XM Air con pump

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Doc
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XM Air con pump

Post by Doc »

Any air-con experts out there?
Just want to know how easy is it to spin the freewheel clutch on an air-con pump with the air con switched off?
The reason I ask is that my 2.1 XM (manual) seems to be drinking diesel like its going out of fashion![:(] I have checked for sticking brake calipers and handbrake adjustment and all is fine. Car is regularly used on long motorway trips at under 80 mph and I am not lugging a roofrack or junk in the boot either.
Before problem, I was getting around 43mpg but now only getting low thirties. I am begining to suspect aircon pump is not switching out or is binding. With pump off should the plate on the end of the pulley remain stationary or does it spin when engaged.
Could the drop in economy be caused by a malfunctioning EGR valve/control unit?
Thanks in advance [:)]
Doc
NiSk
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Post by NiSk »

A malfunctioning EGR valve will give you BETTER economy! The end plate of the compressor should NOT rotate when the A/C is OFF. The A/C is OFF when the * switch is pressed IN and the yellow lamp lights.
Check that your brakes arn't binding - the parking brake wires often rust and hod the pads on - thus converting your mileage into heat!
//NiSk
Dave Burns
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Post by Dave Burns »

If you suspect the magnetic clutch is dragging, take the drive belt off and see how freely its pulley spins on the compressor shaft, turning the end plate will turn the whole compressor and they put up some resistance.
Dave
Doc
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Post by Doc »

Thanks gents. I have checked the handbrake cables and adjustment and it all works as it should. I have also spent the last few hours checking air con free wheel when aircon is off and it also works okay. I will now disconnect the EGR unit to see if economy improves.
I will keep you posted as to what happens.
Doc
alan s
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Post by alan s »

If you suspect the air/con is operating when the switch is off, why not just turn the internal fan on & see if cold air comes out?
In any case, it shouldn't have that big an effect on the MPG. I had a BX 16Trs that did 7.3L/100klms with air/con & 7.2L/100 klms without.
If the compressor is activating & is seizing or something similar, as Dave suggested, disconnect the belt but I think a clogged air cleaner element or something similar could be your culprit.
Alan S
Doc
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Post by Doc »

Checked everything over (and I mean EVERYTHING) at the weekend. Aircon clutch IS dragging. As it has never been that effective - even when recharged, I will disconnect it. Have also disconnected EGR unit to see if that makes a difference. I change oil and filters regularly so I know the air filter is clean. However after hearing on the news this morning that fuel is going to hit over 90 pence a litre! (and may hit £1 a litre!) I'm going to get rid of the XM as I cannot justify smoking around in a ton and a half of Citroen to commute a round trip of 76 miles. Yes it is comfortable and feels like a limousine to drive but I have to pay for my own diesel.
I will be on the look out for a ZX diesel in the very near future. Or a good supply of used cooking oil...
Doc
tomsheppard
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Post by tomsheppard »

Expensive fuel makes Dubwya rich and forms a good basis for starting wars.
Its an ill wind though if it makes XMs cheaper.
Doc
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Post by Doc »

Decided to hold off selling XM so I can carry out final fuel economy test using daily commute from just outside Cambridge to Stansted Airport (round trip 76 miles) I filled up this morning at Tesco, Bar Hill as their pump prices haven't changed...yet. 77 litres - £65 ouch! I generally keep car at around 75-80mph (which makes parking real interesting) so if I can get over 38mpg I will be happy. I will miss the aircon but using it saps 15-20hp and drops mpg down to very low thirties.
Doc
Guru Meditation
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Post by Guru Meditation »

Jeez that's beserk! Even if it were a bit knackered, how could it soak up 20 brake? A normal aircon compressor will sap something like 1hp or maybe a little bit more. If it were absorbing 20hp it would be getting so hot it would probably blow up or summat? But then again if you have proved it is the cause of the MPG drop then you can't argue with the facts-just seems odd!
NiSk
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Post by NiSk »

An A/C compressor soaks up more like 5-7 hp! That's why most TD12 owners turn it off when overtaking! It makes a big difference at the low end of the power band.
//NiSk
Doc
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Post by Doc »

It was an aircon specialist who told me that a typical aircon compressor in use saps between 15-20 hp. Top Gear mentioned air con and consumption after Clarkson did an economy run from London to Edinburgh in an Audi V8 diesel. No aircon, no cabin fan or radio on. All on one tank of DERV (18gallons)
The other thing to remember is the extra load placed on the alternator/engine when the extra cooling fans come on with the aircon. Hence the 15-20hp deficit.
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