Mazda Repair: AC problems, fan blows air, expansion valve

Question
I just purchased a 1990 Miata.  I knew the AC does not work.  It blows air but not cool.  My friend's 1993 Miata has the same problem.  She had freeon put in, and it still does not cool.  The compressor in both work fine, as the fan blows air as well.  Is this a common problem with Miata's.  Do you have any suggestions or have  knowledge of know of this problem.

Thanks

Answer
Been out of town.  Sorry.  If you charged the system and you visually see the compressor hub engaged and spinning but have no cold air and no circulation then:

a. the compressor has internal reed failure and cannot compress
b. the hub itself is slipping and it is not getting engagement (look at it all very closely) a slipped hub can appear to work properly.  (look where the rubber meets the metal ring of the clutch face)
c. you have a line blockage most likely the expansion valve inside the evaporator assembly under the dash.  The receiver/drier will need to be replaced also as it is a filter for the system.