under my front hood we have air coming out of the fitting without the hose, beside the two hoses, anyone know what it is?

That might a vacuum generator for the dash heater/ ac controls.... The black round ball is the accumulator... Stores the vacuum...

It is suppose to sound like a leak when operating.

Yep... Mine sounded like an air leak ( cause it is an air leak)... I think it is supposed to ' leak' when vacuum is needed ( resupplies vacuum to that black ball looking canister) when there is enough vacuum, the 'air' leak should stop...if you have a vacuum leak, the vacuum generator will his air continuously.. If no vacuum leak, the vacuum generator has gone bad... The part is no longer available... Replace it with an electric vacuum generator... Do a search here for ' vacuum generator'and you will see what others used to fix this 'problem'.. Hope this helps...( there is another vacuum generator in the rear of my breakaway that funishes vacuum to my cruise control...

I just bought the coach, and only have had the diesel running for a few minutes, so does the leak go away in time?

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Since

I have a hard time following this--A vacuum is nothing, so how is nothing stored?? So the little ball has nothing in it, so get rid of it.. English is a funny ie weird way to communicate. No?? Yes??

The device uses the venturi effect to create a vacuum. When the source of compressed air stops, it powers down. It's not a leak, it's a design feature.