Does air con really eat your fuel?

patman99

I used to own a Renault Espace and the owners book had loads of info on fuel use. According to their tests driving at 30mph with one window down increases fuel consumption by 8%, and at 70 mph by 15%.

darich

In my experience of air con there is no discernable difference in fuel economy.
however on my 1.8 Celica if cruising at 40-50mph in 6th gear, flicking on the air con you could feel the car hesitate as the pump kicked into life.
On my other cars with air con (bmw z4 3.0 and currently Audi A4 2.0T) I didn't/don't notice any difference.

I believe that a smaller engined car may notice a difference since it's more effort to pull the car along and work the air con. For a larger engined car it's less effort so I think the air con has a much smaller effect on the economy.

Coveredinbees!!!!

My aircon has stopped working and it's frankly rubbish not having it, cars like an oven even with the windows open.

shown73

I've tried this on long, boring autobahn trips, and as far as 1.8 Mondeo is concerned, there is a noticeable difference with aircon on. The fuel computer drops from low 40's to high 30's. Annoyingly, it means that I can't quite make it to Calais on a tankful, which of course means overpriced motorway fill-up.

johnnyroper

Strider590 wrote: »

It I think depends on whether the aircon is driven from the auxiliaries belt or not, if it's fully electric....

Like for example EPAS (Electronic Power Assisted Steering) which uses an electric motor instead of the belt driven hydraulic pump system used in old school PAS.

Anything extra that the engine has to physically move, will always have an effect on fuel consumption... Electrically driven devices have very little negative effect.

what a load of rubbish,even if the A/C on a car was electric motor the fuel consumption would be same if not worse than driving it via the ancilliary belt.
have you ever put on rear electric window and blower motor when at idle and noticed the load that is put on engine???

as for original posters question if the A/C is left on all the time you will not notice a difference mine is on all year round,if you drive with window open it will probably use more fuel than the A/C due to excessive drag etc.
furthermore you are buying an auto gearbox so the main reason for poor mpg will be as a result of that.

vaio

darich wrote: »

In my experience of air con there is no discernable difference in fuel economy…….I believe that a smaller engined car may notice a difference since it's more effort to pull the car along and work the air con. For a larger engined car it's less effort so I think the air con has a much smaller effect on the economy.

Yep, I once had a cheap hire car out in Crete and driving in the inland hills it was noticeably faster if the air con was off.

I suppose a compressor takes 5 bhp to drive and if it’s attached to a 20 bhp engine then when you turn it on you lose a really noticeable 25% of your power.

If it’s attached to a 250 bhp engine then you lose an insignificant 2% of your power

HonestJon

I agree with what gloomendoom has said, 5 minutes once a week will keep the gas topped u. Ive never found it makes much difference to fuel consumption on or off to be honest.

Pincher

I was told if you don't run the air-con once a week, the bearings tend to seize up. Another problem is mold, which the condensation tends to wash away if you use it regularly.

iolanthe07

Pincher wrote: »

I was told if you don't run the air-con once a week, the bearings tend to seize up. Another problem is mold, which the condensation tends to wash away if you use it regularly.

The main problem is the seals drying out.

Altarf

It is the wrong way to think about how much fuel aircon uses, by considering its impact on mpg. The sensible way to think about it, is how much fuel does it use to run per hour.

For example, if you have a 30 mile journey to make, the aircon itself will use 1/2 the amount of fuel if you drive at 60 mph rather than 30 mph, but obviously the mpg you get at 60 mph will be very different to 30 mph.

So trying to calculate the effect of aircon on mpg is fairly complex, and even when you succeed with the maths, will leave you with a number that doesn't make much sense at the end.

Going back to the fuel use per hour, figures that I have seen from one of the aircon manufactures (sorry can't find the link at the moment) suggest that the average aircon unit on a car on a summer day in central Europe will use about 0.4 litres of fuel per hour.

To give you an example of the confusion that you get if you try to think of it terms of mpg figures. Iif you take that 30 mile journey at 60 mph, and do it in 3 different cars, which without aircon would get 50mpg , 40mpg, and 30mpg. If you turned the aircon on at 0.4l/hour the effect of the aircon on mpg would be 7% on the 50 mpg car, 6% on the 40 mpg car, and 4% on the 30 mpg car. But even though you have vastly different percentages, they have all used the same amount of fuel to power the aircon.

So about 45p per hour is a number that makes more sense to me than x% change in mpg.