Once a year you should get your HVAC serviced.
For me, I do a twice a year cleaning.
I get the AC portion focused on in spring and the heating method in the fall. I have a central heating and cooling unit though. So it is one system that gets the maintenance on it. But for cooling, I get new refrigerant and the fan blades checked. For heating it is all about the dust in the system. I really like getting the twice a year cleaning to ensure my air quality is fresh. I also want to remove all the hair that gets in my system. I have really long hair and I shed worse than any dog. I have to clean my dryer lint trap constantly. My tub drain needs to be snaked bi-weekly. I also vacuum and sweep to get the hair off my floors. An air filter should be able to last in a system for around four weeks. With my long hair, two to three weeks is about all it can take. So I figure that normal people go a year with one cleaning, I do two cleanings to get my hair removed from it. The air filter doesn’t stop everything from getting in the system. I don’t want to have my long hair ruining parts in the HVAC. I also get ductwork cleaning way more than any normal homeowner does as well. I don’t want dust, debris and again, my hair clogging up the air ducts. The idea of breathing in my old, dusty hair sounds disgusting.