M.B Doc, Maybe you know what I am talking about
I have my blower housing unit exposed right now. The dash was removed. I removed the top cover of the center housing for the heat exchanger or heater. with a mirror I can see that there is no flap or door to close the air delivery from the evaporator to the top cover. That means that the center outlet is always delivering air as long as the blower is on. The only way to close it is manually at the adjusment in the dash itself. I remember that before the air delivery was controlled automatically and that sometimes there was no air delivery through the center outlet. I noticed this after sending the car to an A/C shop for repair. They replace the evaporator, but I am not sure if they modified the housing. At this point there is a perpetual air delivery through the center outlet unless you close it manually. There is no flapper controlled by the vaccum elements that can close this area between the heat exchanger and the evaporator. There is one flapper with a vaccum element that controlled the air delivery after going through the heater then through the center outlet though. But closing it does not stop the air flow through the center outlet. Please reply if you can understand what I'm talking about.