micalee Posted July 1, 2009 Report Share Posted July 1, 2009 As the title says, does climate control/air con use as much fuel as we may believe? Link to comment Share on other sites More sharing options...
Drewcam Posted July 1, 2009 Report Share Posted July 1, 2009 I'm glad i bought a van with it on. I honestly don't care how much fuel is uses on weeks like this When i'v been ideling and i press the switch to turn it on i can hear the engine rev higher ever so slightly but the rev counter doesn't move. Link to comment Share on other sites More sharing options...
shark_90 Posted July 1, 2009 Report Share Posted July 1, 2009 I can't remember where I read or heard it, but apparently it used less fuel than the drag created with the windows down does Link to comment Share on other sites More sharing options...
micalee Posted July 1, 2009 Author Report Share Posted July 1, 2009 According to Mythbusters: AC vs. Windows Down Adam and Jamie tackle not so much a myth as what they call an "urban puzzle". The debate arises because both methods of cooling influence a car's fuel efficiency—air conditioning requires a lot of power to run, but at the same time, open windows create drag Revisited in MythBusters Revisited, Season 3, episode 38Myth statement: Running a car with air conditioning on is more fuel efficient than running with the windows down. Tests were performed under varying conditions (55 miles per hour (89 km/h) versus 45 miles per hour (72 km/h)). Also, the 55 mph test was using a computer to estimate fuel efficiency based on air intake, not actual fuel consumption, and showed A/C was more efficient. The 45 mph test consisted of running the tank until it was empty, and showed open windows were more efficient. This experiment—or one like it—is sometimes cited by the Magliozzi Brothers on Car Talk when presented with this question. In a nutshell, it looks like below 55mph, windows open are more economical and above 55mph, AC is more economical. Yahoo Answers also hav quite a few views. Here's one: The answer to your question is MAYBE. The AC unit will increase your fuel usage by around 3-5% if you are on full cooling, but having your windows down instead increases drag. The average "family car" with the windows down will use around 2-3% more fuel up to 50mph, and coniderably more (around 6-7%) above that speed. Your air con unit will top out at using around 5% more fuel. This means that up to 50mph you can keep your windows down, but above 50mph is it actually more fuel efficient to run your air con. Obviously just using your cold air blower will have little or no effect on your economy Link to comment Share on other sites More sharing options...
Tipex Posted July 1, 2009 Report Share Posted July 1, 2009 At work we find that running the A/C on the diesel cars makes no difference, but on petrol cars it's a couple of mpg drop, not enough to worry about really. Link to comment Share on other sites More sharing options...
MrAvant Posted July 7, 2009 Report Share Posted July 7, 2009 In normal weather i used to switch the compressor off (so in this country the compressor was off for about 10 months in the year) but i was told by a mechanic that by leaving the compressor off the seals in the A/C dry-up and crack and then i would loose the gas, hence it would make more sense just to leave the compressor on even if you require heat so that the seals stay moist. True or not??? Link to comment Share on other sites More sharing options...
Tipex Posted July 7, 2009 Report Share Posted July 7, 2009 Yes it is true, so long as you turn the A/C on for a while once a month or so you'll be fine though. Most handbooks now recommend leaving it on or using it frequently. Link to comment Share on other sites More sharing options...
MrAvant Posted July 7, 2009 Report Share Posted July 7, 2009 Ok, so theres no need to have it on constantly........every penny counts!!! Link to comment Share on other sites More sharing options...
PetrolDave Posted July 7, 2009 Report Share Posted July 7, 2009 Ok, so theres no need to have it on constantly There's no need, but with the A/C on constantly you also get dried air in the car so when you have the heater on the windows demist faster on damp days. TBH I can't be bothered with the marginal fuel savings (with an RS4 it's so tiny a small change to driving style makes more difference anyway) so I leave the A/C on all the time to reduce the risk of expensive problems with the compressor - maybe the fuel savings added up will be less than the cost of a new compressor? Link to comment Share on other sites More sharing options...
MrAvant Posted July 7, 2009 Report Share Posted July 7, 2009 So i think this leads us back to the original question, how much extra fuel does the AC use? Link to comment Share on other sites More sharing options...
PetrolDave Posted July 8, 2009 Report Share Posted July 8, 2009 So i think this leads us back to the original question, how much extra fuel does the AC use? IMHO micalee has already answered that: http://www.tyresmoke.net/forum/audi-chat/119428-how-much-fuel-does-air-con-actually-use.html#post1422989 Summary: Air con will increase fuel consumption by 3-5%, but opening windows instead will increase fuel consumption by 2-3% up to 50mph but 6-7% when going faster. Link to comment Share on other sites More sharing options...
DanG Posted July 8, 2009 Report Share Posted July 8, 2009 BMW North America report that running AC saps 7-9hp on their 3 litre petrol engines. Not sure where that would leave mpg - they publish no figures for that. Someone once told me Audis disconnect the AC compressor when full power is required - not sure how that would work though. Link to comment Share on other sites More sharing options...
