Electric radiator-fan motors are turned on either by the ignition switch and will continue rotating while the engine is working – or by a thermostatic switch.
Motors controlled by thermostat do not signal the fan to run until the engine rises above normal operating temperature, and would then switch off the fan when it has cooled down again.
To ascertain if the fan is working, listen for it cutting in and out, and be checking the temperature gauge.
However if the engine shows signs of overheating, pull over and look to see if the fan is functioning. When checking for this, be sure to keep your engine running if your car is operated by the ignition switch.
But where there is a thermostatic switch in the circuit, keep the car on and let it run at fast idle. Without air flowing through the radiator, it will soon warm the engine up to the temperature at which the fan should start fanning.
The fan assembly usually has but three components – fan motor, thermostatic switch, and relay. If the fan is not working, the faults may be from these units and or the wiring to them may be faulty… Here are steps on how to repair the fault
Ø INSPECTING THE CIRCUIT AND MOTOR FOR FAULTS
Check the fuse box for any blown fuse. If the fuses are ok, turn on the ignition and use a circuit tester to confirm if there is current at the motor terminals.
Otherwise you connect the feed terminal on the motor direct to the battery positive terminal if it is the kind of motor that is fed through a thermo-switch.
In either case, if there is a current at the motor then the motor is faulty.
But if the thermo-switch fails to operate, the earthling point of the circuit may be at fault. Confirm that the earthling point is clean and tight. Check also the working of the thermo-switch.
Ø REPLACING THE FAN MOTOR
Remove the battery terminals and take remove the wiring terminals to the motor or disconnect the plug. Remove the wires from clips or other fixings on the fan shroud or nearby bodywork.
The motor and fan component normally come as an assembly, but most times the shroud may have to be removed and sometimes the radiator.
Separate the parts. Clean the parts that are to be reused by degreasing or even repainting.
Checking the new motor
When you fit a new motor, make it by connecting its leads directly to the battery. Be sure to connect the proper polarities, i.e the positive (+) and negative (—) leads to the corresponding terminals.
Be carefull as the motor will kick as it starts and there will be a large spark upon connection
If the fan motor is not at fault, leave the ignition switched on, take the connections off the thermo-switch and briefly touch them together.
If the fan motor now works, the switch is faulty. If it does not, check to see that there is current flowing to the switch by using a circuit tester on the supplied wire to the thermos witch.
Touch the leads together to bypass the switch.
If the tester does not indicate, trace the lead from the thermo-switch back to its power supply and where in doubt please consult the car handbook for a wiring diagram.
If the tester comes up, trace the lead through the thermo-switch through to the relay and confirm that the terminals are tightened and clean. These is very important.
- REPLACING A THERMO-SWITCH
The thermostatic switch is usually located in the radiator bottom tank, in the thermostat housing, or in the cylinder head area.
To do this, remove the switch, try flushing the radiator until the coolant is below the level at which it is fitted. Put the coolant in a clean container if you plan to reuse it.
If a rubber cover is used over the back of the switch, take it off, and disconnect the electrical connections.
Use appropriate spanner to unscrew the switch from its mounting point. Point to note is that unscrewing may, however, be very tight, so be careful not to damage the surrounding metal if it is fitted in the radiator bottom tank. And remember to fit a new sealing washer.
- INSPECTING THE RELAY FOR FAULTS
Try short-circuiting the thermo-switch terminals to test if the relay is faulty. Plan to withdraw the lead connectors partly to bare the terminals.
With the ignition turned on, short-circuit the thermo-switch by putting a screwdriver across its two terminals. Do not disconnect the leads. You should hear a click from the relay as it operates.
Use a tester to test for current with a test lamp or circuit tester at the live lead to the relay doing this with the ignition turned on.