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Aircon and fuel consumption - Ian Cook
There have been a few posts recently about the affect of airon on fuel consumption. I've recently been running with the aircon permanently on, and the following are the results of brim-to-brim tests under the same driving condiditons (approximately 1200 miles in each test, 2 fills).

Aircon OFF: 49.73 mpg (July 2001)
Aircon ON: 49.83 mpg (August 2001)

The car is a Xantia HDi (110)

My conclusion: do as HJ advises and leave it permanently switched on.
Re: Aircon and fuel consumption - Michael
Ian, I think your results confirm my thoughts that, assuming you have an adequately powered engine, the effect on fuel consumption, of running the air con permanently, is negligible. The problem, I suspect, is when runing the air con on a small engined car (particularly on a low torque petrol engine) where the impact may be more significant. Having said that, I am equally convinced that avoiding the cost of repairs to the air con unit out weighs the slightly better fuel consumption. So, I agree, leave the air con on.
Re: Aircon and fuel consumption - David Woollard

Decent figures regardless, you appear to get another 6mpg over our 1.9TD in normal use at 43.98. It takes some care but ours will go up to 47mpg on a better tankful.

I wonder what towing does to it, 10mpg loss or more?? On that subject you commented, good natured as ever, on my dig at caravans. Actually my comments were an attempt (failed) at ironic humour. You should know I very firmly think the road is for everyone, up to the rest of us to drive round the hazards with a cool head and cheerful disposition.

Re: Aircon and fuel consumption - Ian Cook
No offence taken, David.

Regarding mpg with the HDi. It's difficult to get less than 49mpg with this car. My previous 94 TD Xantia consistently did 45mpg. I know because I always brim fill and have all the records for my cars back to 1988 (petrol and diesel) - it's been little hobby of mine.

Towing a caravan with the HDi I get between 30 and 31mpg. I work on a rule of thumb of about 60 - 65% of the solo mpg and this has been fairly consistent over the years. Mind you, it's increasingly difficult to tow on the motorways at a steady 60 because of being squeezed by trucks, and I'm not allowed in the outside lane. It's not their fault, there are just more of them these days.

Re: Aircon and fuel consumption - Brian
I recon around 50 mpg on a long run in a Pug 405 turbo diesel and 40 mpg when towing a folding caravan, only approximate figures though.
Re: Aircon and fuel consumption - honest john
The reason for the variation in Citroen fuel consumption readings is the variation in accuracy of the odometers. Of all the cars I have tested over a regular 300 mile journey, Citroens average 320 miles, Fords 310 miles; VWs and Mercs 300 miles.

Xantia mileage recorders. - David Woollard
Oh dear. Didn't want to go public on this aspect of our claimed fuel consumption figures but.....

It is true that a Xantia is likely to revise you estimate of distances travelled. Funny how those previous 105 mile journeys go up to 113 miles, I thought it was just a wider cornering line!

Re: Aircon and fuel consumption - Ian Cook
Yes, odometers can vary. The point of the thread, though, was to give information on comparitive consumption with and without aircon.

I know that the HDi is better than the TD Xantia and ZX TD on fuel because I know how much fuel I use for regular journeys. I think that Xantia odometer is about 2% faster than the ZX.
Aircon and fuel consumption - David Lacey
Good Point HJ!
Re: Aircon and fuel consumption - chris j catton
Whilst newer cars may experience little consumption degradation through use of air-conditioning I must point out that when I got my 1987 XJS (5.3L V12) there was a significant amount in the order of 10%, I could feel the change in roadspeed when the compressor kicked in. NB. It was checked as being in full working order.

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