It is not. If that one line from the compressor to the center block is not hooked up, there is no air going to the system. So any air coming from the line connected to he center block will be either residual gallery pressure, blows off when disconnecting, or if the system is trying to operate you will have strut or reservoir (both at times) dumping out.

So normally what happens if you request a change in height is the compressor starts and for just a short second or so that is the only thing happening because it wants to build up some gallery pressure. If a strut were to open right away, then it would cause a slight drop in height as the higher pressure of the strut dumped into a near empty gallery. So the compressor runs and get that gallery pressure built up - very, very quickly. Then the strut or struts that need air open up at the valve block. At the same moment the reservoir will open to make the truck rise faster than on compressor along. In theory the reservoir holds enough air for one complete height change and then a little extra. And like I said earlier, the compressor will then keep running for a bit even once height is reached to resupply the reservoir.

 

Pulled center block, no observable damage to any part of it, o-rings all in place.
Pulled compressor, hooked up to 12v power source (almost fried my narrow gauge test leads like an idiot), ran perfectly normal for longer than it was in the vehicle with no overheating. Sustained PSI (cant measure) from the blue port, suction from intake port, but no airflow from exhaust port. Two things come to mind:
1 - Why would there be airflow from the exhaust port when it is not hooked up to the vehicle and there's nothing to move air into the compressor unit?
2 - Some air should be coming out of it because it's an open hole in a compressed air loop. Right?

 

There should be no air flow from exhaust port when in operation unless the blow by tripped which can only happen at high PSI, which means it would have to be hooked up and building pressure. But I am confused by what you wrote. You say there is no airflow, then you ask why there would be? The larger compressor connections, in and out, are just pipes going to a muffler and air intake source inside the cabin. They do not need to be hooked up for operation.

 

I wasn't sure about that part of the airflow path, but you cleared it up.
I made test leads out of larger gauge wire and got even more pressure out of the compressor, sounded normal (not struggling or loud), ran for about 4 minutes before I decided I didn't need to run it anymore. Seems to cut out at around the 2.5 minute mark when on the truck.
I pulled the cover off the exhaust plunger and found it to be very difficult to move. Got it to move, closed everything back up, inspected the piston as best I could without taking the plate off, nothing seems worn.
Everything is back together now, have yet to run the truck because it started pouring rain and it's not in a garage.

 

Got everything back together, started it, compressor ran happily for about 30 seconds then shut off. It did not slowly die out, it just cut out. Same error for "pressure does not increase fast enough" as before. Cleared and watched PSI on computer; increased from 14.5 to 16.1 PSI and then stops. So not reaching anywhere near the pressure I had before. Checked all connections with soapy water, eyes and ears; no apparent leaks. Pressure drops as soon as compressor shuts off.
My logic tells me that, somehow in partially disassembling the compressor, I broke the seal and did not properly reseal it. But then again my logic hasn't really worked out so well on this vehicle.

 

Yeah, sounds like you are leaking really badly. If you can insert a piece of sacrificial tubing into the dryer and pinch it off, you can try to listen to the compressor and hear if it strains to reach max PSI and then blow out the exhaust. Guessing it will not. How far apart did you take it exactly?

 

I do have some sacrificial tubing. Not sure if I have a good way to block it off to max PSI but it's worth a give'r. You're suggesting this installed or out of vehicle?

 

Use a vice-grip to clamp it flat. Does not matter where you run it, just want to see if it can build pressure just to 100% rule out anything else.

 

Clamped it, ran it. Runs for about 10 seconds then cuts off with the same C1A20-64. Then I realized that if I run it in the truck, of course it's going to do do that because the system sees it as no pressure increase and thinks it's increasing too slowly. My GAP tool is in CA, and I'm in MI (long story) so I don't havea great way to force it to run in vehicle (not crazy about using a jumper at the fuse box) and no way to monitor PSI out of the vehicle.
This is with the sacrificial tubing plugged into the outflow (blue) port on the compressor.

 

Ah yeah… ope! LOL