The difference is the gas type. What I know , R12 gas have CFC, not good for ur ozone , last time to refill gas for proton 5 year ago around rm10-13, but now my mech said rm20-30 market price. That is because our goverment dont want we used this type of gas so now the gas price was increase. 1 tong around 300++. R134 last time to refill for wira its take cost around rm60-80. but now rm 40 - 50. because now many car used that type of gas so the price drop la..
Difference R12 with R134 compressor, R12 running rotary style but R134 used piston. so it more silent. So if ur compressor big + more piston , ur a/c more efficien and more cool. R12 compressor if the condition not so good like sound more noise ur a/c not so cool when ur running idle, exspecially in the hot day...
that what I know.. correct me if im wrong. cheers...