Thermostatically Controlled Electric Fans
All electrically-driven fans are actuated by thermal relay switches. Thermal switches turn fan motor on when necessary and shut fan motor off when not needed. All air conditioned vehicles are equipped with over-ride switches. These switches turn fan motor on whenever air conditioning system is operating, and return fan motor control to thermal relay when system is turned off.
Although all electric fans operate on same principle, the following are special descriptions that apply to specific models
Scheme 1
Coolant temperature switch turns fan motor on at specified temperatures. Fan will also come on instantly when A/C is turned on. Fan motor shuts off when ignition switch is turned off, regardless of coolant temperature. The fan used on General Motors vehicles is 12" in diameter, made of plastic and has 5 blades.
Variable Speed Fans - Flex-Blade Fans
This unit is a fixed blade assembly designed to flex blades as engine RPM increases. As RPM increases blade pitch decreases, thereby saving power and decreasing noise level. No adjustment or test is required beyond keeping fan belt adjusted to proper tension.
Scheme 2
Variable Speed Fans - Fan Clutch W/ Thermostatic Control
Most air conditioned models use a thermostatically controlled fluid fan and torque control clutch. Thermal control drive is a silicone-filled coupling connecting fan to fan pulley, and is operated by a control valve. Control valve is operated by a temperature sensitive bimetal coil or strip and controls flow of silicone through the clutch.
During periods of operation when radiator discharge air temperature is low, the fan clutch limits fan speed. High radiator discharge air temperature causes bimetal to allow a greater flow of silicone to enter clutch. This increases drag between driven member and driving member resulting in a higher fan speed and increased cooling.
If fan is not operating properly, disconnect fan motor wire connector and connect it with 14 gauge wire to a good 12-volt battery. If fan runs, motor is all right, indicating car battery, coolant relay, coolant temperature switch, or A/C relay may be defective. If fan motor does not run when connected directly to a good battery, replace fan motor. See WIRING DIAGRAM .
Coolant Fan Relay Failure
General Motors FWD models may exhibit repeated coolant fan relay failure due to burned or sticking contacts. This may be caused by poor electrical connections, excessive fan motor currents or a chattering engine coolant temperature switch. To diagnose and repair, proceed as follows
- Check all electrical connections. Ensure that all electrical connections in the circuit are clean and tight.
- Check fan motor operating current. Fan motor continuous operating current should not exceed 20 amps on low speed or 35 amps on high speed. If current exceeds specifications, replace the fan motor.
- Check the coolant fan engine temperature switch using a test light. The light should be fully lit when the switch is closed. Check both the low and high speed positions of the switch. If the test light flickers in either position, the switch is chattering and should be replaced.
In cases of engine overheating or insufficient air conditioning proceed with following tests
Scheme 3
- Start with a cool engine to ensure complete fan clutch disengagement.
- Cover radiator grille sufficiently to induce high engine temperature.
- Start engine and operate at 2000 RPM. Turn on air conditioning if equipped.
- A fan roar will be noticed when fan clutch engages. NOTE: Shown with stamped face and bi-metal coil spring. NOTE: It will take approximately 5 to 10 minutes for temperature to become high enough to allow engagement of the fan clutch. While operating engine under these conditions, observe temperature light to prevent overheating. If hot light comes on, remove cover from radiator grille.
- As soon as clutch engages, remove radiator grille cover and turn A/C off to assist in engine cooling.
- After several minutes fan clutch should disengage. This can be determined by a reduction in fan speed and roar. If fan fails to function as described, it should be replaced.
WIRING DIAGRAMS
Note. For all models, refer to appropriate WIRING DIAGRAMS article.
Coolant Fan Wiring Diagram - DeVille & Fleetwood. Scheme 4
See also:
• WIRING DIAGRAM