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jasperhappy 
Groupie
Joined: 05-May-2004
Location: United Kingdom
Status: Offline
Points: 74
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 Topic: air con and mpg
Posted: 18-August-2004 at 09:59 |
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hello .......is it true that having the air con switched on affects the fuel consumption......if this is true can one of you boffins explain why.....also by what amount does it affect it.........thanks......don,t you think that apart from rennies and ventolin inhalers that aircon is one of thye greatest inventions lol ....jasper
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[img]http://jasphotos[/img/
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e34m5
Really Senior Member II
Joined: 26-June-2003
Location: Near Rugby, Warwickshire
Status: Offline
Points: 1344
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Posted: 18-August-2004 at 10:08 |
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Yes it will reduce your MPG, this is because the compressor is using power from the engine which would normally be used to power the car so the engine has to work harder ? I believe most air con compressors use around 5-10Bhp (But i could be wrong ?) I have also heard that driving with your window open at 60Mph would cause the same drop in MPG due to the additional drag caused by disrupting the airflow around the car. Driving with the Aircon turned on in my car reduces the fuel economy (as indicated on the OBC) by around 0.5-1.0mpg ...
Miles
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dave 328
Really Senior Member II
Joined: 21-October-2003
Location: United Kingdom
Status: Offline
Points: 835
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Posted: 18-August-2004 at 10:09 |
Yes it does.
Your mpg on average will drop by about 2-5mpg. So it drops economy by about 5-10%.
The reason is because the engine has to drive the compressor/pump which does put a load on the engine using more fuel - similar to winter driving with heater, lights etc on, this makes the alternator work harder, albeit not to the extent of air-con.
If you drive on a light throttle then switch the air-con on you will feel the load put on the engine - feels like you have very lightly applied the brakes.
Driving with the windows open will also create a drop in mpg - because of drag.
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328 Coupe Sport, Digital climate, full leather, OBD computer, De-restricted with M50 manifold, big bore throttle, chippeduk remap, custom cold cone intake and X-brace
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e34m5
Really Senior Member II
Joined: 26-June-2003
Location: Near Rugby, Warwickshire
Status: Offline
Points: 1344
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Posted: 18-August-2004 at 10:11 |
Snap 
Miles
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dave 328
Really Senior Member II
Joined: 21-October-2003
Location: United Kingdom
Status: Offline
Points: 835
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Posted: 18-August-2004 at 10:14 |
 
I Hired a 1.0 Micra with air-con in Lanzarote and had to turn it off when overtaking as it zapped the power - it was like a nitro button!
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328 Coupe Sport, Digital climate, full leather, OBD computer, De-restricted with M50 manifold, big bore throttle, chippeduk remap, custom cold cone intake and X-brace
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BMWE34sport
Really Senior Member I
Joined: 30-April-2004
Location: Hertfordshire
Status: Offline
Points: 353
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Posted: 18-August-2004 at 10:19 |
friend of mine was driving one of those small weird tall vauxhall thinghs the other week ..can't remember what it was called ...he said he had to turn the air con off to get up a steep hill cos it lost so much power 
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1991 525 Sport
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jasperhappy
Groupie
Joined: 05-May-2004
Location: United Kingdom
Status: Offline
Points: 74
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Posted: 18-August-2004 at 19:05 |
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thanks a lot for your help everyone........think i'll just use it when i'm going downhill ...jasper
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[img]http://jasphotos[/img/
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studyolic
Really Senior Member I
Joined: 09-July-2004
Location: Inchture, Dundee, Scotland.
Status: Offline
Points: 427
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Posted: 18-August-2004 at 19:52 |
It also depends on how many ponies you have under the bonnet. The more you have, the less you'll miss a couple of them, and if you have an awful lot of ponies, your fuel economy is so poor you probably won't notice the difference whether the A/C is on or off.
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Retset
Groupie
Joined: 12-August-2004
Location: United Kingdom
Status: Offline
Points: 53
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Posted: 18-August-2004 at 22:14 |
That's true - I can't tell the difference 
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525IX
Groupie
Joined: 07-March-2004
Status: Offline
Points: 66
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Posted: 18-August-2004 at 23:05 |
Turn on your lights, HRW,blower and you will use more juice!
How much more fuel you use will depend on the outside temperature, the hotter it is the harder it will work. The Toyota Tercell that was my company runabout when I was in Dubai would lose 2-3 Kmh at 165 Kmh, so if the Vauxhall Tallthingy wont go up a hill with the ac on then there is something very wrong. Many European cars are fitted with what is called a variable displacement compressor, which means that the compressor will match its output to the heatload IE if it aint cold the compressor will pump less refrigerant, which takes less power. Sadly BMW are still in the dark ages and are fitted with the older design compressors that cycle on and off
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air con and mpg
