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Discussion Starter #1
Hi All,

Apologies if the answer is here somewhere but I haven't been able to find it yet. Anyway, I've been working on getting my air suspension working properly again. Currently, it appears that the compressor won't shut off, I think from the high pressure switch? Here's the list of events so far.

Warning: Running Gear and then eventually Fault: Running gear.
1. I started looking at the system and noticed high duty cycle and related VCDS errors.
2. Looking at the compressor, I found that the brown tire extension had blown off and had a hole in it. During this time, I ended up replacing the compressor piston head, ring, and refreshed the dryer material as well. The head needed replaced as the threads to the elbow that connects to the tire pressure outlet were stripped. The fixed brown hose, was stretched and ended up getting a new hole created from hot compressor, I think.
3. brought new brown output hose for tire outlet. Cleared the alarms, and the air compressor started, unit shows pressure building in VCDS, while I had everything apart the compressor seemed to stop. I put everything back together and test out. This time the compressor seems to not stop, have to pull the connector to the compressor by the valve block to kill the compressor running.
4. I check the relay (373) D3 behind the dash, and confirms that it is triggering using the 12v across the terminals, continuity starts and stops as expected from 12v current.
5. I plug everything back in and test again. The compressor builds up pressure until about 18.3 or 18.6 bar and then the output that goes to the suspension blows out of the compressor! Additionally, I can't seem to get it to stay in now. Needs a new connection? How to fix?
6. I pull the solenoid to see if it is stuck, but everything seems to be normal, I plan to test with 12V to see if it triggers.

Currently, I am thinking that there is a trigger that should occur, probably somewhere around 18bar?, that causes the solenoid to trigger and the compressor to turn off. However, I have no idea where it would be if it exists. Additionally, I'm not sure what my next steps would be at this point. Any help would be greatly appreciated at this time.

Thanks everyone for your input.
 

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VW recommends replacing the compressor relay whenever replacing the compressor. I am wondering if your relay is stuck closed. Due to arcing, the tabs inside can weld themselves closed, unfortunately.

Does VCDS show the compressor turned off when it continues to run? If so, then your relay could be fused together. Since you're readying 18 bar of pressure, the pressure sensor appears to be working. AFAIK, there is no emergency blow off valve. Aside from one of the air lines, as you have found out.
:- /


As for the hose that popped out, make sure the end is in good shape and free of burrs. It must go in as far as it can. Make sure the collar is able to move around it. When you insert the hose, the collar moves "in" and when the collar moves "out", it grabs the hose and secures it. The harder the pressure to remove the hose, the harder the collar is supposed to grab the hose. If the collar can't move back out, it may not be grabbing the hose.
 

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To reiterate what FSJ said. Anytime you replace something that relies on a relay, or contactor to supply it power you should replace said relay, or contactor, as well. Even if the contacts are not fused often they can build up pitting. Which will also cause them to fail.

And, someone might be able to provide better input. But, something sensitive like smaller relays, and what not, I would lean heavily towards OEM.


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Discussion Starter #4
Thanks guys. However, I have a question regarding the relay.

When I tested the relay, I removed it, placed 12 V across terminals 85 and 86(I believe). I verified that I heard the click and the connections between terminal 30 and 87 when from infinite resistance to continuity. Additionally, once I removed the 12 V, the continuity stopped and returned to an infinite resistance.

So, could the relay still be failing with this test result?

Also, how far does the collar need to move out? a few mm? more? And if it isn't moving out enough, is there a way to replace it?
 

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Discussion Starter #6
I've just been relying on the normal start up process. How would I go about turning the compressor on? I do have VCDS but not sure of the process.

I have noticed that on the measured block the compressor relay will switch to off and the compressor will continue to run.
 

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Relay is cheap. Start there as they are known to fail.

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Discussion Starter #9
So...I got a new relay, and it appears that was the issue. Thanks for the advice guys. Mine was 8D091253A, but I believe that 4H0951253A is the same relay.

As I mentioned, when I tested it out of the system, the relay was switching on and off as expected based on voltage, indicating a working relay. However, I took off the cover once it was replaced and manually made the connection. I noticed that sometimes, it appeared to stick closed a bit. I assume that this was enough for the current to hold the relay closed, even when the switching voltage was removed. I'll have to remember that in the future!

Now, hopefully once I get the replacement output plastic, my T-reg will be good to go. Thanks again everyone for the help.
 
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