awdinut

The problem is my compressor runs much of the time while I am driving. Many times when I come to a stop at a light or sign I hear the compressor turn off accompanied by the sound of a 'fooosh' of air....and sometimes I hear that while underway. Its been this way for a year. Two new Audi struts this year. Compressor only puts out 2.5 bar, but when I replaced the valve block (with used one) last week and all 4 corners were down from disconnecting lines, the pump lifted the car to proper height in less than 5 minutes.

Jack Mode off, the car does not lower over night. So if my car is not leaking, why does the compressor run when underway ?!! Its a very unluxurious sound and I am really fed up. The front end collapsed a couple weeks ago, but it turned out to be that the plastic air tube had come out of the brass fitting at the top of one of the struts and I re-attached it.

I have only seen one other thread that talked about having the compressor run while driving and they had the turning off when coming to a stop symptom also; but there was never a resolution posted that I could find....any thoughts appreciated.

Jack88

The pump only runs if the pressure in the system falls. You are losing air somewhere. Also, my pump pumps the bottomed out car up in about a minute, so 5 minutes is excessive.

Richard Meisel

Look in the air inlet line there is a damper of some kind.
when you open it there are two bras discs in there where the air is supposed to run trough the get cloged up over the years so the compressor cant get enough air.

awdinut

and thats why I included the fact that the car doesnt drop at all over night. But in theory you are right...the compressor runs to make-up a deficiency. So the question becomes: what could be happening when I drive the car (that isnt happening when the car sits overnight in Jack Mode) that cause so much air to leak out that the compressor runs almost constantly ?!! OR...what could make the the compressor THINK it has a leak when there is none ?

And of course my 2.5 bar compressor isnt as fast as one in proper working order, but the point was to show it isnt worn out to the point where it wont lift the car and would have to run constantly because it isnt making pressure. If the PDF of R&R instructions for W12 compressor were not 23 pages long i would re-build mine.

Jack88

The difficulty with the W12 compressor is accessing it, I think, but I had thought it wasn't too bad! Anyway, maybe it isn't a strut leaking, there are other components that can leak. There are a number of fittings and there is a reservoir, maybe it's one of those things. I think those can leak without causing a drop in ride height, and if so, then it would lose pressure even when sitting. Does the compressor come on first thing when you start the car?

awdinut

Yes, well, accessing the W12 compressor IS the 23 page difficulty...have you done one, if so I'd like to get some insight. As to a leaky reservoir, its my understanding that the compressor runs only to fill a reservoir when it is less than full.....so when the car is in JACK MODE if there is a leak, is the reservoir keeping the car at height overnight (assuming the leak was not so large as to completely empty the reservoir) or does the JACK MODE shut the reservoirs down also ?

And yes, my compressor runs in the morning when I leave and turns off with a whoosh of air at the stop sign 3 blocks away. And the pattern of stops and whoooshes continues all day.

Jack88

I think the reservoir emptying would not affect ride height in jack mode, the valve block separates the two parts of the system and as long as jack mode is engaged, it will keep them separate.

dvs_dave

awdinut

No leak in bag,,,two new Audi struts with in past year.

As to system wanting more pressure...is there something I am not understanding about the way the system is designed to work ? If the pump brings the car to prescribed height, what does the system care about pressure ? Does it not operate on volume measurement ie. the reservoir needing to be full and the bags full to the point that the car is to height according to the height sensors ?

Also, I dont know how long the compressor can run before thermal shut down, but I should think its at least 5 min ? In the morning when I leave it takes 2-3 minutes to get to the first stop sign; at which time the compressor will always shut off with a whoosh of air when I come to a stop. So at that point the compressor is not doing a thermal cut-off; it has not run long enough. So whats with the shut off at stop sign/lights ? That happens all day long and the intervals are frequently too short for thermal shut down....

ltooz_a6_a8_q7

Looks like everything you replaced already, somethings that cause the pump to turn on is when the valve block see the difference between the tank and the struts more than 3 bar of pressure. The front struts are new, the rear has the extra air reservoirs, I would check all the connections hoses. W12 is heavier than normal A8, the valve block may work harder since the struts do work harder.
Cheers,
Louis