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With the heat upon us (36 degrees seen here today!!!), we'll no doubt be using our aircon/climate a tad more.......

but what REAL difference does it make the the MPG??

How costly is it to run?
 

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I was thinking the exact same question today! I've done my usual 100 mile weekend journey today and normally I get 32mpg crusing about 80mph along the motorway, today with the air con on the second notch (I'm not posh enough to have climate) it was down to 30.2, but that could be to do with anything. It was certainly lovely though in my car, much better than having your window down when yoru doing 80 like I saw a few older cars having to do!

I was told once, but don't know how true this is, that it's more economical to have air con running on the motorway than it is to have the windows down because of the drag you create by having them down, if anyone wants to explain why this wouldn't be true or why it might be true, then please, feel free!!![*-)]
 

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Whatever you normally spend to travel 100 miles in your mkiv will only get you aprox 92 miles with the A/Con on, it does vary depending on use and conditions 'sitting in traffic' etc but for a guide thats as close as you will get.

However in a mkv, its a more efficient system and you would expect to see 96 miles instead of the 100 [;)]
 

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I covered 120 miles yesterday with temp at 29-30C most of the time and got 52mpg for speeds between 50 and 80mph. On a cooler day(18-20 C) I've got 55mpg for similar journey/speeds. Fuel econ on both my old 1.8Ts hardly varied though.
 

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Ive heard of that wind drag thing before as well. I suppose cars are designed in wind tunnels are as as smooth as they can be, when you have a window or sunroof open it disturbs the flow of air = more drag + more fuel used. I only notice 1 or 2 loss in mpg the same as you in my MK4 1.8T. in my derv MK5 i just leave it on all the time (i dont pay for the fuel) and it gets 48 to 56 mpg (mostly motorway 60 / 80 mph)

Richy...
 

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Yeah i remember a while back now there was a thing on top gear about how to increase MPG , and having the windows opened was one of the ways it can suffer.
 

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With my climate on, it does'nt seem to make any difference to the MPG, even over this weekend where its been going overtime.
 

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I leave mine on all the time except when driving through a stinky polluted atmosphere ie behind a truck or similar. The MPG does suffer, it drops from 53mpg to 51. Such terrible economy.[:D]
 

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TBH if you can afford a car with working air con / climate you can probably afford to run it.  I leave mine on most of the time, however in winter I will probably turn it off. Luckily I have a MKV so the systems still runs a tiny bit when it is turned off, this means I don't have to remember to turn it on every so often to keep the seals fom perishing.
 

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didnt realy notice mind change that much  and was on motorway so prob had better mpg coz of that  but around town it drops just a little bit
 

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I leave mine on all the time except when driving through a stinky polluted atmosphere ie behind a truck or similar. The MPG does suffer, it drops from 53mpg to 51. Such terrible economy.[:D]
When in traffic you should press the recirculate button as well as your aircon- that makes sure you dont suck in any stinky fumes and simply uses the air already in the car.
 

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Never noticed any difference on the V5. We ended up just leaving it on Auto all the time. I do the same with our A4 although we're only getting around 42-44 mpg - it's a PD130 Sport/
 

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snip........I don't have to remember to turn it on every so often to keep the seals fom perishing.
Is it worth saving fractions on mpg only to have to spend ?hundreds when the system fails......?

I keep my a/c on in the Golf all the time and the climate in the BMW is on Auto all the time.
 

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snip........I don't have to remember to turn it on every so often to keep the seals fom perishing.
Is it worth saving fractions on mpg only to have to spend ?hundreds when the system fails......?

I keep my a/c on in the Golf all the time and the climate in the BMW is on Auto all the time.
Well for MKV owners we don't worry. I guess the MKIV people need to keep running it.
 

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I've never noticed much difference, on the odd occasion when I've used the aircon.

Certainly not in my old Golf 1.8T - haven't really used it much in the A3 1.8T yet.

I wonder: maybe in town, A/C has a big effect on fuel consumption, because the engine is often idling (and therefore the A/C is a high load). Whereas on motorways, the engine is always running at a good few revs, so the A/C isn't such a large additional load..?

Just a theory. I've never noticed a massive fuel consumption change, anyway [:)]
 
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