One of the FT's were traveling with (2001 36'U320) has no air to blow the Hadleys after sitting overnight. Where's the likely leak?
You need to look at the air system diagram for that coach and see where the air horns get their air supply.
On our '93 U280, for instance, the air horn supply solenoid is T'ed off one of the air lines that feeds the dash air pressure gauge. That air line comes directly off the front brake tank (bypassing the protection valve). So, on our coach, any leak that depletes the pressure in the front brake tank will affect horn operation.
Your travel companion's coach may be plumbed in a similar manner, but the only way to know for sure is to consult the appropriate air system diagram.
Ours stopped once but our air horn solenoid is under the dash top close to the ignition solenoid. The wire had pulled off and just needed to be plugged back in. Easy to find.
Pierce
From Hadley Horn Company.
It's probably what Pierce said.
I had the same problem and it was a small air line connected to the solenoid under the dash. I pulled the top cover off the dash and removed the line, shortened it, and reconnected it in less than fifteen minutes.
Dave & Kathy Bennett
2004 U270
Must not have been a big problem since we never heard back from the OP.