Do you notice A/C using up more fuel in your car?

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cant say ive noticed any differance either!

do you guys turn your aircon off if you open your windows or sunroof? i tend to and then forget its off! until i cant breath! :)
 
So if at 100% it adds 12-25% then at say 10% or 20% load/duty it's only making an overall impact of 1.2% to 5%.

Judging by the rise in temperature of both the condenser and engine cooling system, it's running a lot more than 10-20% duty cycle.

I can see a 10-20 degree C rise in combustion temperature at idle as a result of engaging A/c, which is a direct result of more fuel being burned.
 
cant say ive noticed any differance either!

do you guys turn your aircon off if you open your windows or sunroof? i tend to and then forget its off! until i cant breath! :)

Yes I turn mine off when anyone opens a window why try to cool down the planet. The air con is good in a MB but it isn't good enough to reverse global warming.:thumb::D
 
I can see a 10-20 degree C rise in combustion temperature at idle as a result of engaging A/c, which is a direct result of more fuel being burned.

But what does that actually mean in terms of energy?
 
At idle that's about 15% more fuel being used.

Which presumably doesn't translate to anything like 15% when cruising?

Which brings things back into the 1.2% to 5% extrapolation above?
 
For my car:

Engine load aircon off at idle: 21%

Engine load aircon on at idle: 26%

So idling with aircon on is using nearly 25% more fuel than off!

However, at speed it'll be negligable.
 
Anything which helps to stem the tide of global warming is to be welcomed so in the summer we should all run a/c at full bore, cold as possible and with windows/roof down. ;)
 
A/C said to hit mpg by 8%
Only noticed it on my 99 Mondeo 2.0 auto when it would drop from 16mpg to 12mpg
Although in 20 yrs virtually nothing has worsened or improved my mpg
 
Surely if you have a car with air con, then use it comfort is the prime reason for having it isn't it :bannana:
 
Driving with windows open uses more fuel than the aircon due to increased drag.

Either leave the aircon on all the time or buy a more economical car if fuel consumption is a concern.
 
I have noticed significant difference in performance and fuel economy on most of my previous cars but not with the mercedes. Now i can smuggle peanuts whenever i want and give a fiddlers :)
 
Indeed, you can't beat the laws of physics.
Running the air con pump obviously uses more fuel.

First Law of Thermodynamics ...
"You don't get 'owt for nowt"

The effect on your fuel consumption is all relative.
Big powerful engine with small air con pump or low duty-cycle won't make that much difference to your fuel efficiency.
With a lower-power engine, the relative effect will be more noticeable.

It also works the other way round.
Some US West-Coast vehicles are fitted with pretty-awesome air con.
When you switch that on, the effect can be very-significant.
But, again ...
You don't get 'owt for nowt.

It used to be one of the jokes of my American car days.
Some of the monster Cadillacs, Chevs and Oldsmobiles of the 1970s (typically 454 or 500 cubic inch displacement V8s) were hopelessly fuel-inefficient ... They weighed about 3 tons and were not helped by the addition of all sorts of wacky emission-control gear.
Typical consumption could be 8 to the gallon.
The joke was that you could drag this down another couple of mpg by switching in the mega air-con pump on a hot day.
Those were the days.

The air-con on modern MBs is rather more refined (certainly in UK cars).
On the two E300TDs and on the E430, I have not really seen it make that much difference.
It must do, but it's not all that noticeable.

It was more noticeable on the W124 230TE that I ran for a while.
Fuel consumption on that car was pretty poor, and the air con did appear to drag it down even more.

However ... You don't a large E-Class for fuel-economy and the purpose of air-con is comfort rather than cheap motoring.
 
Not as simple as that - depends on the speed.

I did wonder this.

At what stage or speed etc. does aircon become more economical than drag caused by open windows.

I couldn't be less interested in physics so I have no idea - but for some reason, I wasn't convinced one or the other was more or less economical...

I don't care because I love the sound with the windows down but still...
 
I did wonder this.

At what stage or speed etc. does aircon become more economical than drag caused by open windows.

..

I lost 5-6mph with the roof down...mind I was doing 158mph...roof up was getting 164mph ish.....A/c was off.

single digit mpg too....

:D
 
At what stage or speed etc. does aircon become more economical than drag caused by open windows.
It will vary from vehicle to vehicle depending on the aerodynamics and power consumption of the aircon, also how wide open the windows are. I think the normal quote is based on them being fully down, which isn't particularly realistic for most people!
 
Not as simple as that - depends on the speed.

Of course it does depend on the speed. I was giving a general assumption of the typical car journey, including A, B and possibly Motorways. The open window method also depends on the air temperature which I omitted to mention.
 
Over here the day temps have been in the mid 30's for around 10 weeks now with the occasional chilly 26, even night time rarely goes below 22, Now of course mine is an old fashioned A.C. just push the EC button and the light goes out and the AC is on. But driving an old E300 OM606 diesel up some steep hills around here you do benefit from prodding the same button lighting it up and turning it off to get up them. Just turning it on when idling makes the engine die a little. But it is pleasantly cool as a cucumber inside.
 

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