Effect of running A/C on mileage
 

The weather is warming up here in TX - am running A/C most of the time now. My mileage seems to be dropping a little, but it bounces around between 26 and 31 anyway.

For those of you who keep track of mpg - how much does running the A/C affect your mileage numbers?

Thanks,

I haven't really seen any difference. I'm convinced that the increased aerodynamic drag of opening the windows and sunroof will increase fuel consumption more that the AC will.

The AC on my 220D has never worked, but I'm hoping to do a Sanden conversion at some point over the summer and I'll let you know! I've been tracking my mileage on it with Fuelly for nearly 3 years now.

I've read studies that this is true.

Winter diesel does worse on mileage because of the blend, so when you switch to better fuel, but using the AC, for me its generally a wash.

My girlfriend seems to pick up 1-2 mpg in the 190D in the spring and fall when the windows are up and the A/C is off, but not necessarily on winter blend fuel.

Windows down uses a lot more fuel than AC on newer cars. On our older cars I'd say it's mostly as wash below 50 mph.

-J

In my truck I get 26-28 with the window down. I get 30-32 with the windows up. But the AC is busted, so there's no way I'm cooking :P

I run the center vents wide open with ac off for cooling. I get around 40... haven't needed ac yet with the car...

Max is right. When I was with the EPA I was a team member at the TRC track in Ohio (now owned by Honda) and we ran instrumented cars on a defined driving schedule on the track. One of the things we tested was the AC on vs. windows down thing. There was definitely a point where the AC on beat windows down every time. That point varied with the drag (air resistance) of the body in question. Most pickups found their AC "happy place" around 45 MPH, most cars about 35 or so. There are a ton of variables including tire type and so on. Before anyone asks, we only ran in very limited ambient conditions and we waited frequently for the wind speed to drop, the temp to warm up, etc. One of the biggest issues with on-road testing is attaining repeatable conditions.

I can easily bore you with WAY more than you ever wanted to know about this stuff!

Dan

Effect of running A/C on mileage
 

2014 Nissan Versa. 1.5 mpg drop with AC. Windows closed either way.

The Benz? No idea as the AC pump is located on the work bench...

1-2 mpg on modem cars with A/C. The converse is not true, you get it for free or almost free on heat. Would expect to be the same for older cars. This is obvious as you do not get something for nothing. I will take the loss any time in SoCal. :)

The biggest woe with ac is noticed with performance cars. The ac will limit rev freedom...
Most have an ac cutout switch when fully accelerated, but if full pedal travel isn't made, the drag from the pump is serious.

:confused::confused: I think the OP is asking for mileage impact.

603 Motor A/C = 2 to 3 MPG off Non A/C MPG
 

I find that my 603 SDL drops 2 to 3 MPG when the A/C is on.

Just comparing mileage on years of monthly 800 to 1,500 mile trips around the Southwest during winter vs. summer.

I also hear that the turbo does not compress hot air i.e. @ 100*f + as well as in cooler conditions i.e. 65*f. So along with compressor drag that may factor in.

There also seems to be a noticeable power performance drag with the A/C on. When in AZ during the summer at 110*f I occasionally click off the A/C when merging onto the freeway...very noticeable power increase with out the A/C.

On a '96 Ford Contour 4 cyl, about 2 mpg loss on highway. I do not know on my '81 MB 240D. I do think the older York and GM compressors have a bigger loss. The OP did not state which MB that had a 2 mpg loss. I do not know or can comment on AC vs windows down. I would think AC beats windows down (2-55 AC). I never did a MPG in my Bricklin with a York compressor. The HP drop was noticeable, as I remember. I did notice an HP drop on the Contour, but not as much.

Thanks to all who replied. I was asking about mileage, and my '97 in particular - noticed a mileage drop from 30 to 28 or so right around the time I started using A/C. I've only been tracking my mileage for a year and don't really have complete data. But a drop of 2 mpg sounds reasonable, especially with a fair amount of city and stop and go I sometimes do. I noticed today that the A/C on the right side blows colder than the driver's side, so I need to start reading up on the duovalve repair.

My old '85 on the other hand - when the A/C worked - returned a steady 22-23 mpg on 100% biodiesel whether I ran the A/C or not, no matter if I drove mainly city or highway miles.