Air Condition vs Windows Down

[new92]

Do you got more mpg with.....

a) Air condition on and windows up
b) Air condition off and windows up
or
c) Air condition off and windows down

I have seen a couple of articles that question that b or c is the better of the two. But I dont have an exact answer.

[AeroModder]

B would be the best, but I'm wondering about the comparison between A and C, since I removed the air conditioning, and I'd like to know if rolling down the windows is worse than having the AC on.

[hyperme]

I would think in all situations, b) would definitely be the best. Whether a) or c) is better has been an ongoing debate and depends an the circumstances, the primary one of which I believe is speed. This assumes your a/c is working properly.

[brucey]

I've seen a lot of tests, and people always test with all windows down versus A/C

I usually run one window open (or just cracked even) and no A/C and feel this is the best way, up to at least 70 mph, which I never go that fast anyway.

[Frank]

Factory aero design works best with windows UP. If you feel guilty about running the A/C slow down 5 mph and you'll get even better mileage.

[ChopsQube]

It has been proven by several organizations, including MythBusters and myself that driving with the a/c on and windows up is better than driving with the a/c off and windows down. It's a simple comparison that you can easily conduct yourself. There's really no reason to see what others have to say.

Although, I don't think that "B" should even be an option as the answer is clear. No a/c means less drag on the engine, and all windows closed means less air drag which in turn means less drag on the engine.

However, running with the a/c off and the windows up in the summer time in the more tropic areas of the world when you have a car with a perfectly functioning a/c system, I'm willing to sacrifice a couple MPG to be comfortable. The a/c in my first vehicle died six months after I bought it and I couldn't afford to get it fixed. I never want to repeat that ever again.

[ShadeTreeMech]

Using the a/c intermitently fetched me some decent mpg figures. But whenever it is feasible, I crack open a window (or the sunroof) and use the vents.

I'm with ChopsQube, a couple mpg loss is worth it to not sweat like a horse. But there is a lot to be said about finding a happy medium between windows down and ac cranked full blast. In my van I'll turn off the a/c as much as possible or turn the blower to the lowest setting; makes me wish for a thermostat inline with the a/c switch.

Be careful mentioning mythbusters around here; you'll be told how unscientific they tend to be.

[Piwoslaw]

I think the answer depends on:

• The make and model of the car,
• How efficient its A/C is,
• How many and how much the windows are opened.

Check out these two threads:
Windows down on VW Golf = 2.5% FE reduction
Tested: what's the resolution of coastdown testing? Can it register an open window?

[new92]

thanks for everyones feedback. I was pretty sure b was the correct one, but wasn't sure on a and c.

BTW: Love the forum

[cfg83]

Piwoslaw -

Originally Posted by Piwoslaw

I think the answer depends on:

• The make and model of the car,
• How efficient its A/C is,
• How many and how much the windows are opened.

...

These are good points. For instance, if you have a V8, the A/C is a lower percentage of your engine load, so it's a more reasonable tradeoff. On my 1.9 liter 4-banger, it has a much bigger effect and I can really feel the HP drain when I try to accelerate. I can see A/C killing my MPG on the ScanGauge because the engine load is much greater.

And yes, b is best, but it can be a hard thing to do in August. I usually do what brucey does, window open or cracked. When I hit bad traffic and have to slow down, I lower all the windows a lot until things speed up again.

CarloSW2