Does Using AC in Your Car Actually Use Gas?

Staying cool while driving can be challenging, especially during summer. Many drivers have faced the unfortunate reality of their gas gauge getting too close to the big E. In these situations, you’ll do anything to conserve your remaining fuel, including turning off your AC. But does an AC in a car use gas?

This idea has been circulating since air conditioning became a standard feature in most vehicles. So is there any truth to it?

Let’s dive in and see!

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How Does the AC in Your Car Work?

A vehicle’s air conditioning system works on the same principle of any vapor compression refrigeration circuit. We wrote about this in more detail in our article about air conditioners as they all operate on the same principle. Refrigerators work on the same principle as well.

One of the most critical components in the system is refrigerant. In vehicles, this is typically a gas, R134A. This material can easily alter its physical properties based on pressure throughout the cooling process. 

The compressor, as its name implies, compresses the refrigerant. During this process, it becomes extremely hot and moves through a series of coils in the condenser. Outside air flows over the coils, removes the heat from the gas, and cools the gas into a liquid.

From there, the cooled liquid goes into the receiver-drier, absorbing moisture. The remnants move into the AC inline filter, which traps debris. The filtered liquid then goes through the expansion valve, turning it back into a gas before it travels into the evaporator. Its this phase change that takes energy and make the gas cold. This cold gas removes warm air as it flies through the evaporator.

From there, a blower connected to the system pushes the air against the evaporator to create cooled air. The cooled air goes out into the cab through the ventilation system. The final result is a cooler and much more comfortable vehicle.

The gas then returns to the compressor to repeat the cycle.

Does Using AC in Your Car Use More Gas?

The simple answer is Yes, running your AC uses more fuel. The simple fact is that the air conditioning compressor puts an extra load on the engine, and the energy needs to come from somewhere. Even in electric cars, the AC compressor uses a battery, it’s just an electric motor instead of belt driven compressor.

In 2017, Consumer Reports tackled this frequently-asked question. Their research indicated that running AC on an 85-degree day equated to a one to four miles per gallon decrease. The usage varies enormously from vehicle to vehicle and could be anywhere from 5% to 25% of a fuel economy decrease.

However, these results will vary by the model of your vehicle. Newer vehicles tend to be more efficient and experience less impact. Electric compressors tend to be more fuel efficient as well and help with electric and plug-in hybrid cooling. Additionally, the hotter your vehicle, the harder your air conditioner will work, so it’ll use more gas.

Lastly, the size of your vehicle and the space cooled makes a difference. A big diesel truck cooling just the cab will have much less of a fuel impact than a small sedan.

Pro Tip: Don’t get caught making a gas station faux pas. Find out Is It Illegal to Pump Gas With Your Car Running?

Is It Better to Open Car Windows Instead of Using AC to Save Gas?

An alternative to using your AC is to roll your windows down. However,opening windows can affect your vehicle’s aerodynamics and cause resistance. However, Consumer Reports also examined this belief. 

They found that a driver opening their windows at 65 mph had no measurable effect on their MPGs. So if your options are to open your windows or use AC, roll them down. However, the wind can be overwhelming if you drive on the interstate with your windows down.

This again is going to be very car dependent. A low profile sportscar will suffer significant drag from windows open compared to a truck. Wind resistance is also exponential with speed. At low speeds having your windows open wont make any difference in fuel economy while AC will. At high speeds however wind resistance increases and running your AC might make more sense.

Fuel-Saving Tips: How to Get the Most from Every Gallon

Depending on where you live, using air conditioning may be non-negotiable. As a result, you’ll want to take advantage of alternative ways to improve your fuel economy. Here are some tips to help you get the most out of every gallon.

Maintain Your Vehicle

Maintaining your vehicle helps ensure it lasts as long as possible and can also improve your fuel economy. Manufacturers typically include a recommended maintenance schedule in the owner’s manual for the vehicle. 

Follow the recommended maintenance schedule, especially for oil changes and replacing filters. Dirty filters can reduce airflow to critical components and cause fuel economy to tank.

