HVAC vacuum leak, only defrost & floor work, no vent! on my 1st Gen S10 Blazer - Part 28

I troubleshoot why the HVAC only blows on the floor or defrost, it will not blow through the vents. Using my trusty Mighty-vac I find the problem and use a work-around to get it blowing through the vents again!
I picked up this 1st Gen '94 S-10 Blazer as a project to stuff a motor and transmission in that I had recently removed from a later model pickup. I will go through real-life experiences with Ya'll straight from my garage, just like most of you have to do. I have been working on cars most of my life and sometimes I enjoy the work while other times I do not. I am sure we will go though both of those times while working on this project.