Kestas is offering some valuable wisdom here!

An a/c system is a great place to apply the old term "if it ain't broke, don't fix it.

Every time you break open the system, you risk introducing moisture. Moisture combined with refrigerant creates an acid that will eventually eat its way out of the system. I have seen systems on centrifuges, scintillation counters and other scientific instrumentation units that once serviced started giving frequent trouble.

When a system ceases to produce cool air it is then time to give it the attention it deserves. If you are lucky, your system will have a one ounce per year leak causing a need for recharge after 15 or 20 years. If you are not lucky you will have a "sure enough" leak sooner than that. At that time, you fix the leak, probably replace the filter drier, thoroughly evacuate and recharge. Until then "don't mess with it!"

This is the only subsystem of your car with lubricant in which you should NOT Change oil hot and change oil often.

Good luck,