No, if you mix them they will gel and ruin the compressor and other components. Also, the oil that is used in the r12 system is not compatible with r134a and will not flow thru the system properly causing the clutch on compressor to not disengage. If you decide to retro fit your vehicle your need to replace compressor, orfice, condensor, the fittings and evaporator, so pretty much all the components and the system need to be evacuated and vacuumed so there willnot be any moisture or air in the system. And keep in mind r134a does not get as cold as r12
If you mix r12 with r134 air conditioning system, it will cause a high pressure in your airconditioning system and eventually damage the compressor and the evaporator. R12 is only for r12 aircon and something with r134, it can't be mix.
They should never be mixed.
Only if you're trying to destroy your AC system. Never mix refrigerants.
Why would you want to even consider doing this? R12 is no longer in production and as such it cost almost 4 times as much as R134. But to answer your question, use R12 in a R134 system and you will destroy the compressor as the oil is not compatible with R134 oil.
R134a.
Should be R134
R12 134A pre 1996 is r12, after is r134
Unless It Has Been Refitted For R134 It Will Use R12. Best Way To Work This: Have A Good A/C Tech Update To R134 And Test Your System. You Will No Longer Be Able To Get R12 Well Some People Have Some Stashed About ( Cost Is High ) There Is Supposed To Be A Freon That Will Mix With R12 But I Have Heard That It Will Not Cool As Well. Good Luck
R134a
r 134
If if it a 1995 or older then it came with R12 installed. 1996 can be R12 or R134. 1997 up, it has R134/R134a. If you suspect it had R12 look for a label somewhere on the A/C unit signifying it has been converted. If you find it has R12 and is leaking and needs repairing, after the leak is repaired, convert it to R134a. R12 is far too expensive to use.
First of all, you don't use R12. Rather, R134 which has the oil included.