No Air pressure, plz help

Check valve on compressor, or maybe purge valve stuck partially open.

 

You should be able to rev the engine up to around 1,800 rpms and the pressure should build up to 100 or more. Shut the engine off, get out and find the leak. I'm guessing an air bag

 

Take pipe from compressor off and see if it is pumping strong to check compressor.
Is you can get external air/Shop air then plumb it in to the first receiver tank then you can look for leaks all round the truck with the truck not running.
At our shop we have a fitting to plumb in to pipe coming from compressor , this enables us to check everywhere with out the noise of the engine running.

 

The braided line should be a 1 inch wrench size sometimes 1-1/16. I doubt you have a copper hot line being that new of a truck. If you trace the line from compressor it will go directly to air dryer. Just a poor boy method here but if you can hold your thumb over the compressor side with engine at idle the compressor is shot. If it blows your thumb off its ok

 

The main line from the compressor is usually a big braided line, and you will need a big crescent wrench or about a 1 inch open end wrench to loosen the nut. With the engine running, you can feel with your hand if it is pumping air. Try to block it off with your hand, and if it pushes your hand off after a few seconds, you know that your compressor, and your governor, are ok. But if it still wont build air, then you have a major leak downstream. Someone mentioned an air bag, maybe also a maxi pot, or the dryer itself leaking. If there is a major air leak, you should be able to hear it as soon as you shut the truck off. Is it cold where you are? Cold enough to have frozen lines or valves? That is another issue, but one that needs to be considered, if it is cold. Give us some more info and we can help you figure this out.
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He means the solid pipe,not the braided steel line.You need to look around and listen and feel for escaping air.take off some air lines starting from the pipe,if that's what's there at compressor which should feed a line to your air dryer.

 

If you have another steel pipe from egr pipe to compressor,don't take that off it is the air intake for the compressor.