Air conditioning and fuel efficiency

What fuel savings (percentage) can you expect if you didn’t run the A/C at all versus running most hot summer days? Can you expect more fuel efficiency if you ran it at say half coolness setting versus the coldest setting or does it matter at all?

On old style inefficient air conditioners, the mileage penalty was about 5%, comared to driving without and the windows CLOSED. Opening the windows eats into those savings, however. Today’s units are far more efficient.

When you use the A/C, select the highest temperature you can put up with and put the fan on medium.

The small penalty in fuel mileage these days is a small price to pay for comfort. A collegue of mine who drives a lot in hot weather says if he had to choose between A/C and WHEELS on a car, he’d take A/C!!

Bad advice. The higher you set the temperature, the lower your mileage. The AC compressor remains on regardless of the temperature setting. (It may cycle off more if you set the fan to a lower speed.) The climate control on this car works by adding in more heat from the heater core if you select a warmer temperature. That just makes the AC have to work even harder. For maximum economy, select the lowest temperature, lowest fan speed, and set it to recycle instead of fresh air. At the end of the year, you will have burned one gallon less than if you have left it where you were comfortable.

You can expect only a few percent saving in most cars. If you are considering opening the windows on the highway and leaving the A/C off, you will only be less comfortable and lower mileage.

Short answer: it does not matter.


Running the air drops gas mileage around 1 mpg on our 27 mpg car with a fuel mileage calculator.

Some say that increased aerodynamic resistance due to open windows and air off vs windows closed and air on makes no difference but I have not verified this.

Half cool should be give better gas mileage than full cool with the windows closed in both instances but that is from reasoning, not observation.

I live in AZ, and today for example, it is 107 degrees outside! You can bet I’m running my AC all the time. I do see a difference in mpg in the summer months, but it is a really small difference, I don’t think its near 1 mpg. Unfortunetly, even it was, I would still have to do it. Is the small decrease really worth being miserable? My advise, enjoy the AC!!!

Yes, A/C has a mileage penalty…But most people have such poor driving habits it’s almost impossible for them to get any WORSE mileage than they are already getting, so why worry about it??

Air conditioning does have a mpg penalty, but it is slight, and many people, myself included, will take the comfort over the slight decrease in fuel economy. In my car, I may get 300 miles out of a tank of gas running the a/c and 320 if I don’t run the a/c. Most people won’t see that much of a difference. The reason I do is because I drive a 1990 Buick Skylark with a heavy, all iron engine with a factory rated 90 horsepower. I have to drive it a little harder to get on the Interstate with the a/c on than with it off, but it still has a full R12 charge maintenance free in the six years I’ve had the car, and blows cold enough to hang meat in that car, so I enjoy it rather than suffer, and live with the mpg decrease.