PetrolDave Posted July 9, 2009 Report Share Posted July 9, 2009 Someone once told me Audis disconnect the AC compressor when full power is required - not sure how that would work though. There's an electrically operated clutch that is disengaged in ECON or when the temperature drops to low (to avoid icing), they just operate that to disengage the compressor when the engine ECU senses a demand for full power. Link to comment Share on other sites More sharing options...
Wizbit Posted July 9, 2009 Report Share Posted July 9, 2009 BMW North America report that running AC saps 7-9hp on their 3 litre petrol engines. I can believe that. i used to have a Vectra 2.5 GSI and i could definitely notice the slight loss of power when the AC was on. In my girlfriends 1.2 Fiesta it is ridiculous and she has to turn off the A/C to overtake people (seriously!) My last two cars have been 3.0 TDI's and to be honest i've never noticed any difference with the air con being on or off with the big engined diesels. Link to comment Share on other sites More sharing options...
PetrolDave Posted July 9, 2009 Report Share Posted July 9, 2009 In my girlfriends 1.2 Fiesta it is ridiculous and she has to turn off the A/C to overtake people (seriously!) That's pretty dire - in my wife's Skoda Fabia 1.2 we usually leave the air con on and it makes very little noticeable difference to the performance. Maybe it's a Ford thing? When I was working for Lotus I tested an Escort Cabrio that we were doing some work on for Ford and you could feel the car noticeably accelerate/decelerate when you turned the air con off/on. But that's just down to sloppy engine management programming, a properly programmed engine management adjusts the fuelling to compensate for the change in load. Link to comment Share on other sites More sharing options...
nicknick Posted July 10, 2009 Report Share Posted July 10, 2009 There's an electrically operated clutch that is disengaged in ECON or when the temperature drops to low (to avoid icing), they just operate that to disengage the compressor when the engine ECU senses a demand for full power. With VAGCOM you can even see this happening -there is a compressor "state" that means it was turned off by the engine. I found this out recently when trying to find out if my compressor has failed. According to VAG com it hasn't , but the electric air con fan isn't running so to avoid the compresor failing by overheating I have been running my car on econ (i.e no aircon) for the last 6 weeks. In that time my av MPG has gone up noticeably from around 38 to just over 41 mpg. Since going over 40mpg I have been driving a little slower - and on a 1200 mile round trip to France in convoy (where the slowest driver sat at 70mph) I averaged 44MPG with no aircon (this was 5 up, boot full of luggage and two bikes on the towbar) . Best I had ever seen on a similar mileage/ driving speed run with aircon on was 42 mpg - so my figures in my car suggest at least a 5% improvement in mpg, and possibly a little higher but that gets muddied by differing driving styles. Link to comment Share on other sites More sharing options...
toby a3 quattro Posted August 9, 2009 Report Share Posted August 9, 2009 5% max as stated above Link to comment Share on other sites More sharing options...
harryg Posted September 6, 2009 Report Share Posted September 6, 2009 My A4 has a screen that tells you how much fuel in litres that takes to power the A/C. Link to comment Share on other sites More sharing options...
Sponge Posted September 19, 2009 Report Share Posted September 19, 2009 (edited) ...possibly a little higher but that gets muddied by differing driving styles. Agreed. I've been recording my mileage, fuel purchases, journeys, since I bought my car in 2005. Earlier this year I decided to turn my Climate Control off to see how it effected the mpg. Up until then it was always on. There are benefits to this even if it isn't hot (demisting windows for example). I have been unable to attribute any change in my calculated mpg to having the CC off. My wife and I share our car and journeys, loads (eg boot full of shopping, roof rack, roofbox) vary so much that it's hard, if not impossible to say with any confidence that having it off increases efficiency. I have to accept that many people have investigated the effects and if they say it does make a difference, then I believe them. However, my father never has his on and he recently had loads of repair work carried out on the a/c system. The garage said one of the probable reasons it was faulty was because he doesn't use it enough. I'm reaching the conclusion that I should just turn it back on again and leave it. I'd rather 'waste' a few % than be faced with a mega-repair bill. Edited September 19, 2009 by Sponge Link to comment Share on other sites More sharing options...
Scotty Posted September 19, 2009 Report Share Posted September 19, 2009 On the latest Audi's - those with Start Stop technology and energy recouperation, they've also introduced some features in the DIS to enable the driver to make decisions about saving fuel. There's an enhanced verision of the gear change recommendation - i.e. recommends when to change up and down but it also pops up certain tips. Along with this is a page on the DIS which shows which accessory is comsuming the most energy and it's expressed in the amount of fuel per hour. It normally shows the AC at the top and whenever I've checked it's showing about 1/8 or 1/4 gallon an hour. So if I'm cruising at 85mph and averaging 30mpg this would mean errrm errrrm that I'm using a bit of fuel but not too much. Can any one work it out? Basically it looks like it's minimal. I think it used to be about 10% of mpg but I'm sure it's improved with technology. Link to comment Share on other sites More sharing options...
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