Air conditioning any model

[deejay]

There are some that say running the air conditioning really reduces the mile per gallon of fuel used. Can anyone comment on this or has anyone ever tested this to see if it is true. I guess it's worth noting that open windows above 50mph can reduce fuel efficiency almost as much as air conditioning. Using the air conditioning for or against? Comments welcome...

[Morr]

In general this is taken to be true. It really depends on the vehicle however. For example the current Ford Focus 1.4 will guzzle the juice if you use aircon, whilst other cars such as Jaguars will return virtually identical figures whether its used or not.
On my 2nd Gen I rarely used it so can't comment on the effect it had, but on my current 3rd Gen I have it on almost constantly.
Initially I did not use it very much but following experimentation I found that it made very little difference, perhaps 1 mpg or so worse off, but that is certainly better than having the windows open at speed as you point out.

On a prior Jag IIRC the manual quoted an open window as decreasing fuel economy by 6% at 50mph, whilst the aircon was reputed to make no difference (I wouldn't know, my aircon didn't work )

[NiftyNev]

No idea how much extra fuel using the air con on mine but I do know the Surf goes not like hot humid days. This is when air con is needed the most but because of the hot humid air the Surf performs poorly and using the air con makes it worse.

Nev

[Morr]

...hot humid days. This is when air con is needed the most but because of the hot humid air the Surf performs poorly and using the air con makes it worse.

Nev

Hot days, hot days, erm, yep I think we had one of them once.

[NFC]

I do not know the exact figures for the Surf but, based on research done some time ago, a "typical" aircon compressor uses 9hp when running. (It is comon knowledge that top speed is reduced when running aircon, so the aircon does consume a noticeable amount of power).

Here's the thing: you don't drive any more slowly with the aircon on, so you are using the same hp to keep the car moving, and adding another 9hp to the engine load to run the aircon, so you WILL burn more fuel.


How much fuel?

The speed of a vehicle increases with the cube of the power supplied, so if a car can achieve 100mph with 100hp, the same vehicle will need 800hp to hit 200mph.

A 130hp Surf does 95 (?) mph, so requires about 50hp to hold 70mph. Add another 9hp for the aircon and you will be burning ~20% more fuel (assuming that engine efficiency does not change as the load changes).

If you do a lot of accelerating/decelerating you will notice less of a difference because you will be using more hp to move the vehicle in the first place.
If you drive everywhere at a constant 40mph, you will see more of a difference.

But that is not the whole story because the aircon compressor does not run at full power all the time, so the impact will be less.

Driving with the aircon on was found to be twice as bad for fuel economy as driving with the window open (and even worse around town) by journalists back in 2003, and car manufacturers do not publish the economy figures got with with the aircon running.

The Toyota demisters are pathetic. Without aircon they do not clear the screen. That is all I use the aircon for on mine, but I'm not paying your fuel bill.

[deejay]

The UK's too cold anyway!

Thanks for the semi-official replies to this thread. It would seem that windows open is a sensible choice on the move and in town maybe air con on. Interesting about the pump using extra HP though. Never thought it to be that high. Not planning to exceed the 100 mph anyway. Court on 30th May for 104 mph on bike so guess plenty of time to tidy up/service the Surf during June/July for me - oops! Wouldn't be so bad but was actually only doing 90! I digress...
Fantastic forum by the way - congratulations to who ever put it together as it's been HUGELY helpful for assistance to a new Surf owner - thanks! May be an idea to sit naked in the vehicle covered in water to assist heat exchange - or maybe not???

[ALZ]

Air con

Today after many days of deliberation I found an air con specialist that pressure tested, re -oiled and re-gassed the truck,until this morning I intended to remove all the components.Well Ive noticed there's been no lack of performance both on the M62 or side roads or increase in diesel consumption.However there's been a dramatic increase in how quick it demists the cabin area.Also on a lesser note it smells nice.So far Ive done 104 miles from re-gassing to doing this message.So far happy and not the lead weight I expected. ALZ

[jamsironwork]

myth busters

my kids where watching an american program on sky called myth busters a while back, on one episode they took two identical trucks with the same amount of fuel then drove them around a test track one with air con on the other with windows open both had cruise control set the same. the windows open truck run out of fuel well before the air con truck

[logey79]

most noticable effect is in my 2.0si mondeo. sitting at idle and put the A/C on and the revs drop by approx. 100-150rpm then goes up to normal idle speed 2 secs later.

its always done this from new, it now has 237,000 miles on it. (and its only had 1 clutch and gearbox replacement, 1 new exhaust system and the alternator went about 5,000 miles ago, other than that just standard servicing and brakes...without doubt the most reliable motor EVER!!!)

[ALZ]

Clear windows

Total miles today 132 very heavy rain this evening in West Yorkshire 4 people in with me stuck on M62 all of us soaked air con on heater set mid way fan on low, clear windows and all comfortable.Compared to my last car this air con is more powerful ?? is it because it was designed to run in a warmer/hotter/humid climate like Japan??.Well I suppose its down to personal choice,windows/air con. ALZ

[phoebelala]

[QUOTE=deejay]There are some that say running the air conditioning really reduces the mile per gallon of fuel used.








There are still more that don't care!

Just drive it like you stole it with the AC on all the time and enjoy! Seriously now. I doubt it it would use a mile of fuel in a whole tank. If its hot or steamed up switch it on. if it aint, don't bother.

Simple.........

Al

[mickeyboy]

I used the aircon almost constantly last summer in Italy, I wouldn't say I noticed many less miles from a tank.