Do you notice A/C using up more fuel in your car?

Oli

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I've not really noticed any great difference in fuel consumption for using the A/C in my last couple of cars, it doesn't seem to make any difference to fuel economy or performance in the E55, but then it's such a big tourquey engine that driving the compressor isn't going to make it break a sweat, I imagine most of the bigger engined petrols and diesels are the same, when I use a 1.6 Golf though it does use noticeably more fuel if you turn it on although performance isn't affected, so just wondering if other people notice it in their cars or not as I would be interested to know the sort of engine size/power output where the difference becomes un noticeable.
 

Bobby Dazzler

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Never noticed any car I've had. The only cars I've owned with aircon have been V6 or forced induction though. Maybe I'd have noticed it more in my trusty Vauxhall Nova, had it been fitted with AC. :D
 

GP801

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Nearly always keep the aircon on on ours. It does not seem to make a significant difference to fuel consumption.
 

Dryce

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I've not really noticed any great difference in fuel consumption for using

Never noticed in any car I've had. But I always leave the system on auto at a set temperature of 21.

A lot of people don't - they use the system flat out and manually play with it. They just don't understand that the automatic setting will normally work a lot better.
 

Fatbloke

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My last few cars have been diesels and i have always left it set on auot, not really much difference to performance or fuel consumption unless its really hot and its working hard.
I can feel it a little in my current car, 180 kompressor, but nothing dramatic. I tend to have the roof open as soon as its sunny anyway.
 

The mallard

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I previously had always left mine on all the time (W203) but in the last few months and few thousand miles, have turned it off in the cooler weather and have noticed the overall mpg has risen by just over 1mpg, and as I had not reset it when changing technique I can only asume the oveall increase will be somewhat better,maybe 2-3mpg
 

snoop51

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Never noticed in any car I've had. But I always leave the system on auto at a set temperature of 21.

A lot of people don't - they use the system flat out and manually play with it. They just don't understand that the automatic setting will normally work a lot better.

+1 I find it somewhat annoying when SWMBO gets in my car puts the aircon into separate zones and turns hers down to LO. Despite my best attempts to educate her that 21 Degrees is 21 Degrees regardless of what the outside temperature is.:wallbash: I'm thinking of gaffer taping her hands to the door handle then she can't mess with it.

No I haven't noticed climate control making a blind bit of difference to fuel economy. SWMBO used to have basic aircon (cool function only) on a Mazda MX5 which you could here the engine bog down at tickover when you switched it on. So I too think it is engine power / size dependant.:)
 

Wizeng

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+1 I find it somewhat annoying when SWMBO gets in my car puts the aircon into separate zones and turns hers down to LO. Despite my best attempts to educate her that 21 Degrees is 21 Degrees regardless of what the outside temperature is.:wallbash: I'm thinking of gaffer taping her hands to the door handle then she can't mess with it.

I have exactly the same problem, also I tell her the harder she holds onto the door handle the better i can get round the corner:devil:
 

MercFanUk

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Never noticed a difference between on/off in any car, including on long journeys.
 

John

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I don't notice any difference in my E55K but it is very noticeable in my other half's Jazz (1.4).

So much so that the EMS increases the revs by about 500rpm when the compressor is running.

I normally leave mine off in the Summer when it is nice as I prefer to have all the windows open so I can hear the exhaust.

I turn it on to 19 and leave it if for any reason I have to have the windows up.
 

scottishman2

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I remember driving through Death Valley in Nevada in a hired Chevrolet --- as we left the lowest part and headed up the hill it was 45 degrees C... and a big sign said "turn off your Air Conditioning before climbing the hill"..... never heard my wife use that expression before but I decided that I should obey her and leave it on....... I reckoned it was safer to use the extra fuel....
 

scumbag

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The rollerskate engine note changes at idle when you press the flimsy and cheap button to engage the A/C.

Never noticed it in any Merc, but it also did in a PUMA a million year ago way back in the last century.

My old Scooby knocked it off if you were pressing hard on the pedal so it didn't eat some power you were requesting.

Have never noticed if it uses more fuel tho. never realy checked.

