If you notice ice forming on the refrigerant lines of your air conditioning unit, or on the sheet metal around your evaporator, then something is not right. Typically you'll also notice that the air from the vents is not as cold as it should be. You should shut the system off and you can do some checking on your own before calling a pro.
Icing of the evaporator coils can be due to restricted airflow for various reasons, a control board gone bad, or low refrigerant levels due to a leak. That last item will require a pro to diagnose, but a homeowner can certainly check for other issues first. In this video I'll show you how to clean your evaporator coils and check other basic functions before you hire a pro.
Other videos referenced:
https://youtu.be/r_XcV2izEuo Clean And Inspect Your AC Condenser
https://youtu.be/RIJcsjJ4hAM Maintain Your Condensate Pump