How To Troubleshoot 83 Mercedes 300SD A/C?

There is not too much to this AC system. The first thing to do is to make sure that there is enough refrigerant in the system. Unfortunately this was the old R12 stuff, really should change to the new r134a stuff. This is not all that hard, change a few o-rings and the valve behind the glove compartment.

Next is the temperature control thing in the dashboard. These often have bad solder joints. After the system is recharged see if it all works. If there is a problem with temperature adjustment then this control thing must be replaced. I think I have an old one around you could have.