How often should an AC be serviced, and what is included in a normal service?

Most homes service an AC once before summer and once after; heavy use needs it more often. A normal service usually means cleaning the filters, the indoor coil and the drain, and checking the outdoor unit. Gas filling, coil repair and parts are extra. Ask the technician what exactly is included and whether gas pressure checking is part of it. If they say gas is low, ask them to show the pressure reading.