Radiator Cooling Fan Motor: Description and Operation

On models equipped with electric engine cooling fans, the battery ground cable should be disconnected whenever underhood service is performed.




1985 BUICK SKYLARK & CHEVROLET CITATION

SYSTEM DESCRIPTION
The cooling fan located between radiator and condenser cools both engine coolant and A/C refrigerant. The fan is controlled by the cooling fan relay (located on LH side of engine compartment) which in turn is controlled by the coolant temperature fan switch (located on front of engine left of exhaust manifold on 4-151 engines; top of engine left of carburetor on V6-173 VIN X engines). The coolant switch closes at temperatures above 230 degrees F. On vehicles equipped with air conditioning, the relay is energized when the A/C is operating in certain modes. The relay is also energized under certain conditions when the A/C high pressure switch (located on compressor) closes at pressures above 280 psi. The switch then re-opens when pressure drops below 180 psi.
Models Less A/C
With ignition switch in RUN position voltage is applied through C-H fuse to cooling fan relay coil. Voltage is applied at all times through fusible link C (located at front of engine at starter solenoid) to cooling fan relay contacts. When coolant temperature fan switch is closed, circuit through C-H fuse, relay coil, and switch is completed to ground. This causes relay contacts to close, thus completing circuit through fusible link C, relay contacts, and cooling fan motor to ground, causing fan to run.
Models W/4-151 & A/C
When vehicle speed is below 35 mph, the ECM (Electronic Control Module, located behind RH side of instrument panel) grounds fan relay circuit. Current can flow in this circuit under either 1 of 2 conditions:
1. When high refrigerant pressure causes the A/C high pressure switch to close, the circuit is completed through C-H fuse, relay coil, A/C high pressure switch, and ECM to ground. This causes relay contacts to close and fan to run.
2. When A/C selector lever is set to MAX, NORM, or BI-LEVEL, circuit is completed through C-H fuse, relay coil, dark green/white wire, A/C selector switch, and ECM to ground. This causes relay contacts to close and fan to run.
Models W/V6-173 VIN X & A/C
With ignition switch in RUN, voltage is applied through C-H fuse to cooling fan relay coil. Voltage is always applied through fusible link C (located at front of engine, at starter solenoid) to cooling fan relay (located at front side of LH strut tower) contacts. Current can flow in this circuit under 2 conditions:
1. When coolant temperature fan switch closes, it completes circuit through C-H fuse, cooling fan relay coil, and coolant temperature fan switch to ground. This causes relay contacts to close and fan to run.
2. When A/C high pressure switch closes at pressures above 280 psi, circuit is completed through C-H fuse, relay coil, dark green/white wire, and A/C high pressure switch to ground. This causes relay contacts to close and fan to run. When refrigerant pressure drops below 180 psi, switch re-opens and relay de-energizes.
Models W/V6-173 VIN W & A/C
With ignition switch in RUN position, voltage is applied through C-H fuse to cooling fan relay coil. Voltage is always applied from battery junction block to cooling fan relay contacts. Cooling fan relay is switched on by ECM which provides a ground path for relay coil to energize relay and close relay contacts. When refrigerant pressure exceeds 240 psi, cooling fan pressure switch grounds ECM input causing ECM to switch on cooling fan.

TROUBLESHOOTING
Cooling Fan Does Not Operate
1. Check C-H fuse.
2. Check fusible link C, located at front of engine at starter solenoid.
3. Connect wire from cooling fan relay coil (dark green/white wire) to ground-cooling fan should run.
Cooling Fan Runs Whenever Ignition Is In RUN Position
1. Check temperature switch, pressure switch, and related mechanical systems.
2. Check cooling fan relay.

COOLING FAN, REPLACE
1. Disconnect battery ground cable.
2. Disconnect wiring from fan motor and frame.
3. Remove fan assembly from radiator support.
4. Reverse procedure to install.