Thanks for the ideas. I had previously checked the roof and as much of the duct I could see behind the endc ap (had fears a bird find its way in there and was building a nest with the duct!) but all looked good.
I ignored the A/C drain because it had been steadily dripping water. I checked it at your recommendation, and sure enough, water came rushing out after giving it a little squeeze.
Again, thanks for the help!
Originally Posted by KIX
We have the same A/C system as you. Cool air flows from the basement A/C inside the rear cap to the ceiling distribution registers. The duct is simply a hollowed out track in the styrofoam ceiling insulation. IMHO you have three possible sources.
1. Condensation. But for that to be happening you would have to have a source of humid air inside coach. LIke leaving doors/windows open while running A/.C.
2. Roof leak near rear cap to roof joint allowing water to penetrate into duct.
3. A/C pan drain stopped up. Under A/C unit is a rubber duck bill valve that allows condensate water to drain from A/C pan. Is this drain allowing water to drain?
I hope this helps you find and fix your problem.