Car Engine Overheats When AC Is On – Causes and Solutions

What comes to mind when the term “engine overheating” is mentioned? That sounds like bad news, of course! However, understanding the reasons for such an occurrence is the key to finding a solution to the problem.

If your car engine overheats when AC is on, it simply means there may be a problem with the HVAC system. Identifying the actual cause of the problem will minimize the energy you put in to overcome the challenge.

When your car’s air conditioner (AC) is turned on and you experience engine overheating, it indicates a car issue that can lead to an engine shutdown if not addressed. This bummer of a situation usually manifests with symptoms like increased temperature readings on your dashboard and possibly steam from the engine bay. Often, the culprits are the overloaded compressor, faulty cooling system parts or the damaged AC condenser.

For example, a malfunctioning condenser puts extra load on the engine, leading to overheating symptoms. This can result in significant engine and air conditioning system damage. The solution typically involves inspecting the cooling system and repairing or replacing the faulty condenser, compressor to restore optimal function.

So, why not take a moment to study some of the causes and symptoms of an engine overheating problem linked with the air conditioning system? The recommended solutions to the problem have also been captured in this article. So, ride on!

engine overheats when ac is on

Causes of Engine Overheats When AC is On

Virtually all components in your car should work in synergy with the engine, either directly or indirectly. The engine is the “chief burden bearer” of almost all operations in a vehicle, including the stress from the air conditioning system.

Meanwhile, if your car overheats when AC is on, one or more of the following issues are responsible for the problem like bad compressor, defective cooling fan, damaged cooling temperature sensor, clogged condenser or faulty coolant pump etc. Let’s go into depth.

AC compressor overload

The compressor is a significant part of your car’s air conditioning system. It is responsible for initiating the operation that finally releases the cold air you enjoy when the AC is on.

Typically, the AC compressor is in charge of compressing the refrigerant. It relies on the engine for power supply to carry out this operation. It is connected to the engine by a V-belt and a pulley.

When the compressor becomes faulty, it automatically puts more load on the vehicle’s engine shaft, which is a main culprit in a car overheating when AC is on.

Faulty cooling fan

The cooling fan is designed to expel the heat absorbed from a vehicle’s engine by pulling cold air and pushing out hot air through the radiator.

Therefore, if the cooling fan stops working, it will hinder this operation, thereby retaining the heat from the engine. When this occurs, an overheating problem is imminent.

Faulty coolant temp sensor

The coolant temp sensor is responsible for measuring the temperature of the cooling system’s antifreeze/coolant mix to constantly feed the ECM with information about the extent of heat generated by the engine.

A faulty coolant temperature sensor will provide conflicting information to the Electronic Control Module, resulting in overheating when you least expect it.

Blocked condenser fins

The condenser is built to receive the hot refrigerant from the compressor, remove the heat and transform it into a saturated liquid state, which is helpful for releasing cold air in the HVAC system.

However, the condenser fins that are designed to extract hot air from the AC are susceptible to being clogged up with dirt or debris. As a result, they cannot perform their function correctly when they become blocked. This can automatically trigger overheating. As a result, car ac cannot blow cold air.

Defective coolant pump

The coolant pump is responsible for maintaining engine temperature by pumping the coolant mixture around the vehicle’s engine compartment.

A weak or bad coolant pump will not be able to maintain the engine’s temperature as it ought to. This can further lead to an overheated engine.

Symptoms of Engine Overheats When AC is On

Several symptoms serve as quick alerts to inform a driver about overheating in a car. Some common signs associated with engine overheating when AC is on include the following.

Temperature gauge alert

Most cars are fitted with a warning temperature gauge, which helps to alert the driver about any abnormalities leading to unnecessary temperature rises. Ideally, your car AC temperature gauge shouldn’t exceed 110c. Otherwise, you most likely have an overheated engine.

Strong burning smell

A vehicle’s engine is built mainly with metals. However, the gasket and seals are made of rubber, which can melt quickly. So, if you suddenly perceive a burning smell in your car, it could be an overheated engine melting the gasket or any other plastic component.

Poor acceleration

Acceleration is a function of engine power. The more the power, the higher the capacity to accelerate. Therefore, if you suddenly notice a drop in acceleration or a sluggish movement while driving, the engine may suffer from a power loss of due to overheating.

