Vent Help Please, no longer supplied with vacuum?

[C10CONFUSED82]

Forum members a I am having a issue with the vents on my 82 C10. The truck has a 5.3 swap. The issue that I am having is that the vents that are in the truck do not work. Like when I switch my HVAC control setting to vent the vents do not open. Seems to me like there are vacuum lines connected to them. I am thinking that the lines are no longer getting supplied with vacuum since the 5.3 swap. Is their anyway to supply vacuum again to the vents? Is the problem a vacuum issue? What do you all think? Really would appreciate help since my truck gets really foggy in the cab when it rains. Pictures or diagrams really would be great also, would make it easer to follow instructions.