01446678004 | Broad Street, Barry CF62 7AH | Open: Mon-Fri: 8:30 - 5:30pm Sat: 8:30 - 12:30pm Sun: Closed hello@ijpautomotive.co.uk

It’s quite easy to recognise your car overheating when AC is on, however, drivers often don’t know the reasons why so they quickly jet off to the auto repair shop for advice. This article will save you that trip to the auto repair shop, by providing you with the 6 main reasons and fixes.

However, the surprising thing is that many car owners will go straight to the car mechanic or a professional to spend hundreds of pounds just to find out a very simple way in which their car overheats when AC is on.

If your car overheats when the ac is on and idle, you should not worry because you will also find a simple solution for that. Let’s get into it!

What Are the Symptoms of a Car Overheating When AC Is On

You may be wondering what the symptoms of a car overheating are when the AC is on. There are some common signs which will tell you your car is overheating when AC is on.

Here are the most common signs to look out for of a car overheating when AC is on:

  • Hot car interior
  • Car temperature gauge
  • Car engine shuts down
  • Cloud of steam from under the hood

Hot Car Interior

If your car’s interior components get hot, you will be able to feel it and this is a great indication that the car is overheating with the AC on. You may be able to notice a burnt smell coming from the car or air conditioning, a sign of the ac causing car to overheat.

Car’s Temperature Gauge

Reading a car’s temperature gauge is a handy way of telling whether your car heats up when ac is on. Your car’s temperature gauge will measure the temperature of the engine’s coolant.

On average, the temperature should be somewhere between 75 degrees and 105 degrees. If you see your car’s temperature gauge reading higher than 105 degrees, this is a serious sign of the car overheating with AC on.

Car Engine Shuts Down

Your car will likely automatically shut down if it overheats, no matter the cause. When you turn the car’s AC on and suddenly the car engine shuts down, this will indicate you have a problem with the car’s air conditioning system, which causes the car runs hot with ac on.

Cloud of Steam From Under the Hood

One of the easiest ways to know your car is overheating is via a cloud of steam coming out from under the car’s hood.

Whenever you see clouds of steam coming out from under the hood, you should conduct necessary checks for car overheating issues.

These are the most common and useful symptoms which tell you if your car overheats when AC is on. Before taking any steps to your overheating car with AC on, you have to be certain about the reasons your car is overheating.

6 Common Reasons for a Car Overheating When AC On

If you are to notice your car engine dashboard and seats are overheating after a few minutes of the air conditioner being turned on. Or, if your car overheats when idle and AC is on, you should generally check the AC compressor, the condenser, and the water pump immediately.

A car running hot with ac on is a very common issue around the world for all makes and models of car. Here are the 6 most common reasons why car overheating with ac on:

  1. AC Compressor Overload
  2. Issues with Radiator
  3. Defective Engine Coolant Sensor
  4. Faulty Fan
  5. Bad Cooling System
  6. Faulty in-vehicle Components

Let’s take a look at each in more detail!

1. AC Compressor Overload

Probably the most common reason why a car overheats when AC is on is the AC multifunctioning compressor overloading. After turning the air conditioner on, the compressor begins to work with the engine, to move the refrigerant cylinders to compress, which creates great pressure on the engine.

The compressor is generally the backbone of the car’s air conditioning system. The compressor’s main job is to increase the pressure of the refrigerant. A failing ac compressor would not be able to do the job correctly, leading to issues with the AC unit.

The ac compressor draws power from the output shaft of the engine. When the compressor goes bad, it puts a rotational load on the engine shaft. This increased engine load will be the foundation of an engine overheating.

As we already know, the car air conditioning system draws a significant amount of power from the car engine. If a high load is put on the compressor that it is unable to handle, it will not only damage the AC compressor but also eventually lead to your car engine overheating and preventing the AC from blowing cold air.

When a car engine overheats, the whole car will overheat in a short amount of time.

