Bill,
I'd start by removing the load wires and seeing if it will stay closed. If not, bad breaker. If it does stay closed, check for chafing where the wires enter the AC unit and where they exit the breaker box. Can't help as to junction box but not sure why one would be employed if that AC is only load on the breaker. Diagrams of 03 Pats show dedicated breakers with direct line from breaker to AC.
Steve