[Jerry]

I'm going to put a better picture and you can see how the air comes out of this black looking filter with holes that seem to be designed to release air.  My coach seems to hold air, my compressor does not kick on.  The air issue is when I push the compressor button on the dash and it runs the air compressor in the front of the coach without stopping.  I think the switch overrides everything and turns the front air compressor on.  The brake pressure is over 100 and then the supply air gauge goes to 70, the air starts flowing out of this black oil filter looking air release system.  Does anyone know what this air release canister is and how it should work? Please look at the picture attached.

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Sorry, old picture.  This is a better picture of the engine battary bay and view of this black air release canister.