Umair Gaines
Testing an electric fan relay is a simple process that can help you identify issues with your vehicle's cooling system. The cooling fan relay is a critical component that activates the fan to cool the engine when it overheats, preventing severe engine damage. By following a few straightforward steps, you can isolate the issue to the relay or other potential causes. This involves checking the fuse, manually activating the fan, and using tools like a multimeter or ohmmeter to test for continuity. It's important to ensure the vehicle is turned off and follow safety precautions to avoid electrical issues and shock risks. With these tests, you can determine whether the relay requires replacement or if there are other underlying problems.
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What You'll Learn
- Check the fuse that controls the fan before testing the relay
- Bypass the relay with a jumper wire to connect the power terminals
- Unplug the coolant temperature sensor with the ignition on
- Use a multimeter to test the relay's terminals
- Inspect wiring to and from the relay for loose or corroded connections
Check the fuse that controls the fan before testing the relay
Before testing the relay, it is important to check the fuse that controls the fan. A blown fuse is a common cause of a fan not working, and it is simple to assess. First, locate the fuse, which is typically found in the unit's control board, often behind an access panel in the unit's lower compartment. Next, perform a visual inspection of the fuse. If there is a black flash mark visible inside the fuse or if its window appears obscured, it is likely blown. Alternatively, you can use a digital multimeter to test the fuse. Ensure the multimeter is working by touching the two probes together; if it makes an audible sound and shows an initial reading, it is functioning correctly. Place the probes on the fuse's specific connection points. If there is an audible sound and a similar digital reading to the initial one, the fuse is operational. However, if there is no sound, no reading, or a reading of "OL" on the multimeter display, the fuse is blown and needs to be replaced.
It is important to always use the correct amperage fuse as specified in your vehicle's manual. Using the wrong fuse can lead to severe electrical problems. If you replace a blown fuse and it blows again, the relay may be faulty. In that case, you can test the relay by having the car running and unplugging the coolant temperature sensor. If the fans come on, the relay or wiring is bad. Additionally, if your vehicle allows, try turning on the air conditioning to force the fan on. If the fan operates with the AC on, it confirms that the issue is isolated to the relay.
You can also bypass the relay as a temporary test by using a jumper wire to connect the power terminals directly. If the fan turns on, the relay is likely faulty. However, bypassing the relay should only be done for diagnostic purposes and not as a permanent solution, as it can lead to other electrical issues. If you have replaced the relay and continue to experience issues, consider testing the fan motor's current draw with an ammeter. A worn-out or internally faulty motor may cause the relay to overheat and fail. If the motor is drawing more current than specified, it needs to be replaced.
Additionally, loose or corroded connections can cause intermittent relay operation. Inspect all wiring leading to and from the relay, especially at the fuse box and fan motor. Corroded connectors can cause increased resistance, leading to relay failure. If corrosion is present, clean the connectors and apply dielectric grease to prevent future corrosion.
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Bypass the relay with a jumper wire to connect the power terminals
To test an electric fan relay, you can bypass the relay with a jumper wire to connect the power terminals directly. This method is a temporary test and should only be done for diagnostic purposes. It is important to ensure that the vehicle is turned off and the keys are removed from the ignition to prevent any electrical issues.
Firstly, locate the wiring diagram to identify the terminals on the relay. Then, pull the relay out of its socket, being careful not to pull on the wires connected to it. You may need a pair of needle-nose pliers if the relay is difficult to remove.
Next, take a stout piece of wire, at least 12-gauge and about 6 inches long, and crimp a male spade terminal to each end. This will serve as your jumper wire. Before making any connections, use a multimeter to measure the voltage at socket terminal 30 and verify that it is off. If it is not, wear gloves to protect yourself from any sparking or heating of the jumper wire.
Now, plug one end of the jumper wire into socket terminal 30 and the other end into socket terminal 87. If there is voltage present on terminal 30, you may see a small spark when connecting to terminal 87.
By bypassing the relay with the jumper wire, you are manually connecting terminals 30 and 87, which is the same function performed by the relay. If the fan turns on when the relay is bypassed, it is likely that the relay is faulty and needs to be replaced.
It is important to note that running the fan continuously without the relay can lead to other electrical issues. Therefore, this bypass method should only be used temporarily for diagnostic purposes, and the relay should be replaced if found to be faulty.
