Types of central Air conditioners
Central air conditioning systems (namely ducted split systems) are the dominant types of AC, but ductless mini-split systems and window (room) air conditioners are becoming increasingly popular.
These two last types of air conditioners are excellent alternatives to central AC, and can provide lower cooling bills. As to portable air conditioners, though increasingly popular, their effectiveness is rather questionable, and they pose venting problems.
See:
Best Air Conditioning
Window air conditioners tips
Ductless air conditioners advantages and disadvantages
Central AC Types
There are two types of central air conditioners: split-systems and packaged units; both central AC types use supply and return ducts to get air circulation.
Supply ducts carry cooled air from the AC to the home (using openings in the walls, ceilings or floors - covered by grills - technically called registers). After some time, the cooled air, circulating in the home, becomes warmer and flows back to the AC through the registers and return ducts.
Central Packaged AC type
In a packaged AC type, the different parts of the system (evaporator, condenser and compressor) are all located in the same cabinet, usually placed on a roof or next to a foundation, outdoors. This outdoor located «package» is connected to the home’s interior through supply and air return ducts.
This type of central air conditioner may involve electric heating coils (or natural gas furnaces), which may replace a separate furnace. In case you want a ducted system, and haven’t a furnace, this is the type of central AC systems to consider.
Central Ducted split-System type & furnaces and air heat pumps
If your home already has a furnace or a heat pump but no air conditioner, then an AC split-system can be a better solution than a packaged system (to reduce costs).
In AC ducted split-system the air conditioner's evaporator coil is often installed in the cabinet or main supply duct of a furnace or heat pump. In other words: this type of central air conditioner, the indoor cabinet contains a furnace or the indoor part of a heat pump...
Mini-splits (Ductless air conditioners)
Ductless split-systems are often known as "mini-splits", and shouldn't be confused with the central ducted split-system type.
When shopping, make sure the dealer understands which system you are referring to. The conventional central split AC (ducted) and the non-ducted split air-conditioners (mini-splits) are two different types of air conditioners.
Mini-splits are - on their main parts - similar to conventional central air conditioning systems, but instead of ducts they use a conduit that carries the refrigerant and the power, and they have a set of separated indoor air-handlers, one for each zone of the home to be cooled (some mini-splits can operate as heat pumps, providing both summer cooling and winter heating).
See also:
Air Conditioning Efficiency Basics
Air conditioners Alternatives
High Efficient Air Conditioners
Air Conditioners Types