Air Con 'charging' question

Ultra_Extreme · 23 Apr 2006 at 15:11

Dogbreath said:
Yet another OcUK scientist manages to trash the laws of thermodymanics in a single sentence...

try it out....bet you have to lie

Clarkey · 23 Apr 2006 at 15:28

what the hell are you talking about, turn the compressor by hand, what while the engine is running??

Its fairly obvious that once the engine is off the magnetic clutch is not energised and as such by turning the pulley it is just freewheeling.

Seriously, learn something before trying to teach us crap.

Ultra_Extreme · 23 Apr 2006 at 15:39

Clarkey said:
what the hell are you talking about, turn the compressor by hand, what while the engine is running??

Its fairly obvious that once the engine is off the magnetic clutch is not energised and as such by turning the pulley it is just freewheeling.

Seriously, learn something before trying to teach us crap.

When its out of the car dipweed. Although by hand with the engine running could get nice and messy

. Im not arguing the principles of resistance vs fuel consumption, simply that in air con systems ive tested this theory on there is either non or a wholly negligable difference.

Dandle · 23 Apr 2006 at 15:46

Ultra_Extreme said:
When its out of the car dipweed. Although by hand with the engine running could get nice and messy . Im not arguing the principles of resistance vs fuel consumption, simply that in air con systems ive tested this theory on there is either non or a wholly negligable difference.

It makes a difference on my T4 but not much(.5-1mpg). Smaller engines are more effected by the use of AC though. On the T4 at WOF the AC automatically disconnected to give the engine maximum power, it wouldnt be designed to do that if there was no effect from it being on.

Freefaller · 23 Apr 2006 at 15:49

Ultra - watch the attacks please.

Ultra_Extreme · 23 Apr 2006 at 15:57

Clarkey said:
.....

Seriously, learn something before trying to teach us crap.

Freefaller said:
Ultra - Watch the attacks please

be fair dude, and Clarkey its meant in jest not agressivley.

Ultra_Extreme · 23 Apr 2006 at 16:01

Dandle said:
It makes a difference on my T4 but not much(.5-1mpg). Smaller engines are more effected by the use of AC though. On the T4 at WOF the AC automatically disconnected to give the engine maximum power, it wouldnt be designed to do that if there was no effect from it being on.

well as ive said, over half a tank of fuel ive seen no PROVEABLE difference, its been up and down although ive only run it idled and around a private loop in 2nd. the difference in real world fuel consumption was 0 +- 2 mpg regaurdless of AC activity.

Dogbreath · 23 Apr 2006 at 16:30

Unless you are subconciously driving more slowly with the aircon on, there is no-way that it can't use more fuel. It might not be a very large amount, but the compressor requires power to drive it and that power comes from burning fuel.

If you are refering to the Mythbusters program I think you are, then they simply showed that at 45mph the Aircon used more fuel than having a window wound down, contary to the popular myth. At higher speeds the result would probably be different. In any case, they used an SUV with the aerodynamics of a barn door so the result was (in usual Mythbusters style) very inconclusive IMO.

Dave L · 23 Apr 2006 at 16:36

What a great thread!

An AC compressor requires anywhere from 10-15BHP to drive it - modern variable output compressors are much more efficient than yesteryears fixed displacement compressors.

Modern day cars will show little or no fuel consumption penalty whereas older cars will......

Foghorn Leghorn · 23 Apr 2006 at 18:03

Ultra_Extreme said:
well as ive said, over half a tank of fuel ive seen no PROVEABLE difference, its been up and down although ive only run it idled and around a private loop in 2nd. the difference in real world fuel consumption was 0 +- 2 mpg regaurdless of AC activity.

Running the aircon on/off will make a difference to any vehicle it is fitted to regarding fuel consumption.

You cannot test it accurately by monitoring your mileage over half a tank of fuel

, as the fuel consumption difference isnt that great.

I see about 1-2 mpg difference on my 406 HDI. I tried it by holding a steady speed on the motorway, flick aircon off see mpg rise, flick on see it drop, etc etc each time change is about 1-2mpg.

Fog

The_Dark_Side · 23 Apr 2006 at 21:09

as i'm not an air con engineer and it seems the following member is, i'll bring my main concern to the front and see exactly why i'm wrong.

Dave L said:
An AC compressor requires anywhere from 10-15BHP to drive it - modern variable output compressors are much more efficient than yesteryears fixed displacement compressors.

Modern day cars will show little or no fuel consumption penalty whereas older cars will......

of course you are correct in that modern compressors are much more efficient, then unless we're talking 100% efficiency (and you have my mail addy in trust to explain how they accomplish perpetual motion) then the compressor STILL adds extra load to the rotational parts of the engine.how much load is another question altogether as is how much fuel consumption is increased but it is increased load of some description.
more load, whether it's on the engine or on the vehicle itself in the form off added weight means the engine has to work harder to maintain the same RPM and as such will require more fuel to do so.

neil-ste · 9 May 2006 at 20:41

So has anyone actually tried one of those Halfords kits then?

The air con on my newly acquired Mondeo is a bit weak at best.

Steve · 9 May 2006 at 21:04

Mine is a bit weak which is annoying as I only just got the thing, I did test it but it was a cold day so it must have been artificially cold

Anyone recomend any good auto aircon places in the Brighton area as *** internet is sucking a bit for any help in that area

lordrobs · 9 May 2006 at 21:07

Well if nothing else Ultra, you have made me chuckle!

Seriously, if you hit the air con button on your 306 you don't notice the drop in revs (which is almost instantly compensated by the ecu) ? That is caused by an extra load on the engine. There is some sort of clutch mechanism that disengages it when its not in operation.

csmager · 9 May 2006 at 21:14

Dogbreath said:
If you are refering to the Mythbusters program I think
you are, then they simply showed that at 45mph the Aircon used more fuel than having a window wound down, contary to the popular myth. At higher speeds the result would probably be different. In any case, they used an SUV with the aerodynamics of a barn door so the result was (in usual Mythbusters style) very inconclusive IMO.

Not only that, the thing had a huge engine. I doubt an Air Con unit would have much of an impact on something that already guzzles that much fuel.

Steve · 9 May 2006 at 21:44

in both my m3s I can see the rev counter drop briefly on idle when I put the air con on

southy1978 · 9 May 2006 at 23:40

Steve said:
Anyone recomend any good auto aircon places in the Brighton area as *** internet is sucking a bit for any help in that area

Place i work at does check over+regas for £70+the dreaded, email in trust if you want to mail me for details.

vanpeebles · 9 May 2006 at 23:47

ive never gotten round to regassing mine, tempted to strip it all out to save weight

S@njay · 11 May 2006 at 13:25

So many mixed feelings about air con!

My car air con is not cold at all! Its a V-reg mondeo, would it be worth it to recharge it?

I want air con so badly! Looking around garages in Rugby, not many people do it!

OllyM · 11 May 2006 at 13:37

It's likely that it's the condenser, to be honest.

Mine was recharged and pressure tested, it passed, but a month or so later, it dumped all the gas.

I'm about to get it fixed because I just can't stand not having it in this heat, but £200 + VAT for a condenser fitted