Aircon or open window? Fuel cost

FirstClassMale

I have me first car with air con. I have never felt the need for it before and would have much rather had a sunroof.

The other day, I got into the car and pulled onto the dual carriageway where I opened the back window for a few minutes to suck out the hot air. Now I know that air conditioning uses fuel but so does driving with ones windows open. I reckon I should open the windows at high speed and use the air con when driving slowly in town but what is the difference in fuel usage?

I'd be keen to hear views on this as the price per litre of fuel has probably gone up since I started writing this.

zappahey

FirstClassMale wrote:

I reckon I should open the windows at high speed and use the air con when driving slowly in town but what is the difference in fuel usage?

This page from Florida suggests that it increases fuel consumption by between 5% and 15%. http://www.fsec.ucf.edu/Pubs/energynotes/en-19.htm

carl310166

Don't forget,you must use your air con for at least 30 mins a month,even in the winter,otherwise the seals in the system will dry out.

http://www.honestjohn.co.uk/faq/faq.htm?id=14

Chris_VRS

I personally never turn the A/C off!....apparently it's actually more fuel efficient to have the A/C on rather than the window open on the motorway etc...and obviously a lot quieter!

Try both and see if you notice a difference!

Wig

Don't know any stats but I would assume it's cheaper to drive with the windows open especially at lower speeds. On the motorway you can have the window open a small amount and get a big blast of wind.

You can also consider having the fan on cold through your vents. I remember the old cars were much better, no fan required the vents were just tubes connected to the outside open one of those and you got a blast of cool air, these days you have to have an electric fan running!

I have A/C I never turn it on, apart from once every 2 - 4 weeks.

Lob_Rockster

I think aircon uses more fuel on cars without power sources sufficient to effectively drive the system....my car has climate control and I'd say it doesn't use more fuel. Also what cost then would loud music and xenon lights be to you?

Altarf

Lob_Rockster wrote:

I think aircon uses more fuel on cars without power sources sufficient to effectively drive the system....my car has climate control and I'd say it doesn't use more fuel.

The power (and thus the fuel) needed to operate the aircon will be the same for a big car or small car.

For example if the aircon used a litre per 200 miles to run the aircon (plucking numbers from the air) you might not notice the 3.5% increase in fuel consumption on a car that gets 30 mpg but you would probably notice the 7% increase on a car getting 60 MPG. The fuel used is the same in both cases though.

stevemcol

Tested this on a motorway during a boring drive. Wasn't able to measure the difference using instataneous or average MPG meter (aircon on/off).
Not very scientific but it convinced by it costs very little to use the aircon.

If you never use it, the refrigerant gas may dump with significant cost to replace.

mistyarthur

I remember reading a few years ago that having air conditioning on uses around 19mpg more than not using it. Don't have a clue about having the windows down though!
I only use it occasionally because once a car gets more than a couple of years old it doesn't tend to work very well and for 19mpg it's not worth it.

chrisw

mistyarthur wrote:

I remember reading a few years ago that having air conditioning on uses around 19mpg more than not using it. Don't have a clue about having the windows down though!
I only use it occasionally because once a car gets more than a couple of years old it doesn't tend to work very well and for 19mpg it's not worth it.

19mpg? Probably no more than 2-3mpg, which is likely to disappear within the natural fuel consumption variation anyway.

Having said that, I was hired a Suzuki Swift in Spain with aircon, but I had to turn the aircon off to get up a hill.

headcovers

mistyarthur wrote:

..............
I only use it occasionally because once a car gets more than a couple of years old it doesn't tend to work very well .....................

My car is a T reg (1999) and hence is 7 years old and the air conditioning climate control works perfectly. I wouldn't be without it.