fact AC genius help needed

[Blazer Steve]

OK guys need some help

Have great working factory ac with exception of high speed. I know the relay is normally the culprit, but it looks new and have tested and it seems to work. I haven't swap it out, was wondering if someone had any other ideas

Also, was there a factory heater core shut off that was controlled by the ac controls? my ac guy says he believes these trucks had one, and I have holes where one would be mounted on the rt inner fender in line with the heater hoses
Thoughts?