capable of powering one, or both, of the cooling fans at variable speeds.

The fan control module sends a signal back to the BCM through the feedback output. This signal tells the BCM whether the fans are turning or not turning. The fan control filter assembly filers out interference that the cooling fans might cause when the radio is playing.

With the ignition switch in RUN, current flows through fuse 7, the fan diode and the fan control relay coil to ground. The relay contacts close. Voltage is applied through fusible link E through the fan control filter assembly to the power input of the fan control module. The fan control module supplies a path to ground for the motors in response to the ON-OFF control signal sent from the BCM through the BRN wire.