R134a contains the necessary lubricant to keep the compressor running smoothly. That is why nobody responded to your thread. I read it 12 hours ago and thought about writing you, but I didn't have the time to explain it.
In normal use the refrigerant and oil charge should last the life of the car. If the system develops a leak or if any component of the system needs to be replaced, then the refrigerant and oil charge needs to be evacuated and then replaced.
Though you might need to replace an ounce of oil when a hose is replaced, it is generally unneeded and will last the life of the compressor. New Compressor? Then you add oil. Changing oil in the a/c system is done as often as you change the air in the tires.
Lol at gdanahar - did you mean winter or summer air in the tires - ?
The only thing you need to do to take care of your A/C is to run it at least once a week, every week (no matter the weather). Run it for a minute or two (toyota states 20 seconds is long enough). The reason you must run it is to circulate the refrigerant oil to the bearings and seals inside the compressor. If you dont run the air often enough, these parts dont get oil, dry out, sieze up next time you turn on the air, maybe snap your drive belt, and then cost you lots of money to fix.