dr bob

If you are going with R12 and never anticipate changing to R134a, use mineral oil. Else use POE. The mineral oil is less hygroscopic than POE, so will allow the drier to capture moisture better than it might with POE. The effective difference is negligible though if you use care and let your vacuum pump "boil out" any moisture that condensed in the system prior to adding oil and refrigerant.

Adding oil: The compressor gets drained and flushed a couple times with the new oil prior to installation. After the last "drain", refill with the correct amount for your compressor, then immediately put the compressor in and connect the hoses, and get the vacuum pump running. The amount to time needed to boil all the moisdture out with the pump varies with ambient temperature. Even in SoCal with chronically warm days, I'd leave the pump running on the car overnight. To add the rest of the oil, close the valves on your charging manifold and disconnect the hose from the vacuum pump. Dip the hose in the measuring cup holding the rest of the oil charge, and open the high-side (red) valve on the manifold, The vacuum in the system will cause the oil to be drawn in at the drier and the downstream end of the condenser, and avoids the suction side of the compressor. As soon as the oil is in, close the valve to minimize air contamination. Reconnect the vacuum pump, start it and slowly open the low pressure valve on the charging manifold. Run it for at least 15 minutes or until the system pressure is lowest again. Now charge the system with liquid by weight into the high-side port, with engine off and everything still cold. The liquid will wash any remaining oil from the manifold and the high-side hose, and will flow out through the drier and the condenser, evaporating along the way. Once the correct amount of refrigerant is in the system, let the system sit for a few minutes before you start the car. Prior to the first use following a liquid charge, I spin the compressor by hand a few times to make sure there isn't a slug of liquid in a compressor cylinder. Then start the car and check pressures and temperatures to verify your work.

Using POE makes sense if you ever anticipate having R134a in the system. Whatever oil you use in the system will saturate the dessicant in the drier, and coat the walls of the hoses and heat exchangers (condenser and evaporator). Short of a solvent flush, there's no good way to get all the old oil out of the system. Using POE now means that you can do a "flying" refrigerant change to R134a by simply evacuating the R12 out, recharging with R134a. Note that PAG is not compatible at all with R12; the system depends on the oil being miscible in the refrigerant vapor flow. PAG in R12 doesn't carry in the vapor, so very quickly it starves the compressor of lubrication. POE is miscible in both R12 and R134a, so is in my experience the best choice for any converted system.

545svk

Thanks for this - One question, do you fill each component separately or does the oil distribute "naturally" with use?
Thanks

griffiths

The refrigerant oil will spread out through the system as it is carried by the refrigerant.

https://griffiths.com/ac-system-help.../r134a-vs-r12/

dr bob

Just be careful to clear the compressor cylinders manually before you run the compressor the first time. This is particularly important if you put ALL the oil in the compressor before you install it. Many compressor instructions call for this anyway. At manual-turning speed, the reed valves open far enough and fast enough to avoid hydraulic damage as the compressor tries to pump an oil slug. Any oil slug in the inlet manifold or cylinders ends up safely in the discharge manifold. Failure to do this simple step risks piston and reed valve damage. Folks who have worked on GM R4-style compressor systems may be most familiar with the consequences of oil in the cylinders. The warning applies to all piston compressor systems.

griffiths

Turn the outer clutch hub in the same rotation of the crank pulley 12 times.