About the A/C Units
I believe you may be looking at the A/C outlets in the ceiling, which are circular, with vanes that can be directed. You can increase the flow to these by closing the louvers on the bottom of the A/C unit itself, on the ceiling. The inlet for the A/C unit (like residential window units) is on the outside of the A/C, up on the roof. When the slides are in, the cooled air finds its way around the closed slide, and into the bus. You could open the louvers on the bottom (outlet) of the A/C unit to have the A/C cool air come unrestricted into the bus with the slides closed. Only down south in the summer do I operate the generator to power the front A/C while driving (slides closed), as the automotive A/C isn't quite enough.
When the front A/C unit is operating in heat pump mode (only is effective when outside air temp is above 40 - 45 deg F), heat comes out of the circular A/C outlets.
A Little About the Furnaces
The heater outlets from the rear furnace (in my 2013 390RB-40L) are registers in the floor of the bedroom, and circular, brown plastic vents with louvers in the bathroom and front half-bath, on the wall near the floor. The front furnace outlet comes out under the couch in the front, on the right, opposite the table, through a plenum system built out of "construction wood", as FR calls it. Open up the couch into a bed, and remove the thin, fiberboard or plywood cover to view it (again, design may vary with model - I have the Rear Bath Model).