I would assume, if it does, the smaller engines might notice it more, but the fuel efficiency of the largers engines is a bit less so probably not as much.

far less than leaving the windows down though.

Am now wondering if a fabric roof uses more fuel than the hard top?:doh:

I did like the SLK's when I put the A/C on with the roof open and people, in the car, used to think it wouldn't work, but it blew cold air at you and it did work. That was my cure for global warming so you can blame me for the last few bad winters...sorry....have moved since....deal with it.:ban:
 

Timper

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I thought the line that "it uses more fuel if you put the AC on" was always a misleading way of putting it?

I thought the correct explantion is that using the AC takes up approximately 2-4 horse power of the engine so it can't deliver all of it's power to the wheels, but it's not actually consuming any 'more' fuel.

In other words, say you were driving your car flat out around a race track trying to get the fastest times lap for example, you would benefit from all the engine power if you kept the AC off whereas during normal road driving, it makes none or little difference.

Please do correct me and put me right if this is not the case, i'm no expert - that is just how i undesrstood it to be.
 

Dieselman

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I remember driving through Death Valley in Nevada in a hired Chevrolet --- as we left the lowest part and headed up the hill it was 45 degrees C... and a big sign said "turn off your Air Conditioning before climbing the hill"..... never heard my wife use that expression before but I decided that I should obey her and leave it on....... I reckoned it was safer to use the extra fuel....

You would have regretted that if the cooling system had boiled up.
 

Dieselman

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I thought the line that "it uses more fuel if you put the AC on" was always a misleading way of putting it?

I thought the correct explantion is that using the AC takes up approximately 2-4 horse power of the engine so it can't deliver all of it's power to the wheels, but it's not actually consuming any 'more' fuel.

In other words, say you were driving your car flat out around a race track trying to get the fastest times lap for example, you would benefit from all the engine power if you kept the AC off whereas during normal road driving, it makes none or little difference.

Please do correct me and put me right if this is not the case, i'm no expert - that is just how i undesrstood it to be.

So where does the extra energy come from?

Of course running an additional load of 2-4 Hp consumes more fuel. Ye canna beat the laws of physics Capt'n..
 

John

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One way to illustrate it might be this:

Car with 100BHP at the flywheel on maximum throttle is using 100BHP which means it is using 100BHP and the required fuel to meet that (= X).

With the air con on, say it uses 5BHP, you are still using the same amount of fuel (X) as you are still using the full 100BHP, but you only have 95BHP now because the compressor is using 5BHP.

However, cars with a lot more BHP to start with means as a percentage of the total power available, e.g. 476BHP, aren't so noticeable because 476BHP and 471BHP are the same when it comes to a driver's experience.
 

Dieselman

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It still needs more fuel to power the A/c, especially since most driving won't be using anything like the maximum available power.
Cruising at say 60mph, requires about 16bhp, so the A/c load equates to an additional load of 12-25%.

Just driving with the lights on uses approx 1.5mpg more fuel.
 

Mactech

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So where does the extra energy come from?

Of course running an additional load of 2-4 Hp consumes more fuel. Ye canna beat the laws of physics Capt'n..

I have tried and have yet to succeed!:rolleyes:
Modern systems tend to limit the amount of work done by the compressor so that air conditioning doesn't use that level of power all the time like older 'non smart' systems.
But, there is no getting around the fact that energy in used to cool the inside of the car...and that energy comes from your fuel tank.
In a modern Mercedes with no great 'delta' between your interior temperature and ambient, the increase in fuel consumption is very small....but still there:(
Most people could save a whole bucket of fuel by looking up 'conservation of momentum'....:devil:
 

Dryce

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Cruising at say 60mph, requires about 16bhp, so the A/c load equates to an additional load of 12-25%.

But is the A/C compressor running continuously at full load. It presumably runs at a given duty cycle (at least that's the impression I have) to maintain temperature.

In the UK I reckon that it's a low % on my climate control system once its settled.

So if at 100% it adds 12-25% then at say 10% or 20% load/duty it's only making an overall impact of 1.2% to 5%.

Which is why a sensible climate control setting in normal UK ambient conditions doesn't make that much of an impact. Those running a manual aircon setup at a higher load will see a different picture (and possibly be no more comfortable!).
 

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