Why Does My Car Overheat When the AC Is On and Idle?

Overheating is the most common reason why engines get damaged. There are many reasons why your engine might be overhead and even more ways to diagnose the real problem. In this article, we’re going to talk about specific situations of why cars overheat when the A/C is on. Certain questions such as: “why does my jeep overheat when I turn the ac on?” or “please help me I cannot find the cause of the 2013 ford fiesta overheating when the ac is on” may pop up. This can be frustrating, so when experiencing any of the following symptoms, you have to stop and take immediate action in order to limit any further damage to your vehicle.

What are the Symptoms of a car overheating when ac is on or idle?

 The symptoms are the same as when a vehicle overheats without having the engine on  

Temperature gauge: Every car has a coolant temperature gauge that should not exceed 110 c. Additionally, there are cars that are equipped with warning temperature lamps instead of the traditional gauge. They are designed to turn on and warn you if there is an abnormal rise in engine coolant temperature. The only time these gauges do not work is when there is a coolant leak.

car overheating when idle Car feeling hot: If you feel that your car is physically hotter than before and you can smell burnt plastic or rubber, this can mean that your car has overheated and the gaskets and plastics are starting to melt. 

car overheating and ac blowing hot air

Ticking sounds coming from the engine compartment: When the engine oil gets used past its manufacturer-recommended time, it loses its viscosity and therefore does not do its intended job. This, in turn, will leave pats to create friction between them.

Engine shut down: Every single modern car has some sort of safety precaution put in place that won’t allow the engine to start if it has overheated regardless if the A/C is on or off. Once the car was cooled down, it can now be started again.

engine overheating

What are the reasons the car overheats when it’s idle and the A/C is on?

 So, you figured out that your car is overheating while sitting in traffic with the A/C on, now let’s figure out what is causing that issue. 

car overheats when heat is on

AC compressor overload: As we know, we operate the A/C the compressor puts extra load on the engine. You can notice this by turning on the A/C and you will notice a slight increase in RPM. When manufacturers design the cooling system on a vehicle, they do so that it won’t cause running issues. Problems start to surface when the compressor ends up seizing and no longer being allowed to turn by the accessory belt. The car not knowing that will still try to turn that compressor, therefore, overheating the engine due to the additional strain put on it.

Defective cooling fan: Another reason that your car overheats when idle and AC is on may be caused by a malfunctioning cooling fan, cooling motor, or any connectors’ controls that activate the cooling fan. The cooling fan at different speeds for various loads (some cars are equipped with 2 fans) and each speed has a certain level of load to cool the engine. So, if the fan motor is weak, it won’t cool the motor properly, therefore causing the vehicle to overheat.

 **In some cases, a defective fan relay will cause the same issues. 

Bad cooling system: Checking the cooling fan is the first step of inspecting the cars. The next step is checking the rest of the A/C system because a healthy cooling system is everything. The cooling system works to cool down the condenser which is being heated up when AC is switched on. The main function of the condenser is to convert the cooling gas from a gaseous to a liquid state. In order to ensure this process is done correctly, the radiator shouldn’t have any clogs that may restrain the flow. Moreover, a bad water pump can lead to poor heat dissipation that will lead to your engine overheating with AC on.

Defective engine coolant sensor: As we know, the device that is responsible for signaling the engine control module to turn on the cooling fans. This sensor is located on the cylinder head in the water passages that measure the water temperature coming from the radiator to the internal parts of the engine. So, this sensor might be the reason why the engine overheats when the AC is on. Because this sensor may not be giving the right signal to the engine, The control module that is responsible for turning on the fans to the proper speed will not function.

How to fix the problems:

Repairing an engine overheating due to a defective AC system may be a bit confusing because it involves many parts, but also it’s not that hard because once you solve the problem, it’s gone forever and you begin to enjoy your ride once again. Here are some fixes that might help you resolve your issues:

car overheating after adding freon

  • First thing you should test the fan and auxiliary fan (if equipped). And test if it works at full speed when the AC is on. If the fan motor is in good condition, try checking the relay that is responsible for the AC fan.
  • Check the radiator for any clogs and obstacles that can block the flow. Additionally, try to get the radiator out every now and then and check it for leakage as well as clean the internal pipes with special tools and substances that dissolve any dirt and rust that may cause blockages.
  • Check the water pump for erosion on the internal fins. Damaged water pumps could cause serious problems to the engine by causing it to overheat.
  • To avoid any rust or corrosion in the radiator, water pump, or even the internal engine parts, you should change the coolant every 40.000 km or 2 years with a recommended type; and concentration, and always avoid using tap water as it contains salts and corrosion causing substances.
  • If your car is overheating after adding freon gas, it may mean that the type of this gas freon used is not compatible with your compressor. This can put a huge load on the compressor that may lead to damage to the A/C compressor. In the worst-case scenario, it may lead to your car overheating when A/C is on. The compressor would overheat and would blow hot air through your vents as opposed to cool air.

Car Engine Overheats While Sitting In Traffic, At Idle, or With A/C on YouTube Video

Final Words:

We recommend that you always check your cooling system as part of your periodic maintenance. This will prevent you from having bigger problems down the road. The engine’s first enemy is heating because it can damage the internal parts. This guide should help you fix the problem, but if you feel confused even a little, you should have an expert look at it.

Read More:


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Posts