duster is 152a difluoroethane..... 134a is tetrafluoroethane. so they want the same type of oil. pag or ester. ester is compatible with mineral oil that R12 used so its a better choice for those vehicles.
im going to get my AC back in my reliant soon. i have a hose crimper so i can make some custom lines to put a parallel flow condenser in the front of the car without much hassle.
other tips.... just find and fix leaks. you can put UV dye in the system and find leaks with a UV flashlight. heck you can usually see leaks at fittings or if a rock/corrosion put a hole in the condenser.
dont overfill. if the car called for X amount of R12, it will take less 134a to be fully charged and even less 152a duster.
i will put close to what its supposed to have in the system and then use a thermocouple meter (cheap harbor freight multimeter that came with an exposed junction k thermocouple) stuffed in the largest vent to watch the temp as it cycles on and off. itll fluctuate up and down pretty repeatably. i keep adding as long as its falling and the pressures on the gauges are within spec. (find the factory temp/pressure charts) as soon as it jumps up one degree, i stop.
hasnt failed me yet. my neon had ice cold ac. in the 30's (F) when it was in the high 80's with the car sitting stationary in the sun.
my 07 town and country has the rear ac blocked off (leaks back there... put blockoff plugs in) and filled with duster. it freezes us out in the summer no problem even with only one evaporator.
subaru has some corroded aluminum where an oring is supposed to seal so it leaks down slowly.... needs a recharge every spring.... with duster lol. its compressor has 300k miles on it and is kinda worn out so it doesnt cool quite as good as my van but it gets the job done.
i just bought a 02 Honda CR-V (new turbo project
5-speed and AWD) and at some point it will probably get duster lol. the previous owner had an issue with the AC and had EVERYTHING replaced. yippie for me.
Brian