How Many MPGs Are You Losing Running the Car AC?

Every time you switch on your car air conditioner, the motor has to work just a little bit harder. So, the question is, does using your car’s AC affect your MPG?

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Gas prices continue to rise and so getting the best fuel economy for your car is paramount. However, when you’re stuck in traffic on a hot summer day, few things can ease the stress better than a blast of cool air from your AC. But, every time you switch on your car air conditioner, the motor has to work just a little bit harder. So, the question is, does using your car’s AC affect your MPG?

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First, How Does Car AC Work?

A compressor, filled with refrigerant, is mounted on the engine. A pulley wheel, mounted on the front of the compressor, is engaged by the serpentine belt when the air conditioner switch is turned on. As the belt turns, the pulley spins and begins compressing the refrigerant. When working properly and charged adequately, the compressed refrigerant then works through a series of hoses and the radiator. The cooled, dehumidified air is then blown into car’s interior. Here is more on how car AC works. Ensuring that the car air conditioner is operating properly is one of many things that you can do to maintain your own car. Don’t forget to check your serpentine belt often for wear before it snaps.

Does Car AC Reduce MPGs?

Anytime an accessory (the radio, lights, etc.) that can be turned on or off is turned on, some energy is used. That extra energy is ultimately supplied by the combustion of gas. Because the car AC is powered by the car motor — when it turns on — that extra work on the motor requires extra fuel to maintain horsepower while the AC is turned on and operating. In addition to normal operations, when a cabin air filter is clogged, it can cause the AC to draw even more power or to work longer in order to cool the car. The additional work requires more gas to power the car.

So How Much Extra Gas Does Car AC Use?

The clear cut answer is, it depends. Each vehicle will differ. According to research done by Consumer Reports, the MPG varies between 1 and 4 MPG, depending on the vehicle. While this may seem insignificant, for an average-size sedan’s gas tank (with a 12 gallon tank), this may be as much as 12 to 48 miles per tank. With that being said, a few miles lost in fuel economy might be a small price to pay for a pleasant drive on a humid summer day.

LeRoy Demarest
I have worked for over a decade as an environmental scientist working on an advanced bioremdiation clean up project. For the past six years I have also worked as an adjunct instructor for several colleges, both F2F and online, teaching a number of science courses. Finally, I have been freelance writing for a variety of publications on the topics of: gardening, environment, construction, science, science education, academics and technical work.