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.
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.
r 134
First of all, you don't use R12. Rather, R134 which has the oil included.
R12 unless it has been converted. I would convert it over to R134 due to the price of R12.
A 1999 Ford Mustang has r134a in the air conditioning system
It came from the factory with R12. Unless it has already been converted which you will know by a sticker placed somewhere on the system, I would most definitely have it repaired and then converter over to R134. R12 is just too expensive to consider using.
R134a.
It takes R134. R12 is no longer used in vehicles produced around 1990 and newer. Every vechicle from 95 and on uses R134A. Some cars may have even started converting over to r134 as early as 93 but officially EVERY VEHICLE from 95 and on has r134
Should be R134
To convert an R12 system to R134 all of the R12 will have to be removed. The system will have to be completely flushed out then special additives installed. This is done due to the way the different Freon's react to the systems gaskets. After this is done then the system is ready to be set up with new Freon.
Don't. R12 is so very expensive that you should have your vehicle converted over to use R134. You have a leak or you would be needing to add refrigerant. Have the leak repaired by a professional and have the system converted over to R134. The will remove all R12 & the oil from the system and replace it with R134 & the correct oil. They should pay you for the R12 due to how valuable it is. You may end up spending very little on this repair.
Your 92' Geo probably uses R12 freon, but since they don't sell that to just anybody in stores they will probably want to sell you R134 freon. I recommend that you just take it to somebody who has an air conditioning license that way he can get you the R12 that it needs. I wouldn't put R134 in your air conditioning system because it might harm it. Plus R12 is very expensive now a days since they don't make R12 systems for cars anymore cause it pollutes the atmosphere, but to tell you the truth it cools alot better than R134. R134 is sort of like the replacement of R12. A can of R12 can cost up to $30, and most cars need around 2 or 2 1/2 cans.