R12 is dichlorodifluoromethane. Used in AC until the early 90s and as "canned air duster" and those little pocket airhorns until the late 80s or early 90s.
R134a is 1,1,1,2-tetrafluoroethane. Used as AC until the present day and as "canned air duster" and those little pocket airhorns until the mid 00s, iirc.
R152a is 1,1-difluoroethane. Used as an R12 substitute (with the proper lubrication oil) by nerds like me, and currently used as "canned air duster" and those little pocket airhorns. (seeing a pattern yet? :roll
If you go to your local chinesium dealership (Harbor Freight) and find the Ultra Duster cans on the shelf - they are R152a with bitterant added. Currently priced at $4.99 for a 10oz can. My wife's Roadmaster AC system actually has 3 cans of that in it... I didn't feel like finding a vendor for "R152a" as a refrigerant. Been working great for a year or two now.
The best part? It works just as well as R12 (R134a requires larger condenser and evaporator coils to provide the same cooling) and has a much lower GWP and ODP than most other currently available refrigerants. AND it's cheaper.