The Truth about your Automotive A/C System

How does your A/C System affect gas mileage?

The Truth about your Automotive A/C System


It's a beautiful summer day, and you have a decision to make: do you roll down the windows and let the breeze run through your hair, or do you keep the windows shut tightly and run your A/C system to cool down your car? Can you do both?People often ask and wonder if they can run their A/C system while they have the windows down in order to stay comfortable in the car cabin.

When your A/C Unit is on, the compressor is running continously to push air into the car cabin and control the temperature by adding heat to the air.

There are vehicles on the road that have temperature control settings as well as vehicles that do not. With vehicle that do, the compressor will work less or turn off when the desire temperature is reached. Vehicles that don't have temperature settings have to manipulate the fan or adjust the cooling settings through the settings available on the dashboard. If the air in the cabin cannot be brought down with normal effort, the compressor will work harder and continuously.

When hot air flows over the cooling coil, it raises the temperature of the freon that returns to the compressor. This raises the overall pressure in the system that the compressor works against, which makes the engine work harder to keep the compressor turning.

What about gas mileage, will doing both affect fuel economy negatively? Running your A/C unit does lower gas mileage, as does driving with the windows down. So it's safe to say that doing both at the same time, is going to burn through your gas a little faster and you'll get fewer miles to the gallon, which slowly adds up.

A study from the Society of Automotive Engineers (SAE) revealed that driving with the windows up and the Air Conditioning on is more fuel efficient for driving. Driving with the windows down has a significant negative effect on gas mileage, far more than it does to operate your A/C System. Read the full article here.

The well known crew from the show of Mythbusters attempted to verify or debunk this theory by getting two identical SUVs, and directly compare fuel economy between using A/C and driving with the windows down. In their study, Adam's SUV drove 15 miles further with the windows down than Jaime's SUV with the A/C running. Learn about the whole experiment on the official Discovery Mythbuster's Website.

If your A/C isn't producing cold air or not pushing air at all, you should have your A/C System inspected by an ASE Certified Technician as soon as you can. Air Conditioning Repairs can be expensive and time consuming. Have your A/C System inspected annually for the spring/summer season to guarantee peak performance.