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.
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.
R134a.
The 1996 Suburban uses r134 Freon. The fittings to add Freon are different sizes on r12 and r134, making it impossible to add the wrong type to your vehicle.
Should be R134
Check the ports to add freon--the low side is a large hose --the high pressure is the small line--on the large line if the valve is the large style----the freon is R134--if the valve is the small style it is R12--no longer used --retro valves are available to convert R12 systems to R134 R12 fittings can't be connected to R134 gauges, and vice versa. If it's R12 you won't be able to connect the hose from the supply can to fill it, or do anything else with R134 equipment.
You do not want to buy Freon as it is very, very, expensive. Have the leak repaired, the system purged of all Freon R12 and the oil. Have it converted over to R134 refrigerant. You cannot just add R134 as the oil used in R12 is not compatible with R134. You will be money ahead by converting it.
R12 134A pre 1996 is r12, after is r134
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.
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.