ALC problem: no pressure relief

Hello folks,
I´m new here. My name is Wolfgang, I´m from Germany, and I just recently imported a 96 Roadmaster Estate (bought from Fred Lesinski). What a great car! There´s one problem, however: While the ALC system works just fine (no air leaks, compressor works as it should), the rear of the car does not go DOWN anymore. Due to the fact that the compressor runs for a couple of seconds a each time you start the engine, there´s pressure building up. After a while, the back gets higher and higher, the shocks get stiffer and stiffer; the car´s tail almost jumps. But I have to releif pressure manually by taking of an air line. Any clues what could be faulty? Thanks!

Hello Wolfgang, and welcome to AF! The level switch under rear suspension should stop the compressor when designed ride height has been achieved. Check the switch lever & linkage, to see if they are free to move and operational. In addition, make sure to check the switch terminal contacts and finally the switch.

Mechanically, the level switch is fine. I suppose this limits the possible causes to the wiring or the pressure relief valve in the compressor unit. How can I find the fault? Which wires would I have to use in order to simulate a "too high" condition for the valve?

Hi Wolfgang,
I think the best way to simulate the real life is to disconnect the linkage and move the lever by Yourself. By moving it up and down You should hear the compressor go on and the pressure relief valve open alternately. One possible problem (that I have on my -95 RMW) is that the relief valve is stuck. I have bigger problems with my RM so I haven´t dug any deeper in the matter, but You can quite easily remove the compressor from it´s place behind the front bumper on the drivers side. You just remove the plastic cover from under the car and You see the compressor. I tried to get my relief valve unstuck but I´ve given up for the moment and just disconnected the system. Please post any success or discoverys You have, it will help me and others!
BTW, I´ve opened the lever and seen electronics inside so I´m not sure if You could short any wires directly to simulate the levers function, it may be a bit more elaborate than that.
Here´s some pics of the levelswitch:
http://grandis.lloyd-willner.se/css/buickstuff/als-switch-assembled.jpg

http://grandis.lloyd-willner.se/css/buickstuff/als-switch-inside.jpg
Hope this helps, even if the thread is getting a bit old :)

Hello Benny, thanks for your answer and for taking the time to illustrate it very well, too - that surely helps a lot! I´ve not takled the issue yet, so your help is not too lae and much appreciated. From visual inspection, my switch should be fine, so I suppose it´s a stuck relief valve. I will check this first. Thanks again! Wolfgang

Hi again Wolfgang,
I´ve just fixed the problem on my RMW -95. It wasn´t the relief valve after all, it is well tucked in away from weather and dirt so it checked out good. However I started to wonder about the cylinder that is connected to the compressor/relief valve at one end and to the thin airline that goes to the shocks at the other end. I think it´s some kind of "air speed damper" so the vehicle doesn´t drop/rise too quickly when on the road. It seems to contain some granulate, like sand or something. Anyway I sprayed a little teflon lubricant into it at both ends and after that I could, slowly, blow air in both directions (which I couldn´t before). Back on the vehicle I just put the winter wheels on the back to lower it and the compressor started fine. When I took the wheels off the rear gate it started to let air out after about 20 secs - IT WORKS :)
It may be the problem with Your one as well.
/Benny

Hello Benny,

that´s great news - thanks for sharing it! I´ll give it a try next weekend. Didn´t have a chance to deal with the system yet, but your positive experience encourages me to get going.

Regards,
Wolfgang