Last Updated: 11.04.2022

Turning on the air conditioning system drives out hot air and blows in cool air. This ensures your car is always comfortable, especially during long drives under the hot sun. When the AC is running, however, the compressor will force the engine to use a slightly higher percentage of fuel.

So, how much gas does AC use? That’s what we’re discussing in today’s post. By the end of this article, you will you’ll know if you need to control the use of air conditioning in your car.

What Powers the AC in Your Car?

How Does the Car AC Work?

car airconditioner interior picture

The air conditioning system is uniquely designed to remove hot air from the inside of your car and then blow cool air. This provides a cooler atmosphere inside the cabin. The AC can also pull mugginess from your windshield to improve visibility. The system is made up of several parts, including the compressor, condenser, expansion valve, evaporator, and/or dryer. The most important part, of course, is the compressor. 

How the AC Compressor Uses More Fuel

You can best understand how the AC uses fuel by knowing how it is powered. The operation of the air conditioning system in your car starts with the compressor.

The AC compressor is located in the engine block on the crank side of the car, and it runs off the drive belt. It allows the circulation of the refrigerant in the system and ensures the compression of the freon.

car airconditioner compressor image

The compressor assembly has a pulley on the outside that spins freely with the engine. Then, there is the armature in the middle that turns on the pump inside the compressor assembly. An electromagnetic clutch keeps the pulley and armature apart when the air conditioning is off. When the AC is turned on, the clutch engages the pulley, turning on the AC compressor.

The armature that keeps the compressor running uses the power supplied by the pulley to keep the system running. The additional force needed to keep the compressor running uses a little bit more fuel.

How the AC Electrical Components Use More Fuel

The AC system also depends on the alternator. This is an automotive generator that provides both the energy your car needs to operate as well as the electricity to recharge the car battery. It runs off the engine pulley.

The shaft speed of the alternator is determined by the pulley system. There are two types of pulley systems that can run the alternator: overdrive and underdrive.

car alternator with fan belt on engine room

An overdrive pulley spins the alternator faster than the crankshaft to ensure sufficient power production, but the alternator bearings may overheat. Also, an overdrive pulley puts more load on the motor, leading to more fuel consumption. The better alternative is an underdrive pulley. 

How Much Gas Does AC Use?

How much gas does AC use? Some claim that they get better mileage with the AC off than when it is on.

It is estimated that automotive air conditioning may increase fuel consumption by up to 10 percent. But, of course, there are other factors in play, such as when, where, and how you use the AC system. 

According to some reports, vehicles with a 1000cc engine may use approximately 0.6 liters of gas within 60 minutes when the car is parked. The fuel consumption may increase up to 1 to 1.2 liters for normal hatchback vehicles.

If your car AC, for example, uses 1 liter of fuel for every 100 kilometers, then the fuel consumption will be increasing gradually with increased distance. So, if you cover 14,000 kilometers in a year, your AC will use around 140 liters of gas.

Does Air Recirculation Help Lower Fuel Consumption?

setting the thermostat of a car aircon

Most modern vehicles have an air recirculation button that’s normally located on the dashboard by the cooling and heating controls. The button usually has a symbol of a curved arrow turning around on the inside of a car. When you press the button, the light will turn on.

Some people don’t know how to properly use this feature to boost fuel economy when the air conditioning system is on. So, let’s discuss how it works, when to use it, and when not to use it.

When you turn the air recirculation button off, it allows outside air to get into the cabin. But, when you turn it on, it simply recirculates the existing air inside the cabin. As long as the button stays on it will prevent outside air from getting into the cabin even if the blower is off.

When you turn on the AC, always be sure to turn on the air recirculation button. This will prevent the AC from having to cool a constant supply of warm air coming into the cabin from outside. This means the cabin will cool faster and also stay more comfortable. 

It also means the air conditioner will not have to continually work as hard. This will put less load on the engine and help to reduce fuel consumption. 

AC On Vs Windows Open – Which Is Better for Fuel Economy?

Aerodynamic Effects

We have seen from the very beginning of this article that the AC adds load on the engine, which leads to slightly higher fuel consumption. The AC compressor uses mechanical power, which is obtained from the pulley that runs off the engine.

