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Radiator fan only turns on when AC is on

By David Wardell | Updated: May 21, 2022

Radiator fan only turns on when ac is onIf the radiator fan only turns on when the car’s AC is turned on, there may be a problem with the car’s cooling system. The cooling system is one way that the car’s engine stays cool. The thermostat is supposed to turn the fan on when the car’s engine gets too hot.

If the fan only turns on when the AC is turned on, it may be because the car’s thermostat is not working properly.

This can be a serious problem because it can cause the car’s engine to overheat. If the car’s engine overheats, it can damage the car engine and cause it to break down.

Contents

  • What if the radiator fan only turns on when my AC turns on?
  • The radiator fan only turns on when the AC is on: the common reasons
    • Faulty thermostatic switch
    • Fan resistor not working
    • Temperature sensor faulty
    • Faulty fuse
    • Wiring issues
    • Obstructed coolant flow
    • Radiator fan motor not working correctly
    • Clutch for motor fan
  • Conclusion

What if the radiator fan only turns on when my AC turns on?

There are a few things that could happen if the radiator fan is only turned on when the AC is turned on.

  • One possibility is that the car’s engine thermostat is stuck in a closed position. This prevents coolant from circulating through the engine, causing it to overheat.
  • Another possibility is that there is something obstructing the flow of coolant, such as a leak in the system or a blockage in one of the hoses. If the car overheats, it can cause serious damage to the engine. As a result, it is important to have the car inspected by a qualified mechanic to determine the cause of the problem.

Either way, it’s best to have a professional take a look at your car to diagnose the issue. In most cases, this isn’t a serious problem, but it’s always best to be on the safe side when it comes to your vehicle.

The radiator fan only turns on when the AC is on: the common reasons

One common question mechanics have is why a radiator fan only turns on when the AC is on. The answer has to do with how heat works. Parts of an engine get hot from friction and heat up the oil, which then needs to be cooled down. The water pump circulates water around the engine block to absorb heat, and the thermostat controls the temp. The radiator fan blows air over the radiator to cool everything down. When you turn on the AC, it blows hot air out of the car, making room for more cool air to come in and keeping everything at a stable temperature. So, if your radiator fan only turns on when the AC is on, that’s when it’s needed most.

There are a few reasons why your radiator fan might only turn on when the AC is on.

Faulty thermostatic switch

One possible cause is a faulty thermostatic switch that isn’t responding to engine overheating. This prevents the radiator from circulating the coolant and could lead to damage to other engine parts.

Fan resistor not working

There are a few reasons why your fan’s resistor might not be working. First, the resistor may have simply blown out. This is usually caused by an excessive build-up of dirt and dust on the blades of the fan, which puts increased strain on the motor. If this is the case, simply replacing the resistor should fix the problem. Another possibility is that the wires connecting the resistor to the motor have become frayed or disconnected. This can be caused by a number of factors, including age, vibration, or moisture. If this is the case, you’ll need to consult a professional to have the wires repaired or replaced. Lastly, it’s possible that the fuse protecting the circuit has blown. This is usually caused by an overload of electricity and can be fixed by simply replacing the fuse. Whatever the cause, it’s important to get to the bottom of the problem so that your fan can run smoothly and safely.

Temperature sensor faulty

If the temperature sensor is faulty, it can also cause your fan to only turn on when the AC is turned on. The sensor tells the engine when it’s too hot and needs cooling, so if it isn’t working properly, your radiator may not get enough coolant during periods of high heat. Luckily, it’s usually easy to replace a faulty sensor, and you can do so yourself if you have the right tools.

It’s important to get to the bottom of why your radiator fan only turns on when the AC is turned on. Depending on the root cause, this could be a minor or serious problem that needs immediate attention.

Faulty fuse

A common cause for this issue is a blown fuse that protects the circuit of your radiator fan. Fuses are designed to protect electrical devices from being overloaded, so if your fuse blows, it means you have too much electrical current running through the system. This can be caused by a number of factors, including age, vibrations from driving over rough terrain, or moisture buildup in the wiring.

Luckily, replacing a blown a fuse is usually simple and can be done by anyone with basic knowledge of electrical systems. All you need is a replacement fuse of the same amp rating as the broken one, some wire cutters to remove the old fuse casing, and a pair of pliers to crimp the new fuse in place. Once you’ve replaced the fuse, your fan should run smoothly and safely.

Wiring issues

If your fan’s resistor or the wires leading to it have become frayed or disconnected, this can also cause your fan to only turn when the AC is turned on. Wiring issues are usually caused by age, vibrations from driving over rough terrain, or moisture buildup in the wiring.

For wires that have simply become disconnected, you can often just reattach them to fix the problem. If wires have become frayed or damaged in any way, you’ll need to consult a professional who can properly repair your fan’s wiring system.

Obstructed coolant flow

Another common reason for a radiator fan only turning on when the AC is on is an obstruction in your car’s cooling system, such as a leak or blockage in one of the hoses. This can usually be attributed to one or more of a variety of different circumstances, such as contamination by external matter, dangerously low levels of coolant, or an older model that wasn’t designed with cooling fans in mind. Regardless of the reason for cooling fan failure, it is important to spot and address these issues as quickly as possible to ensure a safe and reliable driving experience. Whether you need to replace your cooling fan or simply give it a good cleaning and some routine maintenance, the key is to act promptly and proactively so that you are prepared for whatever point you may encounter on the road ahead.

Radiator fan motor not working correctly

A radiator fan is an essential component of a vehicle’s cooling system, and if it is not working properly, the engine can overheat. The most common symptom of a failing radiator fan is the engine overheating, particularly during stop-and-go driving or when idling in traffic. The fan motor may also make noise when it is failing. If the engine overheats, it can lead to serious damage, so it is important to have the problem diagnosed and repaired as soon as possible. In some cases, the radiator fan motor may need to be replaced. A qualified mechanic will be able to diagnose and repair the problem quickly and correctly.

Clutch for motor fan

If you are experiencing problems with your radiator fan motor, the first thing to check is the clutch for the fan motor. This component is what engages and disengages the fan when needed, based on the temperature of your vehicle’s engine and other factors. If this clutch is not working properly, it can cause your radiator fan to malfunction. In some situations, the clutch may need to be changed.

Conclusion

When the car’s thermostat is not working properly, it can be a serious problem, as it can cause the car engine to overheat and damage the engine. To prevent this from happening, you should have your cooling system checked by a professional electrician, and take care to maintain the clutch for your radiator fan motor. Taking these precautions will help keep your car running smoothly and safely. Thanks for reading! We hope this article has been helpful.

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About David Wardell

I am a technical specialist with over 14 years of experience in the automotive industry. I am well versed in the field of computer diagnostics and car repairs of various brands and models, so I can solve complex issues while providing quality service. Read More.

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