How much does A/C "cost"?

[mike.]

Same here, it was never off on my MK5 GTI in five years and has been on so far in the MK6..

[Keithuk]

Well I was cruising up the M6 last summer at around 70mph it showed 57mpg and I thought its getting warm so I put the air con on and watched the mpg. It slowly dropped to 52mpg while I cooled off. I switched it off and it crept back up to 57mpg again. I thought is that a one off so I put it back on and it dropped 5mpg again.

Air con does take depending on the car and system around 5bhp of the engine to drive the compressor. The same goes for the alternator so the more electrical gear you have switched on the more the alternator is working.

Now another thing I hated about mine is if the turn the blower on the screen to demist this damp weather its puts the air con on. Now I now air con dries the air but I don't want it on everytime I press the screen button. If I want air cone I press the bleeding button. The same goes for the recirculation button that puts the air con on as well.

I shall have to look in VCDS if there are any settings I can switch over? 

[dubber36]

My journey in to work today was slow. Super slow. So, while dawdling along the A14, I decided to reset the consumption and see what MPG I get in my GTD with and then without the A/C on.

Without the A/C, I managed to get over 71 mpg over 15 miles. OK, this was at about 55 mph, but still a good number.

With the A/C on, it dropped to about 69 mpg. So, does A/C only cost about 2 mpg in winter (probably more in summer) or should I have seen it "cost" me more?

For the record, I had the temp on 19 deg, low auto.

Did you reset the trip and do the second 15 mile test with the air con on? Even if you did, over such a short distance, the slightest of gradient could have made the 2mpg difference to your average consumption.

On a journey of around 18miles I do quite often, starting from cold, I can average nearly 50mpg on the way there. On the return journey with a warm engine and the same driving style, the average is between 46-47mpg. I'm sure this is down to the journey home being uphill, albeit unnoticable.

[p3asa]

Wow 71mpg that is fantastic. Take it you were just tickling the accelerator most of the way.
I don't think I have ever managed over 54mpg and that's on a lowly 140TD

[Keithuk]

Wow 71mpg that is fantastic. Take it you were just tickling the accelerator most of the way.

Yes I thought that as well?

[dubber36]

71 mpg should be easily achievable if you reset the trip when you are moving and the car is up to temperature. It's not taking into account starting the journey when you will be doing an mpg in the 20's which when added to the 70 odd mpg when warm and cruising will give a realistic average of 50ish.

I did the op's test in my V6 TDI Passat which normally averages 40mpg, and got 68mpg over a distance of 8 miles.

[branchespark]

I know that it is not a fair MPG - that was not really the point. I had to do the test at temp, as I did not want the MPG to vary - other than with / without the a/c and fans.

Normal day I get 55 mpg, unless I am in play mode and I struggle to get 30 mpg!

[Keithuk]

I only reset memory 2 when I fill up. I can only get low 40's mind you 70% of my journeys are local trips. The maximum I've ever seen in memory 1 is 63mpg and that was creeping around 'A' roads at around 50mph. Why do they bother to show actual readings? You put your foot down and it drops to 22mpg you back right off and it peaks out at 200mpg that neither use nor ornament.

[Hartside]

You diesel boys need to get out a bit more  Buy a petrol and don't even think about fuel consumption 

[am1w]

You diesel boys need to get out a bit more  Buy a petrol and don't even think about fuel consumption 

I suppose the only numbers they have which are greater in comparison to their petrol equivalents are their kerb weight, purchase cost* and fuel economy ......... Oh, and the noise.

*GTD is not quite the performance equivalent of the GTI.