All 1998-2000 Tradewinds are built on Freightliner chassis.
I'd suggest checking to see if the air flow diverters are operating. Open the access to the generator and look at the plentum above it. There should be two openings, and those openings should close when the A/C is on, at least I think they should close. I'm sure they'd be closed if you had the A/C on 'recirculate'.
If the doors inside these openings don't close, maybe all your heated or cooled air is going outside.
2012 Allegro Bus 36qsp