AC Oil - Ester
 

In order to change a leaking hose on my AC, I need to drain, install the new hose, evac, and refill with R12. The oil in the York compressor is Ester mineral, but I have only been able to find synthetic Ester oil. (I can't imagine the 2 can be mixed).

Does anyone know where I can find mineral Ester oil?

Or: If I drain all the mineral Ester from Yorkie, would all seals need replacement for replacing the mineral with synthetic Ester oil?
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Are the 2 types indeed incompatible? The reason I ask is that motor oils surely come in "blends" which are neither all-dino or all-synthetic. I don't see why A/C oil would be any different. Maybe I'm wrong...

Drain the mineral and use the synthetic. More importantly, once you have the AC system open, replace every o-ring you can in the system!! I bought a $25 box of green Viton o-rings at Autozone and with some silicone grease (from a scuba shop) on them, replace 15 o-rings in my '87 560SEC. I found two split ones in the compressor that caused my leak, two in one fitting, one pinched (damaged) o-ring, and several that were hard as a rock. It was worth the effort!!

Also, don't overdo the ester oil in the system. The manual for my car said 300cc of oil and with that much in there it would not cool.

I have to guess "no." The oil I have found is 100% synthetic and the oil in the compressor is 19 year-old mineral oil.

What you should do is to break all lines and flush the complete system to remove the old oil. THEN you can put the correct amount of synthetic, distributed among the components. You then have a clean system with the KNOWN correct volume of oil in place.

BTW, I would be hesitant to use the Scuba shop oil. Reactions with unknown substances within a closed refrigeration system can sometimes create acids that will eat up components from the inside out. There is an inexpensive product called Nylog that is specifically designed for assembly of O-rings in refrigeration systems.

I just use PAG oil to lube. I have an old bottle that I don't use since it's hygroscopic. You're only lubing them so they seat properly without pinching. The oil will eventually wear off or dry up.