I had a similar problem in my Monaco Monarch. I read on this forum that you could take the vent cover off of one of the offending vents, then take the one off next in line to it. Then take a flashlight at one end and a mirror at the other and check for light getting thru. Turned out the duct pipe on mine had gotten crimped and was not letting air pass thru as it should. I used a piece of water hose to work(carefully) into the duct and get it somewhat open. Never got it to work like it should, but it does work.
John- 2011 Fleetwood Southwind 32V