1992 S-10 Blazer Air Conditioning Problem

Can anyone help me, I have a 1992 Chevy S-10 Blazer that I cannot get the compressor clutch to kick in. Should you be able to apply voltage to the compressor connector and the clutch engage or is it just a switch? Anyway, not sure where else to go, I am a student and don't have alot of money to get it fixed. Guy I bought it from said it had been working great, system is charged but I did not think that would make a differece whether clutch would engage or not. Any help would be appreciated.