A/C & fuel consumption

roop_the_loop

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Does anyone know of a source of hard facts on whether and how much using air con adds to fuel consumption? I've heard a range of opinions from 'hardly any' to 'a lot', and once I read somewhere that it would be of the order of a few per cent, but all that seems fairly anecdotal to me. Also, surely it must depend on a range of factors like the size/power of the engine, the efficiency (however that is measured) of the A/C unit, the relative difference between the outdoor and indoor temperature, maybe even driving speed, etc.

Today the outside temperature is around 30C, and my interior is set at 19C. :cool: Even on a one-hour-drive the climate control never seems to reach the target 19C, instead it keeps blasting cold(ish) air constantly. But my fuel economy seems if anything a bit better than usual, possibly because of the warm weather and hence the engine being warm pretty much from the start.
 

s5tuart

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Does anyone know of a source of hard facts on whether and how much using air con adds to fuel consumption? I've heard a range of opinions from 'hardly any' to 'a lot', and once I read somewhere that it would be of the order of a few per cent, but all that seems fairly anecdotal to me. Also, surely it must depend on a range of factors like the size/power of the engine, the efficiency (however that is measured) of the A/C unit, the relative difference between the outdoor and indoor temperature, maybe even driving speed, etc.

Today the outside temperature is around 30C, and my interior is set at 19C. :cool: Even on a one-hour-drive the climate control never seems to reach the target 19C, instead it keeps blasting cold(ish) air constantly. But my fuel economy seems if anything a bit better than usual, possibly because of the warm weather and hence the engine being warm pretty much from the start.

I don't know. What I do know is that if it's hot it's on and if it's cold it's on to stop condensation! ;)

(ninja edit; just to add that if you turn the fan DOWN a bit on the hottest of days the AC seems to cool the car better)

This guy knows more than me, but I don't know if he's right or not.........

http://www.airconditioningforcars.co.uk/ACpage05.htm
 
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turbopete

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my A/C is permanently ON.
dad turned it off ONCE and he couldnt see any difference on fuel (even on the dash computer) so put it back on and left it! Now I have the car, I see no reason to change the A/C situation
 

Rappey69

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I hired a smart for two with barely 5000k on the clock.. Outside temp was around 34 and i drove at 50-58 mph.. Air con on full blast.
I barely scraped 30 mpg :shock: over a 400 mile trip...
guess the small engines suffer a lot more than a larger one.
 

prwales

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if instead of having the air con on you wind down the windows...you increase drag and therefore fuel consumption, if its hot use it:lol:
 

Miffy

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as above, and there is also another well known saying thats worth remembering, use it or lose it. if you leave the AC off then the seals will harden and eventually you will have a gas leak.
 

rich599

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my sprinter van has now done 890,000 miles so as you can imagine most days i do well over 500 miles,every time i fill up with fuel i zero the trip computer and i allways get between 500 and 550 miles per tank and this is allways the same with or without the air con on,i have never seen any drop in fuel consumption with the air con on
 
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roop_the_loop

roop_the_loop

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Fully agree with you all - I'm a big believer in the air con myself, and have it on 100% of the time irrespective of the weather or time of year. I even have it on on the rare occasions when I open my windows (daft, I know!). In fact, I can't think of any reason to switch the air con off!

That wasn't really my point, though. What I was hoping to find out was - how much extra fuel am I actually burning (in real hard factual terms) when I have it on? And how do I know that - has someone done some proper research into this?
 

television

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This is in 2 parts.
Car that use the compressor with a clutch, that is about cars till 2002 then these will affect the fuel consumption slightly, on these system the air con should be run once a month to stop the seal from deforming.

Car 2002 onwards use a compressor that runs all the time, the only thing that happens is a valve opens to operate any cooling, any difference in these systems is hard to work out as it is so small, one must bare in mind that in most cases its only the difference in the temp that you are cooling, so most of the time just a few degrees
 

Miffy

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as above, just too many variables to accurately gauge the true cost for all cars with aircon.

No doubt smaller engines will suffer a greater amount than a larger engine. What is the temp outside, what is the target temp. Convertible or full body.

I just leave it set to whatever temperature I feel happy with and leave it. If it costs more, so what...
 

television

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Another thing is climate control and air con are 2 different things
 

turbopete

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Another thing is climate control and air con are 2 different things

arent all MB's fitted with climate control now? im sure mine is climate control, and the ones with the digital temp adjustments are an 'improved' version of climate control (cant think what its all called in the hndbook now, but i will check!)
 

