Help with heater valve
 

Few years back I changed out my heater core on my 1993. Got everything back together and working. Only one thing that bothered me was that the slider that controls the hot/cold seems to jam before reaching the end of the slide. And, im pretty sure it is not fully closing when i push it all the way over to the cold side. I can't remember how to adjust this thing. Anyone have any idea on the procedure for this? Thanks