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.
If your compressor doesn’t have an overload button and you hear it humming or buzzing, poke a screwdriver or stick down through the top grille and try to spin the fan blades clockwise. If doing this gives the fan enough of a boost to get it going, the unit has a faulty capacitor that must be replaced. See How to Test and Replace an AC Run Capacitor, above.

The compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car radiator or typical household air conditioner does. Such a system dehumidifies the air as it cools it. It collects water condensed from the cooled air and produces hot air which must be vented outside the cooled area; doing so transfers heat from the air in the cooled area to the outside air.

In addition to the information below, see these two articles for the general care and maintenance of your air conditioner: Preparing Your Air Conditioner for Summer and How to Replace Furnace & AC Filters. Most noteworthy, you should replace the filters at least twice a year, before the heating and cooling seasons. For information on furnace problems, please see Furnace Not Working.
Absorption refrigerator Air barrier Air conditioning Antifreeze Automobile air conditioning Autonomous building Building insulation materials Central heating Central solar heating Chilled beam Chilled water Constant air volume (CAV) Coolant Dedicated outdoor air system (DOAS) Deep water source cooling Demand-controlled ventilation (DCV) Displacement ventilation District cooling District heating Electric heating Energy recovery ventilation (ERV) Firestop Forced-air Forced-air gas Free cooling Heat recovery ventilation (HRV) Hybrid heat Hydronics HVAC Ice storage air conditioning Kitchen ventilation Mixed-mode ventilation Microgeneration Natural ventilation Passive cooling Passive house Radiant heating and cooling system Radiant cooling Radiant heating Radon mitigation Refrigeration Renewable heat Room air distribution Solar air heat Solar combisystem Solar cooling Solar heating Thermal insulation Underfloor air distribution Underfloor heating Vapor barrier Vapor-compression refrigeration (VCRS) Variable air volume (VAV) Variable refrigerant flow (VRF) Ventilation

An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which have thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[17]

Air conditioning is common in the US, with 88% of new single-family homes constructed in 2011 including air conditioning, ranging from 99% in the South to 62% in the West.[50] In Canada, air conditioning use varies by province. In 2013, 55% of Canadian households reported having an air conditioner, with high use in Manitoba (80%), Ontario (78%), Saskatchewan (67%), and Quebec (54%) and lower use in Prince Edward Island (23%), British Columbia (21%), and Newfoundland and Labrador (9%).[51] In Europe, home air conditioning is generally less common. Southern European countries such as Greece have seen a wide proliferation of home air-conditioning units in recent years.[52] In another southern European country, Malta, it is estimated that around 55% of households have an air conditioner installed.[53] In India AC sales have dropped by 40%[clarification needed] due to higher costs and stricter energy efficiency regulations.[54]
When your furnace needs immediate repair, trust the professionals at BGE HOME. We understand that furnace problems are more than a mere inconvenience – they can have a serious impact on the health and safety of you and your family. Our technicians are available 24-hours a day for emergency repairs. Click to schedule your repair and have peace-of-mind knowing that a licensed, certified HVAC technician will have your system up and running as quickly as possible. For 24-hour emergency furnace repair service, call 1-888-243-4663.