I’m convinced that, due to its automatic nature, the climate control makes little difference to the overall mpg in a typically British climate. However, to provoke a worst case response, I tried the following due to commuter boredom.

After running on automatic and 20°C for about 15 miles, and cruising at a steady speed, I turned the aircon off and on several times and observed the instantaneous mpg. No difference seen- so I assume the aircon was not actually working hard and the internal temperature had stabilised.

I then turned the temperature down to minimum and again observed the effect of turning the aircon off and on. A 3-4mpg decrease in the instantaneous figure was seen when aircon was on. Not as bad as some people are reporting though.

I’ll leave mine on automatic.

Air con must make a difference to to cars mpg as you are using power from the engine to run the aircon. However I have never noticed a big change on the MPG in any of the Skoda diesels I've owned from the winter to summer, so how bigger difference there is I'm not sure.

Some say the mpg difference is more noticable with a petrol engine. I'll get the Wife to test it in here 1.2 petrol Fabia with the climate control.

As you state the difference is when the aircon is working. Hence the 3 to 4mpg effect will only be for part of the journey unless it is a very hot day. I used to have my on the economy setting most of the time but then left it in auto for a while. Saw no real difference in mgg or miles used between fills so keep it like that now.

That's interesting to note. I tend to leave mine on 'Econ' unless I actively require it.

Might just leave it on full auto then, do a few my usual journeys and observe the effect (if any).

Cheers,

Steve

I run the climate on auto and despite this the compressor has recently failed. The dealer is waiting for a compressor as they are on back order. :wonder:

I tried the on and off thing with my Octy’s Climate control and didn’t notice much, if any real difference. I guess you don’t see anything at first because the refrigerator bit is still nice and cold after you first turn it off, but I think I saw a slight decrease when I turn the chillier on after having it switched off for a while (I think that makes sense). I never turn mine off though, as I paid good money for the other benefits, like dehumidifying and filter, so it seems silly not to enjoy it, even if it cost a little more to run.

Personally I have never been able to put a figure on it by testing it as above, but it doesn’t seem to use more than a couple of mpgs as far as I can guestimate I have read figures like 10%, but I have never seen anything like 4-5 mpg drop whilst driving. Perhaps those figures are for mixed driving, not motoway driving where there is lots of aid running though everything?

It tends to have a greater effect if you are doing short journeys, as the a/c is having to do a lot of cooling each time you use the car to get the cabin temp down.

On longer journeys, the a/c is just maintaining the temp after the intial cool down, so the overall effect on mpg is less.

I'm doing a test today on this - run to Devon - last time on auto got 57mpg average.

This time without it on.............?? :wonder:

It's a tough thing to work out because MPG is affected by so many variables - including weather and temperature.

In my Fabia I get slightly better miles per gallon overall in summer than in winter, without using aircon very much at all.

But if I did used aircon, assuming I used aircon regularly in summer months, even if I got the same mpg figure as in winter, the two effects (better mpg from warm weather versus worse mpg from using aircon) might cancel each other out and I wouldn't see much difference.

I'm doing a test today on this - run to Devon - last time on auto got 57mpg average.

This time without it on.............?? :wonder:

But suppose for example you had a 10 mph tailwind last time but a 10 mph headwind this time, would you know about it? It would probably make a noticeable difference to the mpg... It's hard to assess mpg reliably from individual runs.

It doesn't seem to make much difference if any to the MPG and it'll make the journey a lot more comfortable so for me it makes sense just to leave it on auto.

In the heat 40 and cold - 10 we have here the economy setting is useless, and I get fogged up.

Aircon will have a bigger difference on a small engine than a large one, as it will use a proportionally larger share of the available power; on a 1.2 it may feel like a turbo has cut in if you turn the aircon off when going up a hill.

In my 165bhp, 2,5L engine it makes 2-3 mpg difference when I switch it on, but I have not measured it over a long journey as I do not make that many.

Turn it off and open the drivers window about an inch, that will keep your windows clear most of the time, its only once in a blue moon it get hot enough to use it

Mythbusters on some random sky channel did this in a Yank jeep thing think they did laps of a track with air-con on air con off and windows open and car with no air con and windows up! ... usefully i cant remember what they found though! hehe

I normally use Econ mode unless it's roasting and usually get about 58mpg on my way home from work this time of year. My trip home from work today, with Auto on, was just a smidge over 50mpg.<BR><BR>Not exactly a very scientific exercise though......

Turn it off and open the drivers window about an inch, that will keep your windows clear most of the time, its only once in a blue moon it get hot enough to use it

That'll then increase drag though, with the window open. So you don't get anything for free!

I seem to recall an experiment when they did a comparison against driving with the windows open, versus the use of AC. Think the AC was more efficient.

Steve

Mythbusters reckon:

The fundamental flaw in the MythBusters' test was that the point where the drag becomes powerful enough to inhibit a car's performance with windows down was inside their 45–55mph margin at 50mph. Going less than 50mph it is more efficient to leave the windows down, but going greater than 50mph it is more efficient to use the A/C.

If you have maxidot, you can change the consumption units from mpg to l/km. When you are stopped it shows l/hr.

I remember being stuck on a Belgian motorway in summer, and it made a difference to the consumption when you turned off the AC.

I tried it just now by turning the temp to low. With AC on it said 1.0 l/hr. With it off 0.7 l/hr.

Interestingly, with it set at 21C it was using 0.8 l/hr with AC on, 0.7 l/hr with AC off. The outside temp was showing as 18C

Edited 10 September, 201015 yr by jrp

I seem to recall an experiment when they did a comparison against driving with the windows open, versus the use of AC. Think the AC was more efficient.

Yes, I believe the break even point is around 20-30mph - any faster and the drag of having windows open makes using air-con more efficient.

I normally open the windows as I set off to initially (quickly) cool the car down, and then close them and crank up the air-con as soon as I'm up to speed.

Considering the fact that the trip computers are nigh on useless (10 - 15% out at best). You'd need to do 2 tankfull identical journeys, on days with identical weather, traffic conditions etc etc to find out.

You need to use the air con quite often for the sake of the system anyway. And if you are using climate control, unless you have a very low setting, the air con element (i.e. the compressor etc) is only going to cut in when the cabin is above your setting, so even if you leave it on air con, I imagine it is not "air conning" all the time.

I should have said only the drivers window open an inch causing no drag, but it acts as a chimney drawing out any condensation

It makes no difference.

Leave it on Auto all the time

You need to use the air con quite often for the sake of the system anyway. And if you are using climate control, unless you have a very low setting, the air con element (i.e. the compressor etc) is only going to cut in when the cabin is above your setting, so even if you leave it on air con, I imagine it is not "air conning" all the time.

Not so much these days. We havent run clutches on the a/c systems for years so the system is always running keeping the gas and oil moving around the system,

Obviously it does a bit as the refrige gas compresor takes power via the aux belt and that could be quite a few hundred watts I seem to recall.

So this could represent a one or 2 percent increase in the output of the engine required so I would expect that might translate to a half or one mpg less.

Economy setting elimnates the compressor running and therefore system relies on purely mixing external air. If the external air is dry and 15 degrees or less then air con should not be needed.

I tend to switch it off ie go to economy after intial clearing operation and then put it back to auto if the temperature outside creeps up to 20 degrees or over during the day and that off again when outside temperature drops to 18 or so. I am just annoyed that Skodas do not seem to have 16 or 17 degrees on the system like Audis and SEATs do what is that about (when I am doing a short trip and wearing multiple layers)?