I really wanted to add 2 oz of oil (per proair) but the shop said no need. I read somewhere here that the brand new denso compressor comes with the appropriate amount of oil for the entire system.
Im surprised but, then again Im not at the shop telling you there's no need. As
@flintknapper had stated, you need a balance. Most AC systems run around with low oil and all the owner knows is, his went out at 45k where his neighbors went 100k or more. Beside lubing the compressor, the oil coming in the low side cools the compressor. If you ever ran a 2 stroke motor, imagine running with less premix.
As for the "myth" of a compressor coming with a full charge. The modern compressors (after the 80's) don't have an oil sump. That means nowhere to store oil other than all over inside it. On some of the larger orifice tube systems you can have 12-14 ounce of oil and that same compressor on a lesser system holding 8 ounces. Also think hydroloc (spelling?).
Compressors can come with around 2 ounces (ish). I had been told that years ago.
There's a general rule for systems. Almost all compressors take 2 ounce, evap 2 ounce, condensers 1-ounce, lines depend on how long they are. Accumulators and driers are storage tanks, more so accumulator. Accumulator 3-5, driers 1-2. If you add up the "recomended" amounts, you can figure how much the lines need.
You cant forget the small amount of oil that gets removed every time you recover/evac as well as the oil that breaks down over time.
One of the issues I've faced with auto ac is quite a bit of the procedures and some of the data was never updated (think since the 70's).
Ive spent decades working with this stuff and just now I'm seeing the auto manufactures come around. It's tough when I have my students do research and they come up with conflicting info. The industrial ac on the other hand is up to spec as far as Ive seen (only spent a little time there).
Scott