I need to get new A/C for my '92, which I think has the old R-4 refrigerant. I've hearad there are several options. All I care about is which option is the coldest for living in the South.

 

You probably hace R-12 in there unless it was updated before. In the mid 90's there was a whole bunch of different refrigerents available, and none of them were compatible with each other. The only option available today is r134a. The conversion kit is like $30 and most shops charge 1-2 hours labor to do it.

-Jon