MiracleJ,
I agree, it would almost have to be a stopped up drain line. If your coach has an air hose connection in the engine compartment you can just blow out the drain line using it. Most Newells have an air chuck in the engine compartment where you can plug in an air hose - comes in handy for airing up your tires too.
If you don't have an air hose/connection maybe a water hose would work. It's been a while since I have fooled with roof ACs. My last 2 coaches had basement ACs.
I'm sure it will be a simple fix.
