A/C Issues. Vacuum problem?

OK, so at first when I bought my '87, I though the A/C motor was shot. After some investigating, turns out it's not, but my controls are. The only air I can feel comes out of the vents up on the dash (the defrost vents by the windshield) and I can feel the temp change when I use that control. I can also change it from low power to high power. What I can't change is where the air is directed. I will move the switch, and I can hear it clunking inside, but nothing changes. A friend of mine said it was probably a vacuum problem, but he didn't elaborate on that.

A vacuum line runs from the engine to a "t", located on the passenger side, in the engine compartment. From the "t", the line runs to the little plastic bottle under the grill, and through the firewall, to controls under the dash.
The vacuum is used to open and close "flapper" doors to direct heat/cold to the appropriate places, depending on what you select.
These doors have "fail safe" positions, that, in the absence of vacuum, they will assume a "relaxed" position.
You control the vacuum via the selector switch on the dash.
A failure with the selector switch, or a leaking/broken vacuum line, or vacuum motor can cause your problem.
Bad vacuum lines are common on the older XJ's.
If I were you, As a beginning, Id start at the vacuum reservoir bottle, and replace all hoses . If your '87 has original hoses, they are probably in need of replacement now, or in the near future, due to age. So change them now, and save future head aches.