This is an interesting article found at http://minniebiz.com/gmcmotorhome/ showing how Armand added inside air recirculation to his 1976, and blocked the outside air to the HVAC in order to improve cooling of the interior of the coach. The mod appears to be implementation of the article "Separating The Hot from Cold" The webpage was printed to a pdf with some of the more relevant photos to preserve the information on this forum.