Air Conditioning In The Car.

Tilly2 | 15:09 Fri 18th Jul 2014 | Cars

45 Answers

Why does the car use up the petrol more quickly if you have the air conditioning on?

I have to keep putting petrol in. It's not lasting any time at all.

Mazda 2 Windows

I Have The Part Number But...

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Graham-W

You are asking the engine to drive an extra pump which works the air-con. This takes more energy and therefore uses more fuel.

woofgang

because its drawing power to run the compressor that makes the cold air.

Tilly2

Question Author

Oh, I see, Graham. Thank you. Nice simple answer there.

Tilly2

Question Author

Thank you too, woof.

gness

I think it's only at low speeds, Tilly....on modern cars it should be less noticeable at higher speeds....x

heathfield

Just like when you're driving with headlights on, when the alternator has to supply a higher amperage to compensate for the extra drain on the battery. This can reduce your MPG by around 1¼ to 1½%.

Graham-W

There's an ongoing argument about whether driving with a window wound down, causing extra turbulence, uses more fuel than running the air-con to cool the car.
I've never seen a definitive answer. Mythbusters did trials a couple of times without drawing a firm conclusion.

Tilly2

Question Author

Gness, my car never goes faster than 30 mph, if I can help it. That's why I have to keep refueling, I think.

I don't like going fast.

gness

Hi, Graham....the report I read....don't know if it's right....said windows down when stationary....closed and aircon on when moving.....though it has to be aircon for me, but I'm usually driving....fairly quickly.....☺

gness

Made me smile.....just looked at AA eco-driving advice....one recommendation is....Lose Weight.....I really had to think for a moment.☺

Graham-W

Gness. There's a couple of interesting graphs halfway down this page if you can be bothered. I agree with you if it's very hot. Air-con makes me more comfortable than window down ( at any speed).
http://www.vox.com/2014/5/24/5745364/why-rolling-down-your-cars-windows-is-more-fuel-efficient-than-using

Tilly2

Question Author

The part about ice vests is interesting. I could do with one of those on now.

gness

Thanks, Graham....did you notice one of their recommendations? Aircon off, windows closed and buy...for a few hundred dollars...an ice vest to stay cool whilst driving....and saving fuel......☺

Graham-W

LOL at "ice vest".

Tilly2

Question Author

Can you get ice vests in the UK, I wonder?

gness

Tilly, large cool bag with three holes cut in it?