Speaking as a former mechanic who still occasionally works on his own cars, this is the silliest, most drawn-out thread I’ve ever seen!
Asking if having the AC on uses more gas is like asking if towing a trailer uses more gas. Of course it does! Turning on the air conditioning engages a compressor which is driven by a belt off the car’s engine. It puts a greater load on the engine, i.e. it makes it use more fuel!
What is the big debate?!
Hail Ants, you are correct in saying that the car’s air conditioning system does put a greater load on the engine, which, of course, causes it to burn more fuel.
However, one would assume that in very hot weather, most people who choose not to operate the car’s air conditioner would also decide to open the windows.
It is commonly believed (and probably true) that driving at highway speeds with the windows open renders the car less aerodynamic, meaning it will also need more power to maintain its speed, meaning it will burn more fuel. I don’t have a cite to prove it, but I’d venture that auto manufacturers probably pay no attention whatsoever to the car’s aerodynamics with the window open.
I also think that one of the reasons there’s no simple answer is that it must also depend on the speed of the car. My guess is that 15 or 20 mph, windows up/down probably has little effect, meaning that the air conditioner would always reduce fuel economy at such a low speed. At high speeds, however, the answer is less clear.
Point taken.
I read Cecil’s column on it, and basically there are just too many variables to come up with any universal results.
Regardless of what car manufacturers may claim, at high speeds NO car (not even a Lamborghini) is especially aerodynamic. The majority of the engine’s power is being used just to push the air aside, windows up or down.
And, IMHO, air conditioning is there to make life a little more pleasant. If you’re such a penny-pinching miser that you don’t use it to save on gas, why don’t you just ride a freakin’ bicycle!