Does AC Use Gas in Your Car?

Article Summary:

Using the air conditioning in your car does indeed use gas and will lower your gas mileage, but not by a huge amount (roughly 3-10%). However, there are ways you can reduce the need to use your AC should the weather be hot and humid. There are also several ways to reduce fuel consumption in general if you want to save on fuel costs or fight climate change.

When it’s scorching hot out, your main prerogative is to get into your car as soon as possible and turn on the AC. However, once you flip that AC on and have a nice cool car, how much gas are you consuming? Is doing this beneficial for optimal gas mileage? These are important questions, especially when gas prices are high.

Your car does indeed consume gas when you use the air conditioning; however, it’s not consuming nearly as much gas as it uses to make the car move. The AC system is powered by your alternator, which is powered by your engine, the main gas-consuming element of your car. If you want to cut back on AC usage to save gas, you can drive (slowly) with the windows down or put a reflective covering on your windshield. If general gas consumption is a concern, there are multiple ways to reduce it while driving and maintaining your car. We’ll walk you through how your car’s air conditioning system works and ways to maximize efficiency.

Air conditioning in cars

In the 1940s, Packard became the first automaker to offer factory-installed general air conditioning. In 1953, General Motors, Chrysler, and Packard were the first companies to make modern air conditioning systems available in their cars. Before this time, people would use very primitive styles of cooling devices. The Knapp Limo-Sedan Fan was an example of this. It consisted of a small fan sitting atop the interior of the car. Unlike these first cooling devices, modern car air conditioning systems all work in a similar way.

AC uses electricity, which uses gas

Anything you use in your car that feeds off of electricity will use gas. The main supplier of electricity in your car is your alternator. An alternator functions by turning mechanical energy into electric energy.

How it works

Your engine powers a drive belt that is seated atop pulleys. The pulley spins the rotor shaft, which then spins magnets nearby the coil. The magnets create what’s known as alternator current (the other kind of AC). The alternator then channels this into its rectifier, which changes it from alternator current (AC) to direct current (DC). The direct current is distributed throughout the car. Typically, air conditioners use 3 kW of power.

Does driving without AC save on gas?

Driving your car without AC increases your fuel efficiency, but not by a huge amount. According to Transpoco, a leading company offering driving fleet management solutions, driving your car without air conditioning can increase your fuel efficiency by 4%.

The U.S. Department of Energy reports that using the AC can reduce your mileage by up to 25%. But with the efficiency of modern cars, you probably won’t lose that much unless you have an older car on the hottest, sunniest day.

Running the numbers, if you lose 10% efficiency and pay $50 for a tank of gas, it will cost you an extra $5 to run the AC.

How do AC systems work in cars?

Air conditioning systems use compression refrigeration systems. These systems involve the following elements.

AC compressor

The AC compressor takes the cold refrigerant and compresses it by raising the pressure, turning it into vapor. The vapor travels to the condenser.


The condenser then condenses the vapor into a liquid. When the vapor becomes condensed, it gives off excess heat in the process, resulting in the emission of hot air. The liquid then travels to the expansion valve.

Expansion valve

When the liquid refrigerant enters the expansion valve, it experiences a pressure drop. The liquid then travels to the receiver/dryer or accumulator.

Receiver/dryer or accumulator

The receiver dryer acts as another step to withdraw moisture from the refrigerant before it travels to the evaporator.


The refrigerant draws heat from the evaporator, resulting in the refrigerant becoming vaporized. The evaporator draws heat from the region that is to be cooled. The vaporized refrigerant returns to the compressor. The cycle then repeats.

A modern air conditioner works similarly to the modern compression refrigeration systems you find in most refrigerators.

Ways to reduce your AC use while driving in hot weather

If you want to save a few bucks on your next road trip, here are some ways to do it.

Drive with windows down

Does this really work? It’s debatable. If you drive slowly with the windows down, you can save on gas consumption by not turning on your AC. However, if you are driving on the highway, then it might actually be less fuel efficient and consume more gas. This is because the drag on your car with the windows open creates more friction against your car and thus uses more fuel to power it forward.

