He's got a 78 SC, likely with a York compressor. Enough said. Ditch it and call Charlie Griffiths (Mr. Kuehl above) and get a Nippondenso or Sanden. That would be a good place to start. If you're going to get serious about your a/c, you should also replace your hoses with barrier hoses. From there it becomes a very slippery slope.
Have fun!