I'm in a process of rebuilding the entire a/c system in my 90 k5, 5.7L.
I've noticed that the flap, that supposed to provide the ability to circulate cold air from the car, isn't sealing the fender at all - which, by my logic, means that the blower is also sucking warm air from outside, and by this - dropping significantly the "final temperature" of the air that comes of of the louvers.
I'm assuming for a second that I'm right - is there a chance that the inside of my fender is missing a piece?
any info will be useful because I've already replaced almost the entire system and it preform poorly. (compressor was not replaced... yet )

 

When "max ac" is selected, the flap should seal the outside air from coming in.

 

that's exactly what's I'm saying. and because the blower, the evaporator and cover were removed from the truck during the rebuild, i saw the inside of the fender and discovered that there's no way that little flap can seal that entire space.