Use a sun reflector on your windshield

As long as you can still see well enough to drive, covering your window with a sun reflector or sunshade can cut down the amount of heat in your car. You can leave the reflector on while you’re driving as well as when you park to cut down on heat. In some cases, car wraps can act as a sun-reflecting element.

Use an electric fan

If you have an electric fan, particularly one that is powered by a solar battery, you can use that as a replacement for AC. Just like they used to use the Knapp Limo-Sedan Fan back in the day, you can use your own fan. The cool air might not be as cold as your AC, but it can do the trick.

Park in the shade

If possible, keep your car out of the full sun by parking in a shady spot or covered garage. You can also roll down the windows when you first get in to expel some of the built-up heat.

Pro Tip

You may be able to save additional money at the pump by using a rewards credit card that takes off a few cents a gallon. Check out our list of the best gas credit cards.

Other ways to be fuel efficient

As mentioned before, your AC does not use a tremendous amount of gas but does indeed use some gas. There are many other ways you can be fuel efficient while driving or maintaining your car. Here are some of the tried-and-true ways to save on gas.

Drive conservatively, brake slowly

Don’t rev your car up just to drive fast for the sake of it. If you keep your speed down to normal levels, you can save on fuel efficiency. Likewise, if you coast to brake rather than suddenly braking, this can also help reduce fuel consumption and improve overall fuel efficiency.

Change your air filter

If your cabin air filter is dirty, it may be making your AC work harder.

Drive in a higher gear if you’re driving fast; drive in a lower gear if you are driving slow

If you are driving fast, make sure that you are driving in a higher gear. Driving fast in a lower gear will put more pressure on the engine and decrease fuel efficiency. Likewise, if you are driving slow in a higher gear, this can also reduce fuel economy.

Pro Tip

Driving in non-rush-hour times can significantly increase your fuel efficiency. All of the stopping and starting you do in traffic is not good for efficiency. Likewise, it can cause you to constantly keep your car idling. You shouldn’t let your car idle for more than 30 seconds at any given time.

Tire Pressure

Make sure that your tires are properly inflated. Underinflated tires have a higher rolling resistance, which can reduce your fuel efficiency and consume more gas. Having properly inflated tires can help reduce this.

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How much gas does AC use?

Using air conditioning can reduce your fuel efficiency in the region of 3-10%. This is if you are actively using it in the typical summer heat.

Is gas needed for AC?

Yes, gas is typically used when you run the AC. However, if you don’t turn your car on, then you will be using the battery rather than the alternator.

Which AC setting saves gas?

Lower AC temperatures will consume more energy than more moderate temperatures. Instead of changing the settings frequently, set the AC to one temperature.

Does AC use gas or electricity?

In a gas car, you use your alternator to create electricity, which in turn uses gas. An electric car uses the battery to run the AC.

Key takeaways

  • Not using your car’s AC unit can conserve gas and increase fuel efficiency. However, it’s not a huge amount. How much fuel you are able to save and how much you can increase fuel efficiency is generally in the region of 3-10%.
  • If your car is older or you are driving in extreme heat, you could lose even more efficiency.
  • Driving slowly with the windows down, using a sunlight reflector or sunshade, and using an electric fan are ways you can cut down on your AC usage.
  • Traveling at normal speeds, driving conservatively, and making sure you are driving in the proper gear related to your speed can also help increase fuel efficiency.
  • Make sure your tires are properly inflated and that your cabin air filter is clean.
View Article Sources
  1. What does an alternator do? – Firestone
  2. 5 Tips for Saving Fuel – Transpoco Telematics
  3. The History of Air Conditioning in Cars – AAA
  4. Compression Refrigeration System – MIT
  5. Fuel Economy in Hot Weather – U.S. Department of Energy
  6. Attention drivers! Turn off your idling engines – Environmental Defense Fund.