Car Overheats When AC is On: Symptoms, Causes and Fix Guide

There’s nothing wrong with driving your car in the summer as long as you’re comfy in it with the AC on. However, one problem that may occur is the overheating of the vehicle while the AC is on.

You’d want to know the reason for that bummer, wouldn’t you? Finding a solution would come to mind if you eventually discover the root of the problem. This is where the information contained in this guide comes in.
We’ll also be showing you how to avoid a repeat of such an occurrence with enough possible reasons explained. Never again, we say!


I. Car overheats when the AC is on: What are the symptoms?


Signs of car overheats when AC is on.
There are seven common signs that can tell you your car is overheating with the AC on.

1. Temperature gauge

Your car may be equipped with either a coolant temperature gauge or a warning temperature lamp. Monitor the former so it doesn’t go beyond 110 c. If so, then your car is overheating.

Both components will come on as a warning signal if there’s an unusual increase in engine coolant temperature. Check for coolant leaks regularly to ensure that either of the two components works as intended.

2. Car feeling physically hot

If your car is abnormally hot and you can smell rubber or plastic burning, it could mean that it has overheated. The smell could be a sign of plastics and gasket melting.

3. Ticking sounds from the engine compartment

If engine oil is utilized beyond the recommended period, it will stop being viscous. This will mean that it can no longer perform its function in the engine. Friction will start taking place due to the lumps that will be formed after such an occurrence. That could be the reason for the ticking sounds.

4. Engine shut down

This automatically happens as a precautionary measure in cars overheated—whether the AC is on or not. The car will only start when the temperature has gone down.

5. Strange odor

Your car’s engine is mainly metallic, but it has additional rubber seals and plastic components. Therefore, an overheated engine usually has a strange, ‘hot’ smell.

Furthermore, if you experience an unusual sweet smell, check if you have a leaking coolant situation. Look for coolant puddles on the ground after parking to be safe from leakages.

6. Speeding issues

In most cases, an engine problem like overheating will cause acceleration issues. Your car may also feel sluggish and fail to maintain the speed limit you prefer. Expanded pistons are mainly responsible for this predicament.

7. A cloud of steam

Steam emanating from under the hood is one of the most obvious signs of overheating. It may appear like smoke in some situations, but it is vapored. More often than not, steam results from evaporating coolant due to leakage.


II. Five reasons why your car overheats when AC is on


Now that you’ve noticed the problem of overheating, what could be the cause? Well, we’re about to explain the possibilities.

Five most common causes of car overheating when AC is on
Five most common causes of car overheating when AC is on.

1. AC compressor overload

It’s a fact that the compressor puts more load on the engine whenever the AC is on. Conduct a test by putting the AC on and observing the little boost in RPM (rotations/revolutions per minute).

Automobile makers try to ensure that car cooling systems won’t trigger any problems. However, issues start to come up when the compressor seizes, and the accessory belt stops it from turning. The vehicle will keep trying to turn the compressor leading to the overheating of the engine as a result of added pressure.

2. Problem with radiator

There can be blockages or interferences in the internal pipes of the radiator, which can negatively affect the flow of coolant and air in it, thereby causing overheating. It can be an accumulation of substances such as rust, dirt, and so on. Leakages may also be a factor.

3. Faulty fan

Your car can overheat when the AC is on, and you’re stuck in traffic or driving slowly. The problem is triggered when the cooling fan (including the cooling motor, fan clutch, or any other component that makes the cooling fan work) has a defect.

For example, the fan moves at diverse speeds depending on the load needed to cool the engine (your car may have two fans). The motor won’t receive adequate cooling if the fan isn’t performing as powerfully as it should—leading to overheating.

Another instance is when there are blockages or interferences in the radiator. Such a situation can lead to the restricted passage of coolant through to the vehicle’s engine, damaging the fan switch.

Apart from the above scenarios, a faulty fan relay can also be a possible factor. It’s obvious that there’s a need to perform maintenance checks on the cooling fan regularly.

4. Incompetent cooling system

Proceed to examine the other parts of the cooling system after you’ve checked the cooling fan and found nothing wrong with it…

The condenser converts cooling gas from its gaseous form to a liquefied state. It performs this primary role well as long as blockages don’t restrict the flow in the radiator. We discussed the radiator earlier. You can see how it’s an important part of the system in the prevention of overheating.

