I used to be an HVAC contractor before I became a real estate investor. For the most part, I agree with what Jenni Utz said. For the standard residential system changing the filters regularly and cleaning the condenser/outside unit coil surfaces and fan blade regularly is probably all you need to do. The evaporator/inside coil can get clogged too, but changing the filter regularly eliminates that problem. Restricted air flow across those surfaces increases energy consumption and puts unnecessary stress on the moving parts.
However, A/C systems are sealed systems and should not have to topped up or recharged unless there is a leak. Also, for more modern systems (talking the last 15 -20 years) all have permanently oiled bearings that take a very long time to wear out. Of course, as the years go by, rotating parts should be looked at more frequently. There are other small parts such as relays and capacitors that can and will go out, but those should be replaced as they fail.