Why is My Car Overheating When the AC Is On?

By Sheetal B. Updated: August 19, 2019
Why is My Car Overheating When the AC Is On?

Imagine you are driving on a hot summer day but suddenly your car starts overheating and you can’t use the AC. Not only would this be inconvenient as you swelter in a hot car, it could be causing some serious damage to the vehicle. Air-conditioning (AC) is one of the many features of a car to make commuting comfortable and is used almost always irrespective if the weather hot, cold, raining or snowing. However, if there is a problem with the AC, even normal usage can cause it to overheat. The way to find out how to fix it, is to first find out why does it happen. At oneHOWTO we explain the possible reasons why your car is overheating when the AC is on.


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Why is my car overheating?

There are several reasons why your AC is overheating your car and here are the most likely causes:

  • Inefficient functioning of the cooling system is one of the most common reasons for an overheated car. The reason for that could be as simple as a leak in the radiator which requires water to be refilled at short intervals. The tubes of the radiator (sometimes called the hose) corrode with time. Though the coolant has corrosion inhibitors added to it and help prevent such occurrences initially, over time it becomes ineffective. Take a look at your radiator and if you see a lot of built up dirt or debris, then this could be the cause of your overheating. You can easily wash the radiator by squirting a low pressure hose through the fins (do not use high pressure or it could cause damage). If the fins are bent, this can obstruct air flow, so carefully mold them back into shape with a flat-head screwdriver. If the fins are too damaged and rusted, then it may be time to get a new one.
  • It is very common for car to get overheated when at low speeds or when stationary in traffic when using the air-conditioning. This may also be due to lack of airflow through the radiator. If it is not a blockage in the fins, it may be that you need to fix a faulty electric fan assembly, fan clutch or fan switch.

  • The climate can cause the engine to overheat. Just because it is cold inside, doesn't mean it will be the same outside. However, it might be a combination of climactic heat and an issue with the coolant system. A healthy cooling system should avoid overheating even in very hot climates. However, a very hot day might exacerbate minor problems.

  • The leak may not be a problem with the tubes or hose. There maybe be a faulty connection somewhere in the cooling system. This can be a simple issue to resolve when buying a new part, but be careful in case the damage has already been done.
Why is My Car Overheating When the AC Is On? - Why is my car overheating?

What to do if your car overheats due to the AC

If you car overheats, the first thing you should do is turn the A/C off and pull over. While you will need to be careful, you should open up the hood and let the heat escape. Be careful to keep your face and eyes away from any steam. Let the engine cool before doing anything to it. Taking off the radiator cap can be very dangerous if the engine is overheated due to the AC.

Park the car and put it into neutral. Revving the engine can help you to release some of this excess heat, but don't do it too much in case there is some other damage to the engine. This is what you might be able to do if the engine overheats initially. However, this isn't the same as the longterm problem.

Sometimes, if an air-conditioning gas is not suitable for your particular type of vehicle, it can cause insufficient cooling. This gas is a refrigerant which acts to help cool the system. There are, however, different types of cooling mechanisms, so you need to ensure you have the right one for you. You can ask a mechanic to refill the refrigerant gas if you are unsure. You can do it yourself by removing the cap from the low pressure port and attaching the gauge. You will have to have the car running when you do this, so wear safety glasses and gloves. Refill the gas until the pressure is at the right level (it should show you on the gauge) and then refit the cap. Check the temperature from the AC vents before and after you refill the gas so you can tell if it has indeed made it cooler.

Air flow in the cooling system could also be a cause of your car overheating with the AC on. There may be insufficient air pressure in the radiator or even a blockage. Check this by setting an air pressure gauge on one end of the radiator and check the pressure. You'll need a special piece of equipment for this, so it may mean a trip to the mechanic if you don't have one or can't borrow one. It might be due to a faulty part which you can replace or be as simple as cleaning it out to regain the proper pressure.

Why is My Car Overheating When the AC Is On? - What to do if your car overheats due to the AC

Other reasons your car overheats

  • Another issue which causes the car to overheat thanks to air-conditioning is that you don't have enough coolant or anti-freeze in your system. Make sure you change your anti-freeze mixture every two years. This also helps to avoid corrosion in your system and will make the car last longer. There might also be air in the coolant system which has been trapped. As air will not cool the car engine as well as liquid, the trapped air will cause it to overheat. You may have to flush the system to fix the problem.
  • A malfunctioning thermostat might also be a likely reason for overheating while the car is running at a regular speed. This can also be caused by a damaged radiator, faulty radiator cap, lower level of coolant or a trapped air bubble in the system. Using a quality thermostat might really help your car.


Why is My Car Overheating When the AC Is On? - Other reasons your car overheats

My car is overheating while driving

If you face the overheating problem while driving, first stop the car, turn the heater on full blast so that the heat is pulled out from the coolant to the ambient air of the car. You might want to step out of the car when doing this. Next, turn off the AC. Idle the engine for a couple of minutes and then finally turn off the engine. Try and sort out any issue from the above pointers that can be fixed right away. If you are not able to do this, turn in the car to the nearest service center you can find. Needless to say, keep the AC switched off while driving to the service station.

To avoid overheating issues, there are few golden rules to follow such as:

  • Using the right coolant for the car model you own.
  • Using a superior quality thermostat.
  • Always using distilled instead of regular water.

For someone who’s not too much mechanically minded, just ensure to get your car serviced on time and look for early signs of overheating problems before it catches you off guard.

Take a look at how to recharge your car air-conditioning system at home or how to clean your fuel filter if you want to give your car a fresh start.

If you want to read similar articles to Why is My Car Overheating When the AC Is On?, we recommend you visit our Car Maintenance and Repair category.

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Jimmy Edwards
I have to drive my car with the heat on to keep it from over heating. What causes this
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