Air Cond. Troubleshooting

First, thanks very much for taking the time to render any assistance. I have an '80 300td non-turbo. Air doesn't work = big problem in S. Fla...any suggestions on troubleshooting? I understand that there are two climate control units, one under the hood, and one behind the dash unit. By the way, a tech told me that a/c lub. oil was leaking (at the hose assembly at/from the compressor). Help! no one will ride with me!...on the other hand....
thanks a lot