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Is it true that we use more fuel when using the air conditioner? If so, how much?

Tests by the AA have shown that using your air conditioning can increase fuel consumption by about 9%. But air conditioning is very useful in keeping drivers comfortable and reducing fatigue, especially on long trips. Its also better than driving with your windows down, which increases drag so also increases fuel consumption. Our advice is to use air con sensibly, you may not need it for short trips or during mild weather but you should use it on longer journeys or if it is hot. Its also very effective at demisting in cold weather, which is another safety benefit. The air con system also needs to be used at least once week to keep it in good working condition.

If I don't have the a/c on I find the windows fog up almost instantly. So I leave it on pretty much all the time...

Thanks, that's useful info re using it once a week.

Thank you, that is very helpful

Never heard the once per week bit before, here i thought I was doing myself a benefit only using the a/c when I was actually uncomfortable!

I found that reply most interesting.