Hi all, I've been having a problem with my heater control that I've seen discussed here before. The diverter control doesn't work, so the air only comes out of the center vents. This will be a problem when I really need the defroster in the winter!

So I took out the HVAC control unit and saw the vacuum line switch. The lever turns the mechanism appropriately, but I have no idea how the thing is supposed to work. I do not hear any hissing when I move the controls around, which makes me think there is a vacuum problem. So then I followed all the lines back and checked the connections, and found they plug into these black pot-like contraptions in back of the glovebox. What are these for? At any rate, there didn't seem to be anything wrong there.

So I followed the pink line up to where it couples to a black line which disappears along with a bunch of wires into the passenger foot well. It comes out, presumably, under the hood at the ECM and terminates behind the engine block. Is there a simple way to determine where the problem is? And if I need to replace a line, what kind of hose do I buy? Thanks much in advance!