2. Issues with Radiator

The radiator has a significant role in helping pass the coolant into the engine. Vehicles operate properly when the radiator is able to pass the coolant through the metallic fins to the engine effectively.

However, the radiator work can be disrupted at any time, which will ultimately lead your car to overheat when ac is on. It’s advised to check the radiator when you notice your car getting overheated when you turn on the air conditioning, as you could have a faulty radiator or non-functioning metallic fin in your car!

3. Defective Engine Coolant Sensor

Defective engine coolant temperature sensors are not the most popular reason for a car overheating with AC on, but it is still possible. The coolant temperature sensor’s job is to keep track of the engine’s operating temperature.

The ECM (Electronic Control Module) will then use this information along with outside air and intake temperatures in order to determine critical engine parameters for the vehicle. The ECM will not be able to properly function without the engine coolant temperature sensor.

Therefore, if the engine coolant temperature sensor becomes defective, it will report the wrong coolant temperature to the ECM. And then, the coolant system is compromised, and you will likely experience the engine overheating and the car overheating when ac is on.

To fix the defective engine coolant’s temperature sensor issue, you may need to go to a professional mechanic, unless you’re able to replace it yourself.

4. Fault Fan

Cooling fans are able to ensure the smooth heat transfer between the engine coolant and the outside air. When the cooling fans of your vehicle are not functioning properly, you will undoubtedly experience overheating problems.

A faulty engine fan is another very common cause of the engine overheating when ac is on. The car ac system will put extra strain on the engine, and as a result, the heat will be generated at far higher rates.

The coolant system will then need to work even harder to remove this excessive heat. The chances of a car overheating are multiplied when components like the cooling fan become faulty.

The blades of the fan may have become distorted, or the fan switch that is responsible for turning on the fan might have become faulty. There are multiple possible fan faults, and even the possibility of the cooling motor being the culprit.

If the engine fan is clogged or bad, it will be unable to blow the cool air to the engine to stop it from overheating.

5. Bad Cooling System

The cooling system plays a very significant role in an AC system. Its job is to keep the air conditioning condenser cool when the air conditioner is heating up.

If your car cooling system is clogged, the condenser temperature will rise, leading to the car overheating when AC is on.

The cooling system can become faulty due to any of the following reasons:

  • Dirty AC system – may become dirty and lose efficiency in terms of heat transfer from the coolant to the outside air.
  • Failing AC relay – controls when the AC (Air Conditioner) system operates and can cause the system to work intermittently or not at all.
  • Failing thermostats – may fail open or closed, causing your motor to run hot, leading to overheating.
  • Leaks in the radiator – impacts from stones and debris can cause leaks with the same impacts as those with leaking radiator hoses.
  • Leaking radiator hoses – will reduce the amount of antifreeze fluid in the system, causing the system to work less efficiently as well as endangering your engine components, including the water pump.
  • Water pump failures – failed bearings and corroded components can lead to reduced efficiency or even complete failure of the pump.

Remember: clogging is another devastating issue in the car. The radiator and condenser in the car may help you to figure out why your car overheats.

6. Fault In-Vehicle Components

The fault components in your car can cause your car to overheat when AC is on. If the compressor, condenser, evaporator, and refrigerant do not work properly or as they should, the pressure gets into the air conditioner and the car temperature will increase.

To avoid these issues, you should be checking these components regularly and making sure that they all work efficiently. You should be wary of any minor fault in components as they can cause you problems in your car.

Whenever you take your car to a car mechanic, it’s worth having your car’s components checked to ensure they’re efficiently working.

The 6 issues presented are the most common reason why your car overheats when the air conditioner is on. Many people will ask about a specific model or brand of car’s overheating issue when ac is on. Most cars have a similar air conditioning system, and therefore, these reasons will apply across the board.

How to Fix a Car Overheating When AC is On

Repairing the car’s components or engine is likely to be an expensive solution. Due to the car air conditioner system issue causing the engine to overheat, repairing a car engine is not the ideal solution.

