A contactor is a $25 mechanical relay that uses low-voltage power from the thermostat to switch 220-volt high-amperage current to the compressor and condenser fan. AC contactors can wear out and are at the top of the list of common air conditioning service failures. Even if your contactor is working, it pays to replace it every five years or so. Unscrew the old contactor before removing the wires. Then move the wires to the new unit (photo 6).
You should also have air ducts cleaned after recent water contamination or water damage to prevent mold; after renovations or remodeling to ensure debris and dust didn’t settle in the vents and ducts; if you are having problems with allergies or asthma; or when you are moving into a newly purchased home, especially if the previous owners smoked or had pets. The National Air Duct Cleaners Association (NADCA) recommends getting your air ducts cleaned every three to five years, or every two to three years in regions where homeowners use their air conditioning and heater for many months of the year, while the EPA suggests homeowners have duct cleaning done as needed.
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.