Steam release

This is virtually the common sign most car owners understand. Once you notice a sudden release of steam (in the form of white smoke) from your car’s underhood, that’s an overheating issue you need to deal with.

Engine outage

A sudden engine shutdown is another sign of overheating. Again, this is more like a safety measure to prevent unexpected engine damage.

In other words, once a car’s engine starts overheating, it will affect the engine’s capacity to maintain its regular operation, which can trigger a sudden power outage. When this happens, the engine may not start until the car becomes cool again.

How to Fix Engine Overheating When AC is On

No matter what, do not underestimate the damage that overheating can cause to a car’s engine. However, before the problem degenerates into a more complicated issue, the following recommendations can help resolve engine overheating when your AC is on.

Top off coolant

Low coolant levels have various implications for a car’s air conditioning system’s operation. It may also be a culprit if you suddenly notice an overheated engine.

Therefore, ensure to check your coolant level regularly and refill when necessary. This can reduce overheating and rectify the problem of your car running hot when AC is on.

Remove excess freon

Too much freon in car AC will do more harm than good. Meanwhile, it can also contribute to engine overheating due to the stress it puts on the AC compressor to work on the excessive refrigerant.

So, if you notice excess freon in your car’s AC when dealing with an overheating problem, ensure to extract the excess refrigerant as soon as possible.

Unclog blocked condenser fins

An AC condenser fin comb can help eliminate debris or dirt blocking the condenser fins. If clogged condenser fins are responsible for the overheating, removing the elements blocking the component will automatically sanitize it again and resolve the overheating.

Replace faulty AC parts

Lastly, if the recommendations above seem unfruitful or you notice that one or more components in the air conditioning system are faulty or damaged, ensure to replace them immediately. This will go a long way to rectify the problem if your car overheats with AC on.


Should I turn on AC if car is overheating?

Do not turn on your car’s AC once you notice the engine overheating. As a matter of urgency, once you notice your vehicle’s temperature gauge rising, that’s the right time to turn off the AC if it was on initially.

The air conditioning system works with the power it outsources from the engine through the compressor. In other words, leaving the system on will put more pressure on the engine to work harder once you notice that your car is overheating with AC on.

Can a bad compressor cause car to overheat?

A bad AC compressor may not directly cause overheating. However, if you engage the component’s clutch and the compressor is not responding as expected, it will exert more stress on your car’s engine.

Meanwhile, once the engine suffers too much stress, it will surrender to the strain and overheat. So, ensure that your car’s compressor is always in good condition.

How do you know when AC compressor is bad?

The compressor is a major component of the air conditioning system; hence, a bad compressor will leave some apparent symptoms. Some signs include; clattering or rattling noise, reduced airflow, lack of cold air circulation, etc.

A bad or overheated AC compressor will reveal one or more of the symptoms above. Therefore, contact an expert auto technician to diagnose the problem and fix it immediately.

ac gets hot at idle

Can overcharged AC cause overheating?

An overcharged AC will cause overheating when the situation automatically affects the compressor, especially the clutch and pulley. This is because the compressor outsources power from the engine through these associate components.

Therefore, an overcharged AC will put more pressure on the compressor, which will most likely affect the clutch and pulley. When this occurs, it can trigger the engine to overheat due to too much strain.

Is AC bad for engine?

The air conditioning system is not a harmful component. However, its operation puts more burden on the engine than when it’s not running. This is because of the energy it derives from the engine through the compressor.

In other words, the AC can diminish your car’s engine power when constantly used. However, understanding how to use the AC effectively can be helpful. Meanwhile, observing a regular vehicle maintenance culture can remedy the drawbacks.


If you’re asking, “Does AC causes car to overheat?” Yes, it can, especially when there’s a problem with one or more components. However, do not panic if you suddenly discover that your car’s engine overheats when AC is on.

Being calm will be more helpful than moving randomly to find a solution. Therefore, maintain a calm state, turn off your car and carefully inspect to see what could be responsible for the problem.

Once you find out, go ahead and fix it immediately if you’re a DIYer. If you can’t, kindly contact a professional auto technician who can handle the fault perfectly.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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