Invisible air leak

The only other thing I could think of is if the one way check valves at the inlet of the primary and secondary tanks have failed/been removed and that is causing air to bleed back into the wet tank and out through the intake of your compressor (which it shouldn't do). Depending on how your compressor inlet is configured it could be coming out through your truck's air filter(s), which would likely muffle the sound of the escaping air. Very unlikely this is it but its really all I've got.

 

I dont know about being able to hear an air leak. I lost all my air once in a rest area. Heard the line pop and all air was gone in 20 seconds. Could not find it to save my life. Ended up having a service truck come out and ran his air supply of 150 lbs to find it. Without all the unanswered questions it sounds like the major air line supply has s break in it to not hear the as I'd leak. Belive it or not but try listening sometime when you have the supply line off the air comp. You almost can't hear air coming out when running just a pulse of air when you hold your hand over the opening. He needs to do all the steps recommend by everyone. Shop air should help.

 

Definitely. The thing that gets me is from my understanding so far the truck builds air just fine but when he shuts it off it starts losing it over 5-10 minutes. A guy should be able to hear something if that's the case.

 

Oh I didn't see that post. Yeah if it is building air then leaks off after shutting down, then yeah should be able to hear it.

 

Brand new doesn't mean it's working properly. I'm my experience, a brand new dryer is more often than not replaced as a guess because someone cannot find the cause of a problem. I honestly think you need to find a mechanic other than what you've been using.

I'll try one last time:
1. Does it purge at cut-out?
2. Does it hold air pressure steady at idle?
3. Pump the brakes to cut in pressure, then let it build back up. How long does it take to go from 100 to 120?
4. Did the air dryer purge again once it hit cut out pressure?
5. Again, did you verify that the tank are in fact totally empty by pulling the drain cord on every tank?
6. How did this problem start? All at once? Slowly get worse over time?
7. If it happened all at once, was any work done at the time this started?

 

In addition to the above;
I would disconnect the 2 airlines to the Trailer build up air pressure & see If It leaks down. This will isolate the problem to either your truck or trailer....