Back to the condenser—it heats up when the AC is working. This is why there’s a need for a cooling system to keep the condenser’s temperature at an optimal level. The cooling system needs to be performing as well as it should at all times.

Overheating can also be caused by a faulty water pump when the AC is on. A malfunctioning water pump will give rise to inadequate heat depletion.

5. Defective engine coolant sensor

The engine coolant sensor signals the control module to switch the cooling fans on, so this device may be the cause
of your overheated car. Why? It may not be signaling the control module correctly.

In case, after diagnosis, you still cannot find out the causes of this situation and things get even more complicated, you should scan for trouble codes related to your AC system using a trusted diagnostic scan tool. Hopefully, it will help you discover the root of the issue.


III. Quick solutions to fix the problem:


Implement the tips below depending on your discovery.

Five most common causes of car overheating when AC is on
Five most common causes of car overheating when AC is on.

1. Clean Your Radiator

Clean the radiator to get rid of blockages and interferences that will limit airflow and coolant passage. It should also be inspected for leakages with the aid of a radiator testing kit. Clamps and hoses should be substituted with new ones if needed.

2. Install an Air Pressure Gauge

The installation of an air pressure gauge is necessary to monitor the flow of air. It can be fixed at any of the radiator ends.

3. Flush the Coolant System

You should find out if this is what your car needs when it has overheated. Do this to make way for a new coolant mixture. You’d also be trying to get rid of corrosive substances, salts, dirt, rust, and so on.
Tip: Check the coolant system of your car regularly. Doing this will help you discover issues at their early stages before they become critical.

4. Change the Coolant Mixture Every 2 Years

You can do this at every 40,000 km covered. Ensure that you do so with a recommended product—in the right concentration. You should steer clear of tap water (use distilled water) because of the corrosive substances and salts that it may have. Doing these will prevent corrosion and rust in the radiator, water pump, and internal parts of the engine.

Important Notice: Use the right coolant.

5. Add Water to the Radiator

The radiator shouldn’t be dry, so ensure that water is added to it.
Tip: Always use distilled water instead of regular (tap) water to prevent unwanted substances like dirt from getting into the system.


IV. What to do if a car overheats with AC on in traffic?


This could be a real bummer. Aaargh! Still, try to keep calm and follow the tips below.

Step 1: Pull Over as Soon as Possible

This is the very first step that you should take. Ensure that the conditions are right before doing so. Remember, safety first.

Step 2: Turn Off the Car Air Conditioner

This should be done immediately, especially when you realize that there’s no chance to pull over. Confirm that it’s safe to set the vehicle in park or neutral when you have to wait for a stoplight. It’s a way to reduce the temperature of the engine a little.

Step 3: Open the Hood of Your Car

As stated earlier, safety first. Be sure that it’s OK to do this because of the temperature of the hood. Therefore, play safe by checking to see if steam is escaping from under it. If so, be patient for a while. Opening the hood will greatly reduce the temperature of the engine.

Step 4: Turn Off the Car Engine but Keep the Key in the Ignition and as it should be on Mode

Set the vehicle on park and put off the engine if you’re able to pull over successfully. The fan will continue running (in some car models) as long as you leave the key in on Mode. Substitute the fan with a new one if you discover that it isn’t on. This could also mean that it’s linked to the overheating problem.

Step 5: Check for Any Leakages

Once the engine has cooled down, proceed to check for leaks and/or call an expert for help. Patch up any leaks you find with radiator hose tape or by tightening a clamp. Fill up the radiator with coolant and water after. The expert you called should do a complete check to discover everything that went wrong with the engine.


V. Final Thoughts


Your car’s cooling system should be included in the periodic checks carried out on the vehicle. Ensure that you hire an expert to do so. The best decision to make would be to call a professional for help when the vehicle overheats, especially when you’re not sure about what to do. Abnormal heating can cause serious engine problems which may lead to internal damage. Be observant and take the appropriate steps.


Tim Miller, Author at Auto Trends Magazine

Charts supplied by Tim Miller. All rights reserved.

Author: Tim Miller
I’m Tim Miller, a mechanic and car blogger from Denver, Colorado. I’m the editor-in-chief of gmundercars.com - a blog about Automotive. My fan page is https://www.facebook.com/timautozik. I’ve had 10 years experience in car repair. Some of my review articles about car parts and tools can be found on my website.

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