OK, I keep seeing so many of us having troubles with it being too dad-gum hot in the summer, and too friggin' cold in the winter, so I thought I would give some info I've found to be right on the money.
There is a book available, written by an ASE Certified Tech., and he's one of us! He owns (or did) a '69 coupe!
The book is..."Air Conditioning Stategies for the 63-82 Corvette", written by Michael J. Davis. I have seen it advertised in several of the 'mail-order' vendor's catalogs, but you might have to look for it. (I bought mine several years ago at a car show.)
The book covers the basic theories of the A/C systems; why they work, why they don't, and how to FIX them. It gives temp. measurements before and after different ideas he tried, and gives valuable tips on where to look for leaks (air) in the ductwork, etc., and how to fix them, and insulation tips.
My '74 is an A/C car, but it also has a black, leather interior, and I live in Texas, so you can imagine how hot it can get if the A/C ain't-a-workin'! I can now cruize comfortably in the heat of summer, and the info in this book was an unbelievable help!