Restarting A/C on an 85 W123

[rmmagow]

I do not know when the A/C last worked on the car. There is a retrofit R134A connector screwed onto the low pressure side. As far as I can tell, no refrigerant in the system or super low.
Let me know if this is a reasonable approach to trying to evaluate the system's state of being.
Electrical things all seem to be in place, it think there's even a high pressure cut-out switch that is supposed to be used when going to R134A.
I am going to get a vacuum pump and do a long running vacuum pull and see if the system can hold vacuum at least for a couple of hours. If it can I will then attempt to put in some R134A through the low side, engine off. Once there's a can or so in there, I'll crank it up and see what if anything happens.
Longer term, I am thinking to disassemble and flush the system and replace as many o-rings as I can find. I want to convert back to R12 as I have a lot of it and I suspect it'll work better.
Does my evaluation approach seem reasonable?