One solution is to commit to a total replacement with the upfront costs often offset over a fairly short period of time by the higher efficiencies of the latest models.
Still, if an older unit can be retrofitted with some non-CFC refrigerant, that might be the way to go. And it was the route the NutraSweet® Company went when it came to its manufacturing plant in Augusta, Ga. That facility had a 30-year-old, 1,100-ton R-12 chiller.