I would like to agree that our MB should be affected less by having the air on than our Honda, but this doesn't seem to be the case. We have an 89 Prelude and an 89 190E 2.6. On the Honda you can hardly tell by performance and mileage that the AC has been on, but on the 190 it's very noticable. In fairness, I should say that the AC has always been very noticable on my BMW as well.