Brother of The Benz
Alex, as mentiond if you have a leak in your A/C it must be repaired.
In finding the leak it is cheaper to pressurize the system using $5.95 per can of R134A than $40.00 per can R12.
You will recieve a ton of how to do it from the replacing of major components and "O" ring seals to the Gas Tank Cap.
I have a 1987 W124030 that is running R134A and I am very pleased with the performance of the Refrigirant.
Changing to the new gas is simple.
You will need a Kit that can be purchased at all auto parts houses as well as K-Mart, that's where I get my supplies. In addition a manifold gauge set and hoses.
You purge your system of R12 using a recovery system provided by your friendly A/C service center. I don't know what they charge where you are for this service. I know of others who just vent the gas to the atmosphere but you do what you think is right.
After repairing the leak, evacuate the system using a vacuum pump. There has been different opinions as to how long and to what pressure to pump down to. I will say that pump to the blank off of the pump and a little time more.
The conversion kit comes complete with compatable oil charge, 3 12oz. cans of R134a, a can tapper, new service valve fittings, and a service hose.
With the system at minus pressure you add the oil charge first, then the R134A gas.
You reduce the quanity to 75-80% of the R12 capacity. If your system used 3.5lbs. of R12 you would charge using 2.625-2.8lbs. of R134A. The capacity of the R134A can is 12oz. For 2.625lbs(42oz) would require 3.5 cans.
That's all there is to it.
You probably won't be able to tell the difference in the cooling between to 2 gases, I haven't.
Place the labels noting the system is R134A and you just made a conversion.
Listen to all of the different ways you will be told of and then make your choice about this very simple and inexpensive job.
Happy Trails Beep Beep from The Spiderman in Houston!!!