Instead, you can take the following steps to try fix a car overheating when AC is on:

  • Clean the radiator
  • Add water to the radiator
  • Check AC compressor
  • Check the refrigerant
  • Check the condenser
  • Check the coolant mixture
  • Flush the coolant system

Let’s take a look at each solution in more detail!

Clean the Radiator

The radiator is crucial in an engine’s cooling system. If your car’s radiator has been clogged, the radiator cannot pass the Antifreeze and water continually.

Try to check the radiator and aim to clean the radiator regularly. It is recommended to clean the radiator’s internal pipes with suitable tools.

Add Water to the Radiator

The radiator typically needs water in order to operate properly. If you see that the radiator is dry, then you should add water to the radiator. The water pump in the car takes water from the radiator and moves it through the motor back to the radiator, where the cycle begins again.

So, if there is a lack of water in the radiator, the cycle won’t work as it should, and the car will overheat.

Check the AC Compressor

The AC compressor may be the main culprit when it comes to an issue with car air conditioners overheating. If you hear any weird noises from the AC compressor, you should conduct a check on the AC compressor properly. 

Check the AC compressor’s wire and check the proper voltage. Of course, you will need to check for damage and the clutch in the AC compressor.

Check the Refrigerant

The refrigerant is an essential ingredient for your car’s air conditioner to operate. You should aim to maintain a sufficient amount of refrigerant in the car that can rescue your car from overheating when ac is on. You must check this frequently.

It’s also crucial to use the right refrigerant. Many car owners will use the wrong types of refrigerant in the car, ultimately causing your car to overheat with ac on.

Check the Condenser

The car air conditioner condenser is a radiator positioned between the car’s grille and the engine cooling radiator. Check the AC condenser first.

If you see your car’s AC condenser is clogged or blocked, it will not work properly and will cause your car to overheat. You must clean the condenser right away.

Change the Coolant Mixture

Coolant, also referred to as Antifreeze, is a coloured liquid that is mixed with water to help regulate your car engine during extremely cold temperatures.

Antifreeze also helps to prevent corrosion in your car and increases the durability of your car. You should change the coolant at least every two years.

Flush the Coolant System

By flushing the coolant system, you may be able to fix the car overheating with ac on issues in your car. You should regularly check the coolant system.

What to Do if Car Overheats With AC On in Traffic

Surprisingly enough, I experienced this in my life. Being stuck in traffic is always stressful and irritating. Also, the car overheats with AC on in traffic. This is worse than anything, I guess. What do you think?

Here is a step by step guide for what should you do if your car overheats with ac on in traffic:

What to do if car overheats with ac on in traffic

  1. Pullover vehicle

    First, pull over as soon as possible. Unfortunately, many times and in many places, you will not be able to pull over the car so easily.

  2. Turn off the car air conditioner

    Turning off the car air conditioner might help your car engine cool a bit. But, it would be best if you can turn off the car completely after parking and neutralize the car in a safe place.

  3. Open your car hood

    If your car’s hood is so hot and you can’t even touch the hood, you should wait until it cools down. After your car hood gets cold, you can open it, and hopefully, the steam will be gone.

  4. Turn off the car engine

    Turn off the car engine but keep the key in the ignition. This will keep the fan running. If you notice the fan doesn’t work or is not spinning as it should be, the fan may be the main culprit for the car overheating.

  5. Wait for roughly 30 minutes

    Your car air conditioner should cool down within 30 minutes. When your car engine is cold, you need to check and search for any leakages in your car. Otherwise, you may be good to start the car again!

It may be worth getting a professional to inspect your vehicle if the information in this article doesn’t help you diagnose and solve your problem.

FAQs (Frequently Asked Questions)

Why does my car overheat when the ac is on?

Your car is overheating likely due to AC compressor overload, issues with the radiator, defective engine coolant sensor, a faulty fan, faulty cooling system, or faulty in-vehicle components.


Please leave a comment below if you have any questions regarding your car overheating when ac is on!