The indoor unit/Air Handler
Includes the filter, the air handler and the evaporator coil. The air handler blows filtered air through the evaporator coil. The evaporator coil is kept cold by the circulation of a refrigerant. Air that travels across the evaporator coil gives up heat (the colder coil absorbs it) and humidity (moisture condenses upon contact with the cold surface of the coil). The cooler, drier air that continues through the air ducts is vented throughout your home to maintain your desired comfort level. Depending on the structure of your home, the duct work may be above the ceiling or below the floor.
The Heat Pump/condensing unit
Heat pumps work by switching the flow of refrigerant ( reverse cycle) moving existing heat from one area to another. The condenser absorbs heat from the outdoor air (even the coldest air contains some heat) and transfers it to an indoor air handler inside the home. Indoor air is warmed in the heat exchanger and circulated throughout the home. During the summer, the process is reversed to cool and dehumidify the home. One advantage of a heat pump is that it provides both heating and cooling capabilities in one unit. Electric heat pumps are usually supplemented with a backup system, such as Electric Heat Strips, in case of extended periods of extreme cold temperatures.