Frontstep

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Does anyone buy a Mercedes for anything over comfort ?
put it on be comfortable.
 

whitenemesis

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Thermatic is the analogue controller version (SA Code 580) and Thermatronic is the digital controller version (SA Code 581). There is quite a difference between the two versions, apart from the head unit.
 

television

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With air con, this is the most expensive to run as it is a system just for cooling and on the very early cars like the 124 it is all or nothing.

Climate control does just what it says and gives you the exact temp that you have set it for, cheaper to run as only the difference to the dialed up temp to the outside air, so on an average summer day and its 25c outside and the car is set for 21c then its only cooling that tiny amount of 4c.
The other advantage of climate control is you can use it in the Winter to dry the air coming in and reduce any fogging of the windows.

But again when you pay say £1500 for climate control and do not use it for any cost reasons, then it does not add up, for you would be hard pushed to measure any cost by running it.
 
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roop_the_loop

roop_the_loop

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Another thing is climate control and air con are 2 different things

Yes, in the sense that climate control is basically a thermostat-controlled air con. Rather than just blasting cold air at you ad infinitum, it tries to reach and then maintain a set point / target temperature. (That's how I understand it anyway.)

Both terms are slight misnomers, in my view, as well as confusing the issue. What we're talking about at its core is the ability to cool air, and then it's just a question of how the cooling is controlled: manually ('air conditioning') or with an automatic feedback mechanism aka. thermostat ('climate control').
 

cleverdicky

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Climate control for cars is that anyway.
For a start there is no humidity option - a significant factor in 'real' air-conditioning.
That said from the little I know, car climate control does indeed balance the set point temperature, with little hysteresis, and it does so by using both cooling AND heating at the same time to achieve it.

Where as the simpler thermostat option just blasts either (hot/cold) air which ever option its set on until it achieves set point temperature.
Usually with a wider hysteresis and overshoot.
 

d215yq

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All i know is aircon in cars, trains, buildings, planes is the biggest cause of coughs, colds and dry mouths. Firstly because when you get in and out of them your body has to adjust very quickly to the temparature change which it is not used to doing and secondly because the air con air is much dryer and thus dries your throat/mouth out causing all sorts of temporary respiratory problems.

Luckily i don't have A/c on my w124 so don't have to put up with passengers trying to put it on. even 35 degrees c and windows down/sunroof open is far more pleasant.
 

whitenemesis

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All i know is aircon in cars, trains, buildings, planes is the biggest cause of coughs, colds and dry mouths. Firstly because when you get in and out of them your body has to adjust very quickly to the temparature change which it is not used to doing and secondly because the air con air is much dryer and thus dries your throat/mouth out causing all sorts of temporary respiratory problems.

Luckily i don't have A/c on my w124 so don't have to put up with passengers trying to put it on. even 35 degrees c and windows down/sunroof open is far more pleasant.

It's a view of course but I don't hold with this. Cold and coughs are caused by viruses. Dry mouths caused by breathing through the mouth instead of the nose. |As for thermal shock, the skin may well experience rapid temperature changes but the body core temperature will only be affected minimally.

The biggest cause of the spread of coughs and colds is travelling in confined spaces, being in close proximity with infected persons. "Coughs and sneezes spread diseases!" ;)
 

d215yq

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It's a view of course but I don't hold with this. Cold and coughs are caused by viruses. Dry mouths caused by breathing through the mouth instead of the nose. |As for thermal shock, the skin may well experience rapid temperature changes but the body core temperature will only be affected minimally.

The biggest cause of the spread of coughs and colds is travelling in confined spaces, being in close proximity with infected persons. "Coughs and sneezes spread diseases!" ;)

You are of course right about viruses, but quick changes to body temperature reduce the bodies resistance to such viruses, which is a more improtant determiner as to whether you'll get a cold or not...here, where no one has heating or air conditioning the time for colds is not the winter weeks it hits zero degrees (because the flats are all the same temp without heating so you are always in the same amount of clothing/same temp),but the spring and late autumn when the night/day temp and temps of public transport (platforms hot, trains ice cold and a/c) vary widely and quickly.
 

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