How To Test And Replace A Car Radiator’s Relay Switch

The heat of summer puts extra pressure on your car's radiator system to keep your car engine cool. Eventually, parts will start to wear out and the system will stop working. Your car will begin to overheat shortly thereafter. A major reason some cars overheat during the summer is because the radiator fan stops working, and it isn't able to cool down the coolant in the radiator. There are numerous reasons why this can happen, but one of the easiest to fix is a blown relay switch. Here is how you can test the relay switch to see if it's working and how you can replace a bad one.

Testing the Relay Switch

The relay switch is usually located in the fuse box. Most fuse boxes have a diagram on the underside of the top covering the fuses. You can check the diagram to see which relay switch goes to the radiator. You need to pull out the switch to test it. Here are a couple of ways to conduct the test.

The quickest way to test the relay switch is by using your car's battery. Take two lengths of regular wire of different colors and put alligator clips on both ends of them.

Connect one wire to the negative terminal on the car battery, and place the other end of the wire onto one of the terminals on the relay switch. Connect the alligator clip of the other wire to the positive terminal on the car battery. Take the wire attached to the positive battery terminal and touch the clip to the other terminal on the relay switch (make sure the wires don't touch each other so they don't start sparking). If you don't hear a clicking sound coming from the relay switch, you'll need to replace it.

If you don't have wires or alligator clips, you perform a test that takes longer than the first one. Take one of the other relay switches in the fuse box that has the same amperage and put it into the spot for the relay switch for the radiator.

Start the car and let it run until it heats up enough to kick on the fan. If the fan kicks on after a little while, then you know the old relay switch is bad.

Replacing the Switch

Take the old relay switch with you to the auto parts store. The store's attendant can use it to pick out a comparable replacement one for your radiator. Take the switch back home and plug it into the fuse box to restore power to your radiator fan.

If you want help with this process, or if it doesn't seem to fix the issue, you can take your car to a local auto shop like City Radiator Service Ltd