Finally had time to do the replacement.
Getting at the compressor/clutch assemble was easy requiring both below and above activity ... almost a relief to be able to replace on that is simply bolted on with four long bolts firmly connecting the compressor to the block, instead of the previous styles requiring rotation for tensioning the compressor.
Most exasperating was the lack clearance for getting a couple of the bolts out ... finally managed to move other hoses and lines out the way enough to do so.
Took about 2 hours (could shorten to about 30 minutes if I had to do it again).
The new compressor came with a plate covering the inlet and outlet hose connectors to keep the compressor sealed during shipping. The o-rings that sealed the plate looked to be new, so I Nylog'd well and used them. Nice method for connecting the lines to the compressor ... reference older GM systems and god-forbid, Yorks.
I added about 4-5 ounces of synthetic compressor oil. This was a bit more than recommended by some and less than recommended by some. The old compressor had almost no oil in it ... likely in the lines, I assumed, so reasoned I would use a bit less ... would love to hear more on this topic as there appears to be quite a bit of latitude in the quantity of the oil.
Replaced the receiver-dryer and Nylog'd threads and o-rings ... seemed to go together quite easily, including R&R of the switches.
This part took another hour or so ... could shorten to about 15 minutes if had to do it again.
Pulled vacuum on the system with a new MasterCool pump (I had always wanted one, but lacked "rationalization"). I recall replacing a compressor 20 years ago and using an old converted vacuum pump at a military hobby shop that took 45 minutes to pull a poor vacuum ... even though this was the smallest model available, it took about 3 minutes ...let it run for 20 minutes and pulled 31.5" (gauge error?) on the low side ... connected up high side and pulled it to what could be estimated to be about 30" below zero (no negative shown on the high side gauge).
I do need some help with technical questions:
1. How long should the pump run once the vacuum stabilizes?
2. How much vacuum loss should there be over what period of time? (looks like a I lost about 1 inch over 18 hours)
3. Should both high and low side be evacuated or just low side?
4. Can I leave system evacuated, but without R-12 until Spring?
5. When I charge the system, I was going to hook up low and high with gauge set and slowly add two pounds ... what should pressures be for this system as I add further?
Hope this helps anyone else considering doing this - not a hard job ... it is small compensation for the wonderful technical assistance I have received on this site.
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg