Thanks for all of the replies, gang !!!
I am glad to know the salesman was probably not lying... I think these RV salesmen are worse than politicians... So many of them will say anything to make a sale. I think he said it was working, but most people run the roof units for comfort while on the road. Being new to this type of vehicle, that just did not make sense to me.
It never occurred to me that the coach overall does not have a cooling or heating system robust enough to provide comfort to the whole coach WITHOUT using the RV parts.
I know Prevost is the Gold standard, but who makes the average tour bus/Greyhound? MCI used to have ducts that ran the length of the coach, just below the windows, IIRC... Is an MCI really that much different than a Tiffen or a Newmar? If so, why? You can't tell me that something that costs $300,000 - $500,000 or more brand new is built to be cheaper than a "commercial" grade vehicle. If so, then we all should re-examine this issue, because that means the air bags, brakes, axles, darned near everything are not what I imagine they would or should be.
Please don't take this thread away from coach climate control. BUT, why are the evaporation coils not ducted into the ductwork already in place for the roof units? Is the system used on a tour bus/Greyhound really that different?