What's fuel economy like with air con on?

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Jaf
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What's fuel economy like with air con on?

Post by Jaf »

Hi guys. My fuel economy is normally very good (1000kms on a tank; it's very, very hilly round here). I've had the air con fixed after 4 attempts and have been going everywhere with the air con on. It's been wonderful. Problem is I've just filled up and only got 800kms. Now I know that air con is juicy but I'm sure I've read 8%, not 20%?

Cheers, Jaf
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Post by DickieG »

There have been many articles over the years about using/opening what costs X amount so whilst A/C uses fuel so does opening the sunroof/windows using the heater fan etc. 20% does sound very excessive which makes me wonder whether your last fill up was using supermarket fuel which is notoriously poor for mpg.
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Post by Jaf »

Ooh I remember supermarket fuel. Nice and cheap and could get high octane. Living in the mountains of Spain the supermarkets aren't exactly "super". Can't buy towels, glasses, bikes etc. like I remember. Grumble. Big supermarkets and takeaway food are about the only things I miss. Anyway it's not the fuel quality that's the problem. Will have another look for fuel leaks since you reckon 20% is too high. Thanks for confirming it.
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Post by Sl4yer »

The Lexia shows that switching aircon on (at idle) increases injector time from 2.2 or 2.3ms to 2.5ms, so in the order of 10%. I'd expect that to be unnoticeable when on the move, with the engine under load.

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Post by Peter.N. »

It depends how you drive. If like me you drive very carfully and get 50 mpg + you will notice the difference because you are only using a relativly small ammount of the engines total output so a small increase of power demand is much more noticable than if you drive with your foot to the floor, in which case you would hardly notice the difference.

I nearly always use supermarket fuel and get 40 - 50+ mpg from my XMs and 50 - 60+ mpg from my 406 Hdi.

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Post by Jaf »

Interesting James. Actually switching the air con on does diminish the power quite a bit, especially on the hills. It feels like the car is twice as heavy and I just can't make it up the hills without going down to a lower gear then normal. I did borrow a car for a day, whilst mine was in the garage, and the power loss seemed to be similar though I didn't have the other car long enough to see what the fuel consumption was like.
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Re: What's fuel economy like with air con on?

Post by Jaf »

Hi guys. Now that the weather is cooler I've not had the air con on much. I've got 930kms out of the tank which is a huge improvement on 800 and I reckon the next tank with no air con at all I'll be back to 1000kms. Nothing has changed on the car, haven't done any servicing or anything. There is a leak on the air con compressor, takes 6 weeks to leak the gas away, so I guess the compressor will be working harder than normal. I have ordered a tin of air con sealant, I wouldn't normally use sealant but the compressor is 500euros. Apart from the leaky compressor is there anything I can service that would help it not use so much fuel?

Thanks, Jaf
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Re: What's fuel economy like with air con on?

Post by xantia_v6 »

One thing to remember is that the power required by the A/C compressor goes up with the temperature of the condenser, and again with the amount of heat being removed from the car, so will use a lot more fuel in Spain than in the UK.
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Post by addo »

That's getting closer to the mark, I reckon. A leaky compressor is wasting engine power and more importantly heating the gas excessively.

Compressors seem to usually leak from the front seal; to repair this is not too hard for a techie with the Sanden tools. Certainly not a 500 Euro job even with degas, regas and new drier. As oil is lost, topping this up is important...
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Re: What's fuel economy like with air con on?

Post by Gibbo2286 »

Wind tunnel tests suggest that air con generally adds 8% to fuel consumption, tests done at the same time suggest that driving with the windows open causes pretty well the same increase in fuel consumption.
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Re:

Post by Jaf »

addo wrote:That's getting closer to the mark, I reckon. A leaky compressor is wasting engine power and more importantly heating the gas excessively.

Compressors seem to usually leak from the front seal; to repair this is not too hard for a techie with the Sanden tools. Certainly not a 500 Euro job even with degas, regas and new drier. As oil is lost, topping this up is important...
This summer was actually quite pleasant. The highest it got to was 40 and the norm was about 34. Last couple of years, without the air con I just haven't gone out apart from food shopping! It was bliss having air con even though I had to have it re-gassed twice.

The 500euros quoted was for a new compressor. No disrespect to the Spanish round here in the countryside but they don't seem to know how to repair air con. It took 4 re-gas and checks using 4 different garages, including Citroen, to find the leak. Not only that but I would only have air con for at best a week and at worst 20 mins after the re-gas. The last guy, who makes the air con last 6 weeks and found the leak, is German but he says compressors can't be repaired easily. He also mentioned a filter which costs around 200euros. Anyone know what filter that is?

Could I run the car with the compressor off? Could then send it off to Madrid or more probably someone in the UK.

Cheers, Jaf
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Re: What's fuel economy like with air con on?

Post by lexi »

What's fuel economy like with air con on?
No idea...........none of those 2 above features work on mine :shock: :)
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