Good questions, not all good answers...

In my case, the key symptom was a long-running and loud compressor. Why would it run longer and louder? Longer if there was a leak somewhere in the system. Louder if the piston rings wore worn. Since none of the corners sagged even after days of sitting, the leak doesn't appear to be there. This lead me back to GL450x164 initial recommendation to look at the reservoir (which is a component of the Arnott compressors). That was stated again in the post above, because after all the conversation, the initial recommendation and diagnosis appears to have been correct. I determined that did, in fact, make the most sense because over the last couple months I had noticed the compressor running longer and longer with time. On trips it would usually run maybe 3 minutes, it was later running 5 minutes and recently ran closer to 6. With all of this in mind, the problem would seem to be getting progressively worse. A small leak in the reservoir could eventually become a larger leak, right?

If you go this route, I would also recommend following GL450x164's advice on ordering from FCP Euro. A little more expensive, but worth it if/when another failure comes along.

We vacation in Maine as often as possible. Sadly we don't live there...but retirement is only a handful of years down the road. We plan to visit Belfast again for a couple weeks later this summer.

 

I guess my question about a leaking reservoir - and admittedly I'm by no means an expert so maybe I'm not thinking this through all the way - is that if there was a leak in a tank, even small, it would never build full pressure as the air is constantly leaking out... meaning the compressor would be running not just for a long time at one go, but there would also, constantly, be extremely short "not running" times. And, after sitting for a few days and all the air leaking out, it would have an extremely long run time upon first start up to fill the system?

Maine, did you ALSO replace the reservoir? If you mentioned that, one way or the other, sorry - I missed it.

Either way, since my compressor is starting to get loud, I know that AT LEAST it is a culprit. Could be more, but definitely at least the compressor.

Yes, I agree with buying from somewhere reputable. I would buy either from Arnott or FCP.

 

Your logic is reasonable on the operation of the compressor with a leak in the reservoir. My rationale (right or wrong) was that through a reasonable process of elimination, that was highly likely to be the culprit of my longer than usual run-times. In addition, much like you, I was troubled by the louder than normal sound of the compressor. Since we are going to start dragging around a 6,000 pound hybrid in a month or two, I didn't want a failure between home and a campground. I would have loved to been able to run some real diagnostics with the Star/Das system, but alas that just isn't in the budget. If I could find a quality used piece or a reasonable alternative, that would be great. Based on the worn piston rings, I guessed it was likely that the compressor was on its way out, so it seemed like a reasonable attempt at a solution that would--at a minimum--happen on my schedule as opposed to a surprise. I checked the air intake hose and replaced the compressor filter as well during the process.

The reservoir is actually a component of the compressor. If you Google any pictures of the Arnott P2594 you'll see the reservoir tank is attached to the bottom of the compressor.

It's a pretty easy job, good luck!

 

I'm right there with you - better to replace it on your own time. Luckily, for me, right now I don't have any trips and I have a second car - so if worse comes to worse, I can just park the GL in the garage. Sounds like you have some fun times ahead of you! Hybrid... for racing?

The reservoir is attached? Hmmm... I did not know that! I had always thought that there was a separate reservoir tank in the back of the vehicle? So it's the black, plastic cylindrical thing with the AMK sticker? I never realized that!

 

OEM reservoir on the pump is plastic. It cracks which requires replacement. I could not find a rebuild kit and had to replace mine with an Arnott one.

 

There is another reservoir under the rear between the mufflers but that is not likely your problem. It's covered with a black plastic shield.

I have had a number of issues with airmatic on my 2008 GL320. Whenever I had an air spring problem it was fine while running the car but would sag after parking. When a rear one was faulty it would lean to one side. When I had a front one fail the whole front would go down. When my front one failed it was strange as the car would never sag after shutting down if I manually raised it and then lowered it again before shutting it off. Turned out the airspring was developing a crack at the fold that would tend to leak only at a certain height and by raising and lowering once if was fine. The rears failed at 6 years and the fronts failed at 9 years.

The most recent was the compressor. In the shop as I write this. Vehicle is 9 1/2 years old. The compressor would take much longer to raise the vehicle to the raised height. It never sagged when parked overnight or while driving, but I did start getting a "malfunction raising" error and a "compressor cooling down" error while driving. I took it in at that point to get diagnosed as I was afraid I would fry the compressor if it was not the problem. Mine was very quiet and hard to hear when the engine was running but when it was raising it was very slow as it struggled. They did a complete check of the system and they said they discovered a leak at the compressor fitting and also the compressor was apparently only developing about 1/3 of the required pressure which makes sense as it was having great difficulty raising the vehicle. I would have got the vehicle back today but after I was testing the raised height before leaving the shop I discovered that even when it reached the manually raised height and the compressor shut off it would start again after about 5-10sec and then would continue to run for a few minutes until I pressed the button again to lower the vehicle. They were going to recalibrate it so tomorrow I should find out what happened. Hopefully all will be ok as it was an expensive visit.

The valve control block is another part that could not be functioning properly. I haven't have that fail yet. I think you really have to take it to someone who can fully diagnose it.

 

Just long enough to raise the strut which has drooped by morning so about 10-15 seconds.

 

Just put a new compressor in.
It raised right the first time or two.
After a bit, shut the car off, and the compressor has been running constant for a while.
Not sure if the relay is stuck or what?