I don't know how much you've run this A/C or where (dust, etc.) but here is
Chris Bryant's How To for cleaning a rooftop A/C. We had a 20+ year-old Coleman Mach that I thought we'd have to replace. Cleaned it Chris' way and it went back to cooling very well.
The Mach on our current coach isn't as old, but it was used a lot and was a real mess. Cleaned it and it cools like crazy now. On this one, I pulled the blower motor and cleaned the indoor squirrel cage. Its fins were all fouled with greasy dirt.
I rinse the evaporator (indoor) coil differently than Chris shows. I use a metal deflector (expired license plate) to keep water away from the passage to the coach interior. Then I flush the coil with a spray nozzle on a garden hose. A pressure sprayer for insecticide works well without quite the risk of spraying water inside.
Both of our Mach units were Ductless. I imagine Ducted would not provide as many degrees of "split" (difference between inlet and discharge air temps) as Ductless does.
If yours is Ducted, try to check to see how well the Ducting is connected to the machine's Discharge.