Avoid Idling

You want to avoid idling as much as possible to maximize your miles per gallon. Why? You get zero miles per gallon when you let your vehicle sit with the engine running. While it may be minimal, it’s still wasting fuel. Many modern cars have automatic shut-off features to limit idling.

In addition to wasting fuel, idling is illegal in many areas. You could face fines and severe consequences if law enforcement catches you with your vehicle idling. The length of time varies by location, so know the rules and regulations where you live or are traveling.

Remove Unnecessary Weight

You want to do everything possible to make your engine’s job easier. The heavier your vehicle, the harder it will work, so you’ll use more fuel. The U.S. Department of Energy states that for every 100 pounds of weight, you reduce your fuel efficiency by approximately 1%.  This of course depends on vehicle size, this is for a standard sedan. A bus will see less impact from weight, but it will still make a difference.

Avoid unnecessarily carrying heavy items like tools, sports equipment, and other cargo. Stop hauling bags of clothes or boxes of books you plan to donate. By reducing your weight as much as possible, you’re doing your engine and wallet a favor.

Plan Your Route

It may require some advanced planning to make the gas in your car last, even if you turn off the AC. Stop-and-go traffic will kill your MPGs and is something you want to avoid if possible. It may mean adjusting when you leave to avoid congestion if it’s unavoidable.

Many GPS units will provide an option for the most fuel-efficient route. These typically factor in current traffic conditions, the shortest route, and the speed. Using technology lets you enjoy a smoother and more economical traveling experience.

Avoid Hard Accelerating

Another killer for your fuel economy is accelerating hard. When the light turns green, it’s not your chance to pretend you’re drag racing. In general, accelerating will cause your vehicle to work harder. Putting the pedal to the metal and seeing how fast you can go from zero to 60 won’t do you any favors.

When your RPMs go through the roof, your MPGs plummet. Do yourself a favor and accelerate firmly but not excessively. Just because your car can shoot off like a rocket doesn’t mean you have to.

Use Cruise Control

If you do a lot of highway driving, don’t be afraid to use cruise control. Maintaining a consistent speed can help you reduce any unnecessary accelerating or decelerating. Many newer vehicles come with adaptive cruise control, which uses radar sensors to adjust your speed according to traffic. Avoiding many minor throttle variations can help gas in your car go further over time like conserving AC.

However, it’s crucial to note that cruise control isn’t always the best option. It would be best if you only used it when in flat terrain. Using cruise control in hilly or mountainous areas can increase fuel consumption and cause damage to your transmission. Your vehicle will constantly change gears to maintain your designated speed.

Check Your Tire Pressure

When was the last time you checked your tire pressure? If it wasn’t recently, that’s one of the first things you should do after reading this article. Keeping your tires at the proper tire pressure can have a massive impact on your MPGs.

Experts indicate that properly inflating your tires can increase fuel efficiency by as much as 3%. In addition to increased MPGs, your tires will last longer. Check the PSI requirements on the sidewall of your tire and adjust the pressure accordingly.

By regularly checking your tire pressure, you’ll likely only have to make minor adjustments occasionally. However, don’t forget that cold temperatures can reduce the pressure in your tires. If you live in an area that experiences harsh winters, you may need to add some air once the temperatures drop.

Pro Tip: Make checking your tire pressure quick and easy with one of these Best RV Tire Pressure Monitoring Systems.

Combine Trips

Those quick trips to the store may not seem like a big deal, but they can destroy your MPGs. Instead of running to the store whenever you think of something you need, cranking the AC, and wasting gas in your car, create a shopping list. Grab the items on your list when making your next regular trip to the store for groceries or supplies.

Will this eliminate all wasteful trips? Absolutely not. However, it can significantly reduce them. Every little bit can help make every gallon of gas last as long as possible. 

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Stay Cool and Save Gas While Driving

It is possible to stay comfortable and save gas while you and your vehicle travel down the road. It may require planning and adjusting your driving habits, but it is possible. Unfortunately, we don’t have a magic wand to wave to make your vehicle more efficient.

For the best impact, focus on making many minor adjustments. Once you start to see the savings, it’ll become a game to see how much you can save. Your bank account will surely appreciate any savings at the pump.

Do you have any tips for staying cool on a long car trip? Tell us in the comments!

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