[ddsmith]

You got to love when a pop-up takes out some stuff you already typed. Very strange. Anyway I wrote that I believe both systems are design to be 100% recirc air. I know that the Old Air is that way. I don't believe that not having fresh air position causes the fogging of the glass. I think it is caused by defroster damper leakby. The damper is cable operated and can be fiddled with until you get the adjustment you like. Just as a tidbit of information gained from the Old Air unit install. If you must have some outside air drawn into the cab and you are using a factory A/C control panel you can leave the vacuum hoses and can attached to the truck. One of the ports on the control panel vacuum valve provides vacuum to the kick panel vent and opens it. This is provided it was an A/C factory cab. If it is not then you would need an A/C control panel and the damper actuation diaphragm. The top lever of the controller is what makes this work and on my install the top lever does nothing now. Bringing in fresh air will raise vent temperatures and raise in vent temps which will in turn reduce windshield fogging if the defroster ducts are leaking by. An added benefit is the unit draws air from the passenger foot well area which is were the kick panel vent provides air. Hope this information will help.