Pulled the compressor out, hooked it up to 12v, with output blocked off. Immediately got airflow out the infeed. Opened the output, no outflow, and no change to air coming in the infeed.
Immeadiately checked that leads were pos/pos and neg/neg. Nothing wrong there.
Started disassembling the compressor to see what I could see.
The metal "membrane" above the piston was reversed. I must have flipped it around when I reassembled it.
Hooked compressor up to 12v with input tube closed off. Runs for about five seconds then begins to slow and die, took about one second to go from running to motor boat no go.
I'm going to see if the local parts store has anything I could use to measure PSI from the pump. Probably wouldn't be a bad idea to have more air testing tools anyways, given that I have a vehicle that has a lot of air equipment.

 

Well, more progress is good progress. A fuel gauge could probably be fitted to work, just not sure the max PSI on those things. But then you have a fuel pressure gauge on hand.

 

Ok, made my own guage with some hardware store and Oreilys finds. Compresser begins to slow at around 80psi, dies at around 100psi. So that gives me somewhere to start.
Compressor clearly needs to be rebuilt or replaced. Hoping for a rebuild. Takes about a week for anything to get here from anywhere. Any thoughts on what part of the compressor could be failing? I'll try to get a video of it running and quitting.
It also seems that there is a leak somwhere in the system, but seeing as I wasn't having any signs of it before this all started, I'm guessing it was small. Could be larger now, but I can't really find that out until I can get the compressor putting out the correct amount of air.

 

Dont rule out a power supply issue. As pressure builds, it starts to eat up amps. But assuming that is good, then it would seem that it has a performance issue. Typically it is a worn piston/cylinder. Or in particular, the piston "ring" which wears and also wears the cylinder.

Of note! Do not ever lubricate any part of the compressor. It is a dry compressor and any lubricant can gum it up and kill it fast. My dumb *** thought it would be a good idea to use just a little silicone lubricant for the piston. Nope. Dumb. Gummed it up and it did not last long.

 

Ha. When I pulled the old one apart, it was filthy with lube, seemingly silicone. I wonder if someone had tried to rebuild it, or if it came like that... would explain a lot.
Seeing as it cuts out around the same PSI in the truck and on the 12v supply, I'd think that it wouldn't be a power supply issue, but wouldn't rule out electrical in the compressor itself?

 

Went back out and retaped the fittings on the gauge I made. Comes up to 120psi and cuts out. Left the gauge on the compressor and sprayed down with soapy water. Minimal bubbling around the air dryer body/cap seam, but very minimal. Lost about 1psi/minute on the gauge. The motor on the compressor sounds like it doesn't have the power to keep going, and if it were the piston/ring/cylinder not sealing it seems like it would just keep running until it overheated. Does that line of thinking make sense?

 

Well dont discount leaks, think hole in straw. But yeah, if it can not build up pressure then it sounds more like the motor itself is having issues. It should be able to reach 200psi minimum. I think the original spec was 238 or about but LR lowered it with a software update. So either way, 120 is pretty low.

 

I had a Arnott in one of my LR3's and the 12V high amp motor connector melted, was causing strange issues like what you are describing. That one drove me nuts because as measured electrically everything was fine and not until I actually examined the connector did I find it. It would pass low current DVM tests with no indication of a problem.
Also mentioned you're in MI, don't know if you are close to Petoskey?

 

Interesting... was that the Hitachi or AMK style?
I am near Petosky... I'm in the south arm of Charlevoix area for another few weeks.

 

Arnott only makes the AMK "style".