K 3500 Truck 4WD V8-5.7L VIN R (1998)
Accessory Signal: Description and Operation
Description
Description
DESCRIPTION
The auxiliary electric cooling fan consists of (1) radiator support (2) wiring harness (3) bolt/screw (4) auxiliary cooling tan assembly and provides
additional cooling for low speed vehicle operations, extended idle, stop and go conditions, and running the air conditioning system.
OPERATION
The auxiliary cooling fan is controlled by the VCM. The VCM controls the ground path for the cooling tan relay. The relay consists of (1) under hood
fuse relay center (2) auxiliary cooling fan relay (3) wiring harness and is used to control the high current flow to power the cooling fan motor. The
VCM determines operation of the independent fans based on various sensor inputs.
The auxiliary cooling fan 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.
