Xantia Aircon Compressor.. how much load ?

KevMayer · Post by **KevMayer** » 14 Sep 2003, 22:36

Does anyone know roughly how much load an aircon compressor takes. I have one on my Xantia 1.9 TurboD and when it cuts in, I don't feel much difference in performance. In fact, when I tow a trailer full of rubbish/soil/bricks so there is quite a load on, the engine seems to run better.
Could my ECU be compensating and adjusting the timing of my Bosch pump to give me more power ? If so, do you think I could tweak something so my pump gives me more power when there's no load on ?
My pump is a Bosch AS3. Throttle position sensor detects engine load when combined with engine speed signal from the flywheel.. at least I think that's what happens.
What do you think ?
Cheers, Kev

andycarter · Post by **andycarter** » 14 Sep 2003, 23:44

On mine there is a small increase in load and the engine rpm drops slightly a few seconds after hitting the a/c button.
No noticable difference to acceleration in my opinion although I haven't tried a top speed comparison.
Not sure what you mean about the engine running better when towing [?]
Andy

jeremy · Post by **jeremy** » 14 Sep 2003, 23:55

many years ago I had a 4.2 litre series 3 Jaguar XJ6 which had a mighty 205 bhp engine and produced massive torque, 95% of which was available at 1500 rpm. My car had air conditioning (and was automatic) and I could feel the system cutting in. I suppose it used a hp or 2 to drive the compressor, and when it cut in it seemed as though the throttle pedal kicked back slightly. This clearly was not the case as there was no mechanism for it to do so.
The reason I could feel it cutting in was that if the car was running light at a steady speed it was probably only producing 30 hp or so, and so subtracting the odd hp or 2 upset the equilibrium that had been attained. Acceleration didn't seem to be affected nor did anything else but I suppose the fuel bill was a bit higher when the system was operating.
So the answer to your question is yes you probably will notice it cut in, the management system probably compensates to prevent stalling at idle (mechanical pumps will do this as well as they are governed.
jeremy

David Goddard · Post by **David Goddard** » 15 Sep 2003, 01:58

They ised to say that a/c took about 10% of the available HP. Presumably, that was related to a small engine. I would guess the compressor draws about 7 or 8 bhp. To this need to be added the power used by the "heater" fan, plus engine cooling fan (two run on my car). So the toatl could be 10 bhp or more.
The a/c load is very noticable on a small engined Saxo / Corsa or similar. Up-hill pulling power is noticably affected. You soon get the habit of turning the a/c off for a few minutes to get more go!

algieuk · Post by **algieuk** » 15 Sep 2003, 02:21

Air conditioning can tak a LOT of power. Used to have a 3 litre volvo with cruise control. When the AC kicked in it would drop the speed by 5mph at 70 before the cruise control could recover. It is quite common to have a solenoid or suchlike to open the throttle more when the AC compressor is running. If this was over-compensating this woudl account for the car seeming to run better. In fact it is only that same as applying more boot.
Reports show that AC can increase fuel consumption by up to 20%, but this would vary from vehicle to vehicle
http://oee.nrcan.gc.ca/vehicles/tips/ti ... rintView=Y

Dave Burns · Post by **Dave Burns** » 15 Sep 2003, 03:15

I have to go down several steep hills going to and from my place of work, with the aircon on I don't have to use anything like the amount of brakes that I do without it, and since having the system recharged it seems even more so.
I'd agree with David Goddard that 10bhp sounds about right.
Dave

KevMayer · Post by **KevMayer** » 15 Sep 2003, 03:26

Thanks for the replies. This is a great forum.
In reply to AndyCarter... What I feel is that when I tow with some load in the trailer, my diesel engine seems to run better. It sounds better. I hear the turbo whistle and get that burbling sound when I press the accelerator at low revs. It seems to pull nicely, as though the engine has compensated for the increased load and this has somehow moved the performance into a better set of operating characteristics. Maybe its just my car. But because it runs "better" when under load, it makes me suspect that it isn't quite set up correctly for normal/light load conditions. I've tried rotating the throttle position sensor slightly to try to trick the ecu into thinking there is a load on the car. It does seem to run better when I do this. but then when I connect up my trailer, it sounds a bit rough, as though it could be pinking (ie. timing too advanced) so I have restored it to the original setting. Hence, I suspect the aircon load is compensated for and thats why I don't seem to feel it have any effect on performance.
I hope this makes sense, you may need to read it 5 or 6 times ...
Thanks for your interest and replies.
Cheers, Kev

alan s · Post by **alan s** » 15 Sep 2003, 04:06

I don't know what kind of system they use on models Xantia upwards, but when I had the 16Trs I did a couple of tests on fuel consumption with & without air/con on.
It did 7.2L/100klms without & 7.3L/100klms with it on. Power was almost unchanged on open road cruising however it did make life interesting around town particularly as you took off at an intersection. This could be explained by the head pressure of the compressor being lower when cruising due to the air passing over the condensor hence reducing teh load.
FWIW, I knew one guy who once fitted air/con to a GS and found power loss a big problem so he fitted a "make & break" switch to his accellerator so that whenever he hit it hard, it cut power to the air/con clutch which automatically restored as soon as he backed off.
Alan S

Post by **RichardW** » 15 Sep 2003, 12:55

Nothing to do with ari-con, but about 20 years ago I remeber my Dad had an Ami 8 and the regulator went on the alternator - drive along and the lights would get brighter and the wipers faster, forcing a stop to disconnect the alternator. He got bored of this after a while, so fitted a switch instead (not wanting to splash out on a regulator that would have cost more than the car was worth!) - he used to turn off while going uphill as it made a noticeable difference to the performance!
I believe most modern ECU controlled cars are programmed to back off the air con under heavy acceleration to reduce the load on the engine.
Richard

kafkaian · Post by **kafkaian** » 15 Sep 2003, 13:21

This forum has yet again answered some of my own queries on A/C versus performance. Particulary during the hot weather this summer in the UK and after about an hour's driving, the engine got distinctly ropey and unresponsive in heavy traffic. The solution? Turn it off at strategic times and everything returned to mormal: Less pinking and more power. I have to say though that on my Xantia (see signature) fuel consumption is awful when the A/C is on leaving me to turn it on for ten minutes a month (for longevity), when it's above 27 to 30C outside or when I have no choice driving through dodgy parts of Birmingham that would otherwise allow me the pleasure of the windows down.

stuartb · Post by **stuartb** » 15 Sep 2003, 13:50

Some years ago, I had a Rover 827 Sterling automatic with A/C. If you used "kick down", the ECU turned the A/C off to get maximum power until you lifted your foot off a bit. I think this is quite common, but it does illustrate the fact the the A/C does take a noticeable amount of power!
Hope this helps.
Stuart
'93 Xantia 1.9TD VSX - 120000 miles.

allmond · Post by **allmond** » 16 Sep 2003, 01:57

My BX GTi had aircon. If you were going along on a steady throttle and turned the aircon on and off, boy could you feel the difference! It plainly took a lot of power, and I only used it when I really needed it.
My Xantia, by comparison, (1998 2.0 petrol Exclusive) is completely different. I have tried all sorts of tricks to try and notice any difference when switching the aircon on and off, but can't notice any effect on performance or fuel consumption. I now leave it on all the time, summer and winter (it dries the air coming in very effectively) and motor in cool comfort all the time.
Oh, by the way, yes it does work!!
Jamie