Medico

Here is a thread on how we did just this.

You are most likely correct. We do have an evaporator unit under our bed that supplies the rear AC when under way. Like I said, I was just guessing what might be wrong. Since there haven't been too many responses, guesses may be all that is available at this time.

I wonder if part of the problem is that the engine is in the rear. I know on my coach when I turn the AC on in the bedroom (AC from engine, not heat pumps) it cuts down the amount of AC coming from the dash. I believe the dash AC is similar to an automobile in that a compressor on the engine supplies the cooling. It's a long run from the engine to the dash AC. I wonder if you could find the air runs and insulate them some??? Just a "wag" here. Have you actually taken it to a coach service center rather than just an AC shop? Sorry I have no real ideas for you.