got a quick question for ya'll

[southernmutt33]

ok i got a 84 3/4 gmc with a 454, granny 4 spd....ok i just got the truck about 6 months ago...i noticed that the a/c was unplugged under the hood....the other day i figured i would plug it in to see if it worked....ok it works, but the a/c compressor ,akes the gawd afulest screaching noise you have ever heard. ok i dont know anything about a/c other than they work or dont work....so bear with me if i dont know all the correct part names.....ok can you just replace the pully assembly or does it have a clutch like a fan..or do you have to replace the whole thing....is there a way to oil it or add a lubricant to it....once you start driving it it does quite down an somtimes doesnt do it at all.....but it always comes back...so i dont know if it is doing it just because it hasnt been used in a long time or what.....it does blow cold air, not as cold as my 98 taurus, but is quite cool...may need to be recharged....