I have a 1989 Chevy S-10 Blazer, I bought it in 2003.  The air
conditioner has never worked since my purchase, and I don't know why,
and with summer approaching again, I'd like to try and get it fixed
this year.  Here is my problem(s):  when I put the selector switch on
A/C or on Defrost, the fuse blows, either immediately or very soon
thereafter.  So, I have to keep it on either Vent or Heater.  However,
when it is on Vent, I get some air blowing out of the vents, and some
blowing out on the floor.  When I put the selector on Heater, I get
some air coming out of the front window defroster and some blowing out
on the floor.   The blower works fine on all 4 speeds.

Any help would be really appreciated.  I don't know much at all about
auto a/c systems.