[drone]

A year ago I switched two older cars from R-12 to R-134a, they both are doing well today. What you need to do is first determine if your system has leakage and fix it. As R-134a is a smaller molecule it will escape much quicker than R-12. Switching over may be more complicated than the average individual cares to take on. You'll need a couple of pieces of equipment to do the job, a good vacuum pump and a refrigerant manifold valve with appropriate hoses and 6 oz of POE oil, (polyolester, from Autozone, ect)and a suitable reference chart from the library or autoparts store. You'll need to drain out any remaining R-12 from the system. The POE oil is compatable with the R-134a coolant. Chances are that all the old mineral oil from the R-12 charge has long ago leaked out so don't worry about mixing the two, I didn't and I haven't had a problem. After bleeding out any remaining R-12 you need to add the 6 oz of POE oil to the system. Find the best way to do this, you may need to remove one of the lines at the compressor. If you remove any lines you must replace the gasket with a compatable one. Once the oil is in you need to draw down the system with the vacuum pump. Hook up the manifold per instructions with the gage set and suck it down for over an hour at 29" or so. Test to make sure the system holds vacuum. If it doesn't, you have a leak, stop and fix it. If the system holds vacuum start hooking up the 134a hoses to the manifold and begin filling. Stop the vacuum pump. Start filling with the engine off then proceed with the engine running. You will need around 3 pounds to fill the system so make sure you know how many cans or use a scale if filling with a 30 lb. tank. Make sure the can is upright to dispense gas, upside down will dispense liquid. The compressor will cycle on and off with a corresponding pressure reading. Check the recommended pressures in the book or just stick with the 3 lb deal. Once you have the required amount of R-134a into the system, shut off the engine and remove the hoses. Check out the internet, there are many articles describing this proceedure.

[oldcomputerguy]

Telling someone to add 3 pounds of r-134a to a car for which you have no idea of the make/model is irresponsible. The system is either charged to exact weight which is posted on the car or slightly less if converting. In the conversion process the system is often charged by pressure at 2x ambient temperature plus 40 psi for r-12 or plus 60 pounds for r-134a. 48 oz of r-134a would probably blow the safety plug on the compressor assuming it had one.....or it would blow the compressor.