Things You'll Need:
- Voltmeter
-
Step 1
Make sure the key is off. Switching relays is the fastest way to check for a bad relay when possible. A Jeep has more than one relay that are the same (go by the relay number on the top or side of the relay) in the fuse box on the driver's side fenderwell. Remove a known good relay and swap it with the radiator fan relay. Operate the vehicle and check the operation of the unit replaced. If the unit works with the fan relay it proves that the relay is not the problem.
-
Step 2
Test the relay using jumper wires and a voltmeter. Connect one jumper wire from the battery positive terminal to the relay positive terminal. Connect the second jumper wire from the negative terminal of the battery to the negative terminal of the relay. When the negative wire is attached to the relay, the relay should have an audible click as it activates. If the relay fails to click, move the jumper wires to the second set of terminals in the event the wrong terminals were being used. If the relay fails to click it is bad.
-
Step 3
Check the radiator fan switch if the relay proves to be good. If the fan switch is good, check the radiator fan by using the jumper wires from the battery to the electrical connection on the radiator fan to wire it directly to the battery. If it fails to operate the fan is bad.