You need to understand the aerodynamics of a vehicle when it moves to determine whether it is better to roll down the windows or turn on the AC. When your car is moving on the road, there is airflow opposing the movement of the car. This is referred to as drag, which increases with higher speed. A streamlined vehicle has a smaller coefficient of drag compared to a box-shaped one.

When you turn the air conditioning on the first thing you have to do is turn the windows up. This will significantly reduce the coefficient of drag and the drag force on your car. This helps reduce the load on the engine, especially when driving at higher speeds.

So, you can consider rolling down the windows and keeping the AC off to improve fuel economy when driving at lower speeds because the drag force will be less. But it isn’t advisable at higher speeds because you will only be increasing drag force and load on the engine even if the AC is off.

Acceleration Test at Different Speeds

There is an acceleration test we did to establish which option helps improve fuel economy. The test intervals were 30 to 40, 40 to 50, 50 to 60, and 60 to 70 miles per hour. We attempted to accelerate the car at different speed intervals when the windows were down with AC off and when windows were up with AC on.

The theory is that when you have AC on, you will be using more engine power. When you roll the windows down, you will be altering the aerodynamics of the vehicle, increasing the load on the engine because of the additional drag force.

From 30 to 40 miles per hour, the acceleration was about 7 percent slower with AC on than with windows down. From 40 to 50 miles per hour, the acceleration was around 4 percent slower with AC on than with windows down. Then from 50 to 60 miles per hour, the acceleration was around 3 percent slower when the AC was on than when windows were down. The acceleration, however, increased by around 0.5 percent when AC is on than when windows were down from 60 to 70 miles per hour.

According to these results, it is more fuel-efficient to have windows down with AC off at lower RPMs and windows up with AC on at higher RPMs.

Other Ways to Improve Fuel Economy

Here are a few things you can do to improve fuel economy when driving.

Start the Engine Before Turning On the AC

Whenever you turn on the car, make sure your air conditioning is not running. If the AC button is on when you start the car, the load on the engine will be much higher. When you turn on your car, the engine usually takes a few minutes to warm up. Also, the oil circulation takes a minute or two.

Don’t Immediately Turn the AC to Max Setting

One of the most common mistakes people make is to turn on the air conditioning to full blast as soon as they start the car. It is better to first lower the windows down and maybe even start driving for a few minutes to effectively let all the hot air out.

Then roll all the windows up to encapsulate the car. This will ensure that all the cool air coming out of the vents will be able to stay in the car. Turn the AC to the lowest temperature and the fan settings to the highest level. Then turn on the air recirculation button to keep the cool air recirculating inside the car.

Check Tire Pressure

Your air conditioning system keeps on increasing your fuel consumption. But did you know that your low tire pressure can also contribute to the already deteriorating fuel efficiency? Checking if you have the correct tire pressure is part of regular maintenance that you shouldn’t ignore.

Avoid Aggressive Driving After a Cold Start

Avoid using the gas pedal too much after a cold start with the AC on. Once you have started your car, the best way to save fuel is to keep a normal pace of driving and don’t go into too high revs.


How do I keep my car cool without air conditioning?

The first thing you can do is drive with windows down at lower speeds, although they don’t need to be completely down. Always park in the shade to avoid overheating your cabin. If you parked the car under the hot sun for a long time, open the doors before getting in to allow all the hot air to escape.

Do dirty AC filters increase fuel consumption?

The job of the cabin air filters is to remove or trap contaminants from the ventilated air. They help clean the air to make the cabin more comfortable. When these filters become dirty or get clogged, the AC blower motor suffers. It has to work extra hard, putting more strain on the engine. You may even notice a power reduction whenever you turn on the air conditioning system.

Related: Find out the signs of low freon in the car’s AC

So, Does AC Use More Fuel?

The AC compressor and the alternator run off the engine pulley. So, they add more load on the engine, increasing fuel consumption. The additional fuel your car uses when AC is on, however, also depends on how you use the air conditioning and air recirculation systems, the aerodynamics of the car, driving habits, and the condition of the car.