Central home air conditioner service systems consist of two major components: a condensing unit that sits outside your house, and the evaporator coil (often referred to as an A-coil) that sits in the plenum of your furnace or air handler. The refrigerant in the A-coil picks up the heat from your home and moves it to the outdoor condensing unit. The condensing unit fan blows outside air through the condensing coil to remove the heat. The condensing unit houses the three parts replaceable by a DIYer: the contactor, the start/run capacitor(s) and the condenser fan motor. The condensing unit also houses the compressor, but only a pro can replace that. The A-coil has no parts that can be serviced by a DIYer.
1) Change your filter. The simplest and most effective way to keep your AC running smoothly is changing your filter once a month. By regularly changing your filter, you reduce a lot of the burden on your system. A dirty or clogged filter makes your air conditioner work much harder than does a clean filter. Changing your filters regularly is easy on your budget and easy on your system as well. It will lower your utility bill and extend the life of your AC.