My interior AC/Heat/Defrost/Vent fan doesn't work, except in the HIGH position. So, it's all or nothing, if you know what I mean. also, my cig lighter haws been out for a long time.

Yikes!

check fuses

fuse for fan is OK. I replaced the interior air filter, thinking the air intake may be clogged. the high worked better, but still no low fans. are they two different motors / circuits?

cig lighter seems to have a short. when I replace the fuse, it blows right away.

check ALL fuses. did you check the HVAC fuse?

have anything plugged into the lighter? commonly the short is right at the lighter, not the wiring. did somebody shove a penny in there?

Sounds like the resistor board assembly is bad. This is a common problem on other GM vehicles. Here is a repair procedure for Pontiac Montana, should be similiar on the buick though:

"blower motor resistor. Easy to replace the ceramic card containing resistor and relay. Take off passenger side panel under dashboard. Stand on your head and disconnect wires to blower motor and wires to left of blower (which connect to resistor board). On the resistor board (which has the wires to the blower now dangling), just loosen the two screws closest to the firewall (don't remove them because they're hard to get back into place -- take my word for it). Then remove the center screw that's easy to get to. The resistor card can be removed by sliding back (it fits in a slot like a drawer). Reverse this procedure to put it back after you've purchased the replacement card from your dealer. Don't force anything or you'll break the new card -- it'll slide into the slot fairly easily when it's properly aligned."