Following up on this, with (a.) some additional info my wife provided since
she was the one driving the van when this happened and (b.) some
clarification since I just got back from driving van to church:

1. When it's on the panel setting, cold air is coming out the floor vents.
It's like it's stuck on floor. The air is plenty cold on the floor, BTW, so
I don't think this is an issue with the A/C compressor. And heat is coming
out when I switch it to heat, the air is plenty hot on the floor, so I don't
think it's an actual heating issue. Same with the defrost setting, cold air
and hot air both coming out depending on which I have turned on. We're only
talking the panel setting.

2. This apparently happend spontaneously, the panel vent was working when
she shut the car off when she got to one place she was going. When she got
back into the van headed home and turned the a/c on, the panel vent was no
longer working. I asked my wife if she'd hit any bumps, done anything with
the buttons, heard anything unusual, she said no.

3. When it's on "hi/lo" setting, no air is coming out the panel vents, just
the floor.

4. As I said, there are two little vents on opposite ends of the dash where
air comes out, those are working. However, on this particular van there are
two other little vents right underneath the steering wheel that blow on the
driver. They are not working.

Does this narrow things down any more or are we still looking at both
possibilities? I posted thinking there might be something I could do to this
today, looks like I"m going to be at my mechanic's in the a.m., though.

Thanks!