K 2500 Truck 4WD V8-5.7L VIN R (1996)
Radiator Cooling Fan Motor: Description and Operation
Circuit Operation
Auxiliary Cooling Fan operating Voltage is available at all times from the 30 Amp AUX FAN Mini-Fuse located in the Underhood Fuse-Relay Center.
Voltage is provided from the Fuse through the ORN (1540) wire which terminates at Pin 30 of the Auxiliary Cooling Fan Relay. When the Relay's Coil
is energized, Relay contacts close to apply operating Voltage to the Auxiliary Cooling Fan Motor. The RED (702) wire connects Relay Pin 87 to Motor
Pin B. The Motor is grounded from Pin A by the BLK (250) wire to Ground G112.
Voltage to the Auxiliary Cooling Fan Relay Coil is available when the Ignition Switch is in RUN, BULB TEST or START. Relay Coil Voltage is
supplied at Pin 85 by the PNK (639) wire from the 10 Amp IGN E Mini-Fuse located in the Underhood Fuse-Relay Center. The Auxiliary Cooling Fan
Relay Coil is energized whenever either of two potential ground paths is provided. The LT GRN (37) wire connects Pin 86 of the Relay to Pin A of the
Auxiliary Cooling Fan Temperature Switch and to the mode of Diode D100. Diode D100 enables current flow through the Auxiliary Cooling Fan A/C
Pressure Switch when the Switch operates to ground the Relay Coil.
When the Engine coolant reaches a set point, the Auxiliary Cooling Fan Temperature Switch closes the contacts. This provides a ground path from the
Auxiliary Cooling Fan Relay Coil through the LT GRN (37) wire and through the Switch contacts to ground at the Engine. The Temperature Switch
provides the ground connection at the Engine. The Relay Coil is energized, the contacts close, and the Fan Motor starts.
The Auxiliary Cooling Fan will also operate when the Auxiliary Cooling Fan A/C Pressure Switch operates in response to an increasing compressor high
side pressure. when the high side pressure increases to a set point, the Pressure Switch contacts close. This provides a ground path for the Auxiliary
Cooling Fan Relay Coil through the LT GRN (37) wire to Diode D100. Through Diode D100, through the LT ORN (1614) wire, trough the Pressure
Switch contacts and through the BLK (150) wire to Ground G105. The Relay Coil is energized, contacts close, and the Fan Motor starts.
Operation of the Auxiliary Cooling Fan A/C Pressure Switch can also affect the position of the Air Conditioning Recirculation Door. During normal
operation of the Recirculation Door, the A/C Controller places the door in the Recirculation position by grounding the Recirculation Door Motor. The
ground path is through the DK GRN (1614) wire from door Pin A to A/C controller connector C3, Pin 4. When the ground path is removed, the
Recirculation Door moves from the Recirculation Position.
When the Auxiliary Cooling Fan A/C Pressure Switch operates to start the Auxiliary Cooling Fan, it also provides another ground path for the
Recirculation Door Motor. If the Door Motor is not already grounded, it is now grounded from Pin 6 through the DK GRN (1614) wire, through Splice
S212, through Diode D101, through Splice S114, and through the Pressure Switch to Ground G105. The Door Motor operates to place the Recirculation
Door in the Recirculation Position.
Diode D100 prevents the Recirculation Door Motor from being grounded by the Auxiliary Cooling Fan Temperature Switch. Diode D101 prevents
operation of the Auxiliary Cooling Fan when the A/C Controller grounds the Recirculation Door Motor.
