Air-Conditioning for the most part is broken down to (3) basic types.
The first two types of systems are installed by HVAC companies. Commonly referred to as central air conditioning. These systems comprise of a coil or heat exchanger, a condensing unit and linesets. The coil or heat exchanger is a unit that sits ontop of or next to your furnace. The condensing unit is placed outside next to your house on a pad. Linesets are the copper insulated lines connecting from your outside condensing unit to the furnace or heat exchanger inside your home. Linesets are also referred to as refrigeration lines, for the main reason they carry the refrigerant to the units for air-conditioning.
Forced Hot Air Systems
All forced hot air systems (FHA) have the option to include air-conditioning either during the initial installation of the heating system or as an "add-on" option later. The add on option can be done in a year or many years later, all depending when you want the central air conditioning inside your home.
During an initial installation, majority of people have the coil or air handler installed first along with their furnace. The coil is attached to the furnace, while an air handler is a unit standing by itself near the furnace. The linesets and condenser are added later, especially if you are upgrading during the off-season or winter months. In the springtime, the linsets and the condensing unit are installed and the initial "start-up" of the whole air-conditioning system is performed.
Ductless Split System
This system is installed for those of us who have heating systems other than forced hot air like forced hot water or electric heating. There is a condensing unit, linesets and a framed in unit for the air flow. The same components exist as for the forced hot air or "add-on" system, but you need a unit that is usually framed into the wall, ceiling or floor for the cool air to air condition your home. There is also a control unit to operate the aiar-conditioning system, since it is not attached to your heating system.
This of course is the oldest style of air-conditioning and easiest to install. Any homeowner can do this installation, provided they can lift the unit, which is sometimes heavy and awkward in size. The unit slides into your window resting on the bottom of the window frame with the window sliding down to hold it in place. Usually the air conditioning window unit comes with expandable sides and foam that attach to the unit to help block outside air and help secure the unit to your window frame. All you need to do is plug the cord into the nearest outlet and set the controls. Some people keep their window units installed all year long. It can be used for static cling during the winter months. Others just cover the outside of the unit with winter covers that can be bought at any hardware store and insulate around the unit for the cold air during the winter.