General Description
The auxiliary electric cooling fan consists of (1) radiator support (2) wiring harness (3) bolt/scew (4) auxiliary cooling fan assembly and provides additional cooling for low speed vehicle operations, extended idle, stop and go conditions, and running the air conditioning systerm.
Operation, Gasoline Engines
The auxiliary cooling fan on L29 engines is controlled by the VCM based on the following inputs:
| • | The A/C system |
| • | The Engine Coolant Temperature (ECT) sensor |
| • | The Vehicle Speed Sensor (VSS). |
The VCM will turn the auxiliary cooling fan ON when any of the following conditions exist at idle:
| • | Certain VCM Diagnostic Trouble Codes (DTCs) are set. |
| • | ECT above 107°C (225°F). |
| • | A/C head pressure above 225 psi. |
Once the auxiliary cooling fan has been turned ON by the Engine Coolant Temperature (ECT) sensor, the VCM will turn the fan OFF when that temperature has dropped about 4°C (7°F). If the auxiliary cooling fan has been turned ON by high A/C head pressure, the VCM will turn the fan OFF when the pressure has dropped to 180 psi. The minimum ON time for the auxiliary cooling fan is 50 seconds.
Voltage is supplied through the ENG-BAT fuse to the auxiliary engine coolant fan relay (coil side). Ground is supplied through the A/C high pressure fan switch to ground G200. The VCM provides the ground path which will turn on the coolant fan. Whenever the coil is grounded it becomes energized, closing the contacts of the relay. Battery voltage is provided to the engine coolant fan motor through the closed contacts of the relay. Since the engine coolant fan motor is grounded at ground G200, the motor turns and operates the fan.
The L31 and L35 gasoline engines do not have an auxiliary cooling fan.
Operation, Diesel Engines
The auxiliary cooling fan is operated directly by an A/C pressure switch on Diesel Engines. The L65 engine also has an engine coolant temperature switch to operate the auxiliary cooling fan.
The ENG-I fuse supplies voltage to the auxiliary engine coolant fan relay (coil side) when the ignition switch is in the RUN or START position. Ground is supplied through the auxiliary fan control A/C high pressure switch to G200. The engine coolant temperature switch in the L65 engine is grounded directly. Grounding the coil energizes the relay, closing the contacts of the relay. Closing the contacts of the relay provides battery voltage to the auxiliary engine coolant fan motor. The auxiliary engine coolant fan motor grounds through G200 and operates the fan.
