92 Jetta A/C HELP!

I was wondering if anyone knew how to check the A/C compressor operation on the old 92 jetta diesel. When I slide the control to the "BIG SNOWFLAKE" the rad fan does come on but all I get is warm air. I know it could just need charging but would like to make sur everything else works before wasting the cash. Also I THINK it uses R12 freon which is difficult to get a hold of these days. Does anyone know a cheap alternate? If so what pressure is required? If anyone has any info on how to charge an A/C system I would appreciate that as well.

Thanks for the help!

There is a cheap alternative to R12 that is compatible, They call it Freeze-12 around here. It will, however, give anyone else working on your system with an A/C machine trouble as basically your freon will be "contaminated".