We have 4 FRF members who own the 290RLT and I haven't read any post where they say the AC isn't adequate.
Louisiana - rippa - Crusader 290RLT
Missouri - Mikecdrd - Crusader 290RLT
New York - 62car9 - Crusader 290RLT
Pennsylvania - kab449 - Crusader 290RLT
Might have the service techs check it again or contact Prime Time and ask them about it. Here's a link; Prime Time Manufacturing, Manufacturers of travel trailers and fifth wheels
Good luck. Hope you find what works for you soon.