Chevrolet Repair: 1979 Camaro A/C, 79 camaro, pipe thread

Question
I have a 79 Camaro with a 350. I bought the car from the son of the original owner. Good condition. The air conditioning was probably the best I've ever seen in a car. Then it stopped working. Every time I turned it on it would make a horribly loud noise. It wouldn't blow cold air so I finally unplugged it. I don't know alot about under the hood but I knew it was A/C so I unplugged it. What's making the noise and how do I fix it?

Answer
If you unplug the compressor and the noise goes away completely you have probably already diagnosed the problem.  Has the system been changed to a HFC (hydrofloralcarbon)(R134a,Redtech, Blend)? or is it still an CFC (chlorofluorocarbons)(R12, R22) or a Hydrocarbon?
  This can make a difference on the type of repair I would suggest.  Look at the fill ports and see if they are threaded 1/4" pipe thread on the low side or a funny looking fat quick connect.

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