General Description
The auxiliary electric
cooling fan consists of the following components:
| • | The radiator support (2) |
| • | The auxiliary cooling fan assembly |
The auxiliary electric cooling fan provides additional cooling for the
following conditions:
| • | Low speed vehicle operations |
| • | Running the air conditioning system |
Operation, Gasoline Engines
The auxiliary cooling fan on L29 engines is controlled by the VCM based
on the following inputs:
| • | 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 ECT, 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 the
coil 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. Because 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
in order 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.
