2 of 2

Chart C-12 (2 of 2):

Wiring Diagram For Cooling Fan With A/C:

Relay Component Location:

CIRCUIT DESCRIPTION:

The radiator cooling fan will run on low speed any time the A/C compressor clutch is engaged. Battery voltage is applied to terminal "86" of the low speed fan relay, through the A/C compressor clutch relay. This closes the relay and completes the circuit as follows: from the number 14 fuse, to circuit 440, to the relay, through circuit 340, to the .6 ohm resistor, and the fan motor. The high speed cooling fan relay is ECM controlled. The ECM will ground circuit 939, which actuates the relay. Once this occurs, the high speed fan motor circuit completes as follows: from the number 14 fuse, to circuit 440, to the relay, through circuit 903, to the fan motor. The ECM will run the fan at high speed if the following sets of conditions are met.

Condition 1
a. Malfunction Codes 14 or 15 are present.

Condition 2
a. Engine coolant is greater than 107°C (224°F).

Condition 3
a. Engine coolant is between 26°C and 107°C (79°F and 224°F).
b. Vehicle speed is less than 44 mph.
c. High pressure blower switch closed.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

4. Whenever the A/C clutch is engaged, the cooling fan should be running on low speed.
5. As long as the high pressure fan circuit is not defective or the engine is not overheating, the ECM should not command the fan to run in this step.
6. If insufficient cooling is the complaint, it may be caused by the high pressure fan switch circuit not operating properly. This would indicate to the ECM to power the high speed cooling fan. The "Scan" tool should indicate the fan is requested before the A/C high pressure switch opens (see the wiring diagram in CHART C-10 or see ELECTRICAL AND ELECTRONIC DIAGRAMS). If the high pressure fan switch does not close, check for an open or short to ground in circuit 901 before replacing the switch.


DIAGNOSTIC AIDS:

1. If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, the temperature light, or the temperature gauge indicates overheating.
2. If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a Scan tool and comparing its reading with the gauge reading.
3. If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not energized, the coolant sensor has probably shifted out of calibration and should be replaced.
4. If the engine is overheating, and the cooling fan is running, the cooling system should be checked.