Bendix Brakes won't air up

[Al]

We just had the brakes serviced by McDonald Coachworks and everything
seemed ok. Now are are in our 2nd week of vacation and we shut down
like normal and jacked the bird up. Been here for 3 days and now we
are ready to head to Charlotte, NC and the brakes will not air up. I
hear a hissing sound at the Bendix valve. Looking thru my manual now
as to what to do to get the valve to close so we can air up our brake
system. I have searched the site and dont see anything that would
lead me as to what to do next. I have tried turning off the engine
and letting sit and restart with no result so far.

Thanks for anyone that responds.
Al, Kathy Alfred, Daniel Johnson
Bear Den Campground Spruce Pine, NC
'96 BMC