Sorry for the late response. I did not fix the hissing sound yet. Theres a rubber block on the back of the vent control ****. I recently got a parts truck so that's one of the pieces I plan on swapping when I get some time.

 

There is also a 'block' under the dash. Pull the carpet back at the top of the hump and its right there. Maybe one of the vac lines came off. White, red, blue and from there I don't remember.

 

Thanks, Glenn. I'll see if I can find it this weekend, if it isn't raining again.

I could feel the back of the control know and found a "vent" hose? It felt very short, but I could definitely feel the end of it was open.