88 420SEL A/C Repair Possible?

I have a 1988 420SEL with 115k miles. The A/C does not work properly -- the discharge air does not stay cool when the car is idling in traffic, but it does get cool when driving at freeway speeds. It acts like other cars I've had that needed a can or two of Freon, back in the old daze.

I am completely ignorant of the new regulations for A/C repair -- is it possible for me to get this air conditioning repaired as a Freon system, or do I have to convert to R134a? I've heard all kinds of stories from different shops in the Los Angeles area, and I could use your expert advice, please!

Thanks in advance... -- Jasper.