According to the printout I have in my binder, the vacuum outlets correspond as follows:

y1 - fresh/recirc (small lift)
y2 - fresh/recirc (large lift)
y3 - footwell
y4 - center nozzle
y5 - defroster (large lift)
y6 - diverter
y7 - defroster (small lift)

According to the page, it is for vehicles after 09/86, but I didn't print out the other pages of the manual entry, and don't know if they are different for later vehicles.

Only two of the vacuum pods are easily accessible, I think. If you're going to R&R the dash to get at the other ones, you should probably do them all at once.

-anthony