134 can work fairly well with a good compressor, a clean condenser, a fully flushed set of coils, a new expansion valve, a new reciever/dryer, and an EXACT amount of oil in the system.
fairly well means up to about 90F outside and driving in a lot of shade, on the highway, you will get decent cooling from the vents. it'll take a LONG time to cool a car in hot sun, with no tint on the windows, at idle. If your area sees 90+F high humidity days regularly, you should strongly consider using R12.
you still need to flush the coils, and clean the condenser and straighten all the fins, and change the reciever/dryer and the expansion valve, and add the exact amount of oil, but the efficiency of the refrigerant will net you 40F temps at the vents on HIGH in 95degree days in high humidity, and cooling will be far superior.
it'll still be hot on super hot days, the 123 a/c is poorly designed, get used to it if you live in the ultra hot areas. and tint the windows. it'll help!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!