I am converting my '89 740 from R12 to R134 and want to do it sort of right (minimal cost). My car has a total of only 100,000mi on it.

1) I plan to remove the compressor to empty the mineral oil and refill w/ proper oil. Is Ester or PAG the better oil to refill with for R134 (I see both mentioned).

2) Should I just rotate and turn the whole compressor (and the shaft by hand at the same time) to dump old oil, or use brake cleaner to try to flush after no more old oil pours out on its own?

3) How many ounces of oil should I add of he desired oil, and where is the best place to introduce it?

4) I want to replace all O Rings accessible under the hood. Anyone know how many of what sizes I should order? I see 1/2" and 5/8" are used?

5) To flush system I assume one just removes all hoses uses air pressure to blow out what will come out, and then blasts brake cleaner through the lines, followed by more compressed air to dry the brake cleaner from the system prior to re-assembly?

6) Upon re-assembly, I see "Nylog Blue" recommended for lubricating/sealing O-Rings prior to re-installation of hoses. I guess this is superior to lubricating w/ silicone grease? I am changing the orifice to a "R-134A" one, BTW, which I understand is better suited to the pressures of an R-134 system.

7) I understand that in conversions, one should start with 20% LESS R134 by weight than the system calls for with R12 since R134 develops higher pressures?

Other than a new Receiver/Drier, New R-134 fittings, New R-134 Orifice, New O-Rings, New R134 compatible oil, and use of "Nylog Blue," are there any parts I should replace "as a matter of course?"

My A/C has not worked for at least 10 years, but the car is now moving to AZ where A/C is a must. The compressor shaft turns freely by hand (2 fingers turns the compressor shaft smoothly). Is it unusual for the OEM compressors to need replacement at my car's age and mileage? The A/C was used summers in a temperate climate (MD) for 10 years of its life, and the system was never opened to my knowledge (car was in family since brand new), and they just stopped using A/C when it no longer cooled well (I suspect slow loss of refrigerant).

Obviously any massive leaks should show up when I attempt to pull a vacuum, but curious about experiences of the "Board" regarding how long these OEM compressors last. I'd rather spend the extra $225 for a compressor NOW than find "they all fail at 125,000mi" for instance. I know they fail in fewer miles in AZ than in WA (where seldom used), of course, so I'm just looking for guesses here. Obviously, I could have a bad condensor or evaporator, so I should look for this w/ a vacuum before opening the system at all to replace ANY parts. I'd hope few condensors/evaporators fail.

Thanks for any comments or helpful hints as this is the first I've messed w/ A/C systems (though I do have a set of gauges and a good Robbin vacuum pump) and am an otherwise experienced mechanic (aircraft and automotive).

Feel free to copy and paste my questions in your replies, or just address questions by number to save time-whatever works! All help or experiences appreciated.

Bob