I've not really noticed any great difference in fuel consumption for using the A/C in my last couple of cars, it doesn't seem to make any difference to fuel economy or performance in the E55, but then it's such a big tourquey engine that driving the compressor isn't going to make it break a sweat, I imagine most of the bigger engined petrols and diesels are the same, when I use a 1.6 Golf though it does use noticeably more fuel if you turn it on although performance isn't affected, so just wondering if other people notice it in their cars or not as I would be interested to know the sort of engine size/power output where the difference becomes un noticeable.