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Unplug the coolant temperature sensor with the ignition on
Unplugging the coolant temperature sensor with the ignition on is a way to test if a faulty fan relay is causing your car's fan to malfunction. Before attempting this test, check the fuse that controls the cooling fan. Replace a blown fuse and if the new fuse blows again, the relay may be faulty.
The coolant temperature sensor is usually a two-wire sensor mounted near the thermostat. When unplugged, the fan relay should close, and the fan should run continuously. If the fan comes on, then the relay or wiring is bad. If the fan does not come on, then the coolant temperature sensor may need to be replaced.
It is important to note that unplugging the coolant temperature sensor can disrupt the engine's ability to adjust fuel and ignition timing properly, leading to potential misfiring, rough idling, and poor performance. It is not recommended to leave the sensor unplugged for an extended period as it may cause damage to the vehicle.
Additionally, bypassing the relay by using a jumper wire to connect the power terminals directly is another temporary test. If the fan turns on, the relay is likely faulty. However, bypassing the relay should only be done for diagnostic purposes as running the fan continuously without the relay can lead to other electrical issues.
Overall, unplugging the coolant temperature sensor with the ignition on is a useful diagnostic test to determine if a faulty fan relay is causing the fan malfunction. However, it should be approached with caution as it can affect engine operation, and the sensor should not be left unplugged for an extended period.
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Use a multimeter to test the relay's terminals
To test a fan relay with a multimeter, you must first remove the relay from the relay box. Ensure that the vehicle is turned off and the keys are removed from the ignition to prevent any electrical issues. For safety, disconnect the negative terminal of the battery to eliminate the risk of electric shock or short circuits.
Now, set the multimeter to continuity mode and check the relay's terminals. If there is no continuity, the relay is faulty and needs to be replaced. You can also check for corrosion on the terminals, which can cause increased resistance and lead to relay failure. Clean the connectors with electrical contact cleaner and apply dielectric grease to prevent future corrosion.
As a temporary test, you can bypass the relay by using a jumper wire to connect the power terminals directly. If the fan turns on, the relay is likely faulty. However, bypassing the relay should only be done for diagnostic purposes and not as a permanent solution.
Additionally, you can test the voltage of the specific fuse protecting the fan circuit with a multimeter. However, this information may not be very useful, as voltage without current flow cannot do any real work. It is also important to note that using the multimeter in series with the fan will blow the fuse in the meter, so this should be avoided.
If you've replaced the relay and still experience issues, consider testing the motor's current draw with an ammeter. If the motor is drawing more current than specified by the manufacturer, it may be time to replace the motor as well.
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Inspect wiring to and from the relay for loose or corroded connections
When testing an electric fan relay, it is important to inspect the wiring to and from the relay for loose or corroded connections. This is because loose or corroded connections can cause intermittent relay operation and even lead to relay failure. Corrosion can cause increased resistance, resulting in relay overheating and eventual failure.
To inspect the wiring, start by removing the relay from the relay box. Be careful not to pull on the wires connected to the relay. Once the relay is removed, visually inspect the relay terminals for any signs of corrosion or damage. Use a small metal scribe or tool to gently scrape away any corrosion on the terminals to ensure a good connection once the new relay is installed.
Next, inspect all the wiring leading to and from the relay, including the connections at the fuse box and the fan motor. Look for any exposed or corroded wires, as this can raise the resistance enough to cause a voltage drop and affect the operation of the relay.
Additionally, you can use a multimeter to test for voltage drop across the wiring connections. Set the multimeter to DC volts and measure the voltage across the supply terminals. If there is a significant voltage drop, it may indicate a loose or corroded connection.
Another method to detect loose or corroded connections is by using thermal imaging. By capturing thermal images of the electrical connections, you can identify hotspots that indicate higher temperatures than similar connections under similar loads. These hotspots can signal high resistance due to loose or corroded connections.
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Frequently asked questions
Set the multimeter to continuity mode and check the relay's terminals. If there is no continuity, the relay is faulty and needs to be replaced.
Connect the leads of the ohmmeter to the power terminals on the relay. If you get infinite resistance from the ohmmeter, the relay contact points are not letting electric current flow through, and the relay should be replaced.
Separate the electrical connector that runs to the dual fans and provide a fused 12-volt jumper wire from the battery positive post. If the fans run, they are bypassed from the solid-state control.
Before testing the relay, check the fuse that controls the cooling fan. If the fuse is blown, replace it and see if the fan operates. If the fan doesn't turn on, the relay may be faulty. You can also try turning on the A/C to force the fan on. If the fan doesn't operate, the issue may be isolated to the relay.
