My 1996 850 has developed the dread R134a leak that requires you to take the dash apart to replace the unit. Its a slow leak and I've been able to recharge the system to keep it working. The question is I assume I'm also losing compressor oil and probably put some more in. This is the original equipment on the car. Which oil should I use. Esther or PRAG. Also are the two compatable. I plan to use the 2 oz charge cans using the A/C charging port.

When I recharge mine, I use the R134a that has the correct ration of refrigerant and oil in the can.

This is an excellent question. It has never been clear to me if you have to add oil when recharging due to a leak. Usually the topic of oil only comes up when the compressor is replaced, but a leaking A/C hose is easily spotted from the oil residue at the leak, so some oil must leak out, but maybe it's insignificant. After all, the oil is only in there to lubricate the compressor.

My advice is to post a question on the forum at
http://www.acsource.net/acforum/viewforum.php?f=1

Oil circulates throughout the system because it is miscible in R134A, particularly when the system is operating (due to the pressure). If you open your system and remove the evaporator or accumulator you will find that a few ounces of oil that has settled there, particularly in the bottom of the accumulator. You could pour it out. When refilling an intact system, one can use the cans with oil in them. In the can the oil also will be mixed in with the gas. As you state, it's impossible to know how much oil has left due to an ongoing leak. When evacuating and refilling a system that has been opened, you can add a measured amount of oil to the evaporator and/or accumulator (and the compressor if it has been dismounted or moved) before sealing the system, then evacuate, then charge with R134A without oil. In either case you are making a guess unless you have dismantled and cleaned the entire system.

There should be a sticker under the hood somewhere that tells you the oil is PAG. The POE and PAG oils should not be mixed.