328 Airconditioning

My airconditioner has recently ceased making cold air. It ran fine last week on about a 30 mile trip and then never came on for the return that afternoon. The fan still comes on and blows fine. I then checked under the hood and the compressor clutch is not engaging. I unplugged the wire to the clutch and it registered only .71 volts. I assume that it should have 12 volts at the clutch. Does anyone have an idea? I do not have a wiring diagram for the car and if anyone knows a source for the wiring diagram, I would be most appreciative. My assumption, right now, is that it is an electrical problem but to test that theory I did run twelve volts directly to the compressor clutch, started the engine, and still got no cold air. It may turn out that the freon left and the clutch is not engaging because of the low pressure switch cutout. Anyway, any suggestions would be appreciated. I figured, at least, I should go through the electrical side first since I will have to pull the wheel, the wheel well and the air cleaner housing to check the freon.