Air Con On or off?

castle96

ll year long. Does it use more fuel? I know the argument re seals, but what about mpg

Herzlos

Everything consuming power must get that power from fuel. How much will depend on too many factors to give you an answer.

Try running with/out and see what happens.

Ebe_Scrooge

Herzlos said:

Everything consuming power must get that power from fuel. How much will depend on too many factors to give you an answer.

Try running with/out and see what happens.

That's it in a nutshell, really.

Yes, having it on will use more fuel.  As Scotty was so fond of saying, "ye canna change the laws of physics".  If it draws an electrical current, that electricity comes from burning fuel.  If it puts extra load on the engine, that'll burn more fuel.

The question is whether it'll make a significant (or maybe even "measurable by the average person") difference.  I know years ago when aircon first became "commonly fitted" to cars, it did make quite a difference - at least, that was my experience.  I suspect that probably technology has improved, and the difference may well be less marked now.  But yep, all you can really do is suck-it-and-see, to see what a difference it makes to your particular car.  If it's a marginal difference, or maybe even too small to really measure, then you've got your answer :-)

Username03725

All cars are different, but try this.

Reset your Current MPG on the display then set off on a journey, trying to maintain as constant a speed as poss and ideally on a long straightish level road. Good luck finding one in the UK though

Once the Current MPG is fairly stable, switch the air-con on. Acc to some in the old days it added 10-15% to fuel consumption with the added load. I've never seen that, and in higher powered cars the % of engine power needed to run the aircon is much less than a wheezing 1.2 in a little city car. On my 2.0 diesel the MPG doesn't change when the aircon is switched in or out. What does change it is accelerating harshly.

photome

yes it probably uses more fuel, but mine is on all year round on all cars I have ever owned with air con/climate control

datostar

After a very large bill for replacing a seized aircon compressor on a previous car I leave it on all the time (per manufacturer's recommendation) on my current one. 12 years old now and only required a single recharge in all that time. 

Car_54

The "10-15% in the old days" was probably alarmist, even then.
These days, most articles I've read suggest around 2%.
One of the mags did some testing some time ago, measuring the real-life effects of various "fuel-wasting" practices (air-con, roof rack, open windows, load in boot, etc). Air-con was far from the worst offender, and opening the windows instead probably used more fuel.

Ebe_Scrooge

datostar said:

After a very large bill for replacing a seized aircon compressor on a previous car I leave it on all the time (per manufacturer's recommendation) on my current one. 12 years old now and only required a single recharge in all that time. 

That kind of ties in nicely with the OP's original question.  I don't think anyone would dispute that if the aircon never gets used then it'll seize/seals will leak/it'll break in some manner.

But what if, in those 12 years of being constantly switched on, it's cost you an extra £100 in fuel all told?  Or an extra £500, or £900, or whatever the figure may turn out to be?  It's possible that, had you not used it, you'd have saved enough in fuel costs to more than cover the cost of the compressor.

Aircon - or anything that draws a current or puts extra load on the engine - will use extra fuel.  It has to, it can't not.  The question is how much - it way well turn out to be negligible, possibly even barely measurable for all practical purposes.

Obviously it would take some working out to see how much extra fuel you'd used, and I don't doubt that all cars are different.  But it's food for thought :-)

ElefantEd

On our electric car the guessometer of range usually subtracts a couple of miles for having the aircon on compared with not, a difference of 1-2%. I doubt it would be any worse (or better) for any other type of engine.

Ectophile

If you're going on a fast journey, then using the aircon can be more efficient than opening the windows.  Open windows increase the drag.

Herzlos

Car_54 said:

The "10-15% in the old days" was probably alarmist, even then.
These days, most articles I've read suggest around 2%.
One of the mags did some testing some time ago, measuring the real-life effects of various "fuel-wasting" practices (air-con, roof rack, open windows, load in boot, etc). Air-con was far from the worst offender, and opening the windows instead probably used more fuel.

I remember reading something a while back that it was better to have the windows down at low town speeds and Aircon on at higher speeds due to drag from open windows.