Heater Box

[oltronj]

I have a 1990 GMC suburban with a/c that the heater is giving me problems. It always is blowing out of the vents, I have vacuum to everything that I can find to test. Is there a way to get to the vacuum actuator that is on the back of the box by the firewall? Or at least a way to look inside there and see if it is even trying to move? The other question is does anyone have some advice on pulling the whole box out, I have used the search tool here and have found all kinds of pictures of ones that are already out but not much for advice on actually pulling it out.