So its been stupid hot in Wisconsin for the past 4/5 days, so my AC has been blasting.

I usually get 29/30 mpg with my 250awd when using AC now and then, or just for a bit to cool the car down compared to the last week that it has been at 60* for 100% of my drive.

I'm averaging like 25 mpgs this week - same driving habits and whatnot... sort of shocked that it knocks that much off. Anyone else notice how much it affects theirs?

 

Interesting, I see the effect on mine but not that bad. On the highway, it doesn't actually seem to make a change. But living in California, i always have the A/C on and i can tell, when i do more city driving, my MPG is worse in the city with the A/C on. I just turn it off and roll down the windows when i'm driving in the city. Otherwise, i think im seeing something like 2-3 mpg less in the city.

 

that is perfectly normal. AC saps anywhere between 2-5 mpg

 

i drive between northern and southern california all the time. whether ac is on or off i get 27-28 mpg according to computer. in fact the 28 was when i had the ac on the entire time.

 

I was pretty shocked it hit that hard, its almost like a 15% drop.

I did see on Yahoo the other day that:
MPG w/ AC > MPG windows open .... AC on newer cars is more efficient than windows open