Where do I start with A/C restoration?

I think all I need is for the system to be recharged (on an 84 300sd). All of my climate control buttons function and the heater works. Some times ther is a delayed reaction when changing the controls but that's about it. The A/C blows cool but not cold air.

My mechanic told me he can recharge it with R12 and that R12 is pretty expensive. He also informed me that the weak link with MB HVAC systems are leaky AC hoses which are also expensive.

My car sat for almost four years before I began her restoration. Before I pay to recharge my system, is there any sort of shade-tree diagnostic test I can do to check for leaks or other malfunctions?