Meineke broke my air vent damper

I've run into a problem with my air vents not blowing any air, except from the floor, and I think the defrost, if I tell it to. What happened was, I took my 1990 to Meineke to get a non-start issue resolved, where they didn't find a problem per-se, but did tell me that my intake manifold was gross. So I got them to clean it and do a fuel system treatment. I got the car back (this was last fall) and it worked fine, but I didn't notice the damper problem until I was on the road to school, and I couldn't turn around to make them fix it. Now, I want to fix it myself as summer is here and I want air on my FACE. I do know that it was something they did, as nothing was wrong before I took it in, and it never worked after I got it back.

I don't know how much cleaning the manifold and all would affect the air, but I did notice a broken tube at the firewall connected to a brick-sized black plastic box, near the top of the firewall. The tube is broken at the box and had a screw in the end of it (!). I removed the mysterious box and found that it was hollow. I bolted it back in and started my car while holding the tube to the broken opening, but the air damper still would not move the air to the vents. What could this be? I don't have a service manual yet (been searching ebay for months) so I can't troubleshoot this as the Haines has nothing. Anyone know what I can check?

The square box is your vaccum tank, without vaccum the actuators cannot work. Repair or replace the tank and your vents should work properly.

thanks Flatrater. I didn't know for sure if it was that or not. I'll try and post my findings.