Below is a simple description of how a refrigeration system works. The diagram will assist in further understanding this process.

The compressor, which is the first of the four main components, could be called the heart or pump of the refrigeration system. This pump pumps refrigerant gas at a very high temperature and pressure through the balance of the different components namely the condenser coil, a metering device and the evaporator coil.

Freon gas is pumped through these components within the sealed circuit of copper piping (or other), initially at high pressure and high temperature. As the Freon passes through the Condenser, the temperature of the Freon - or hot gas - is reduced by means of heat exchange, or air movement, over the condenser coil. The state of the gas within this coil thus changes from a gas to a liquid.

The metering device causes a low pressure environment to be introduced in the circuit immediately after this component. Whilst moving into this low pressure environment, the Freon gas changes its state from a liquid to a vapour. As the Freon gas changes its state to a vapour, it cools significantly via evaporation within the reduced pressure environment, which in turn offers the exceptional cooling capability of the Freon gas being used. Tthis extremely cold vaporised gas is captured within the sealed refrigerant circuit.

How can this very cold energy or vaporised gas that is contained within the piping/circuit of the refrigeration cycle be used to cool an external environment such as a bedroom or office?

Once again by means of heat transfer, the cooling ability of the vaporised Freon gas is then transferred externally. This heat transfer (cooling in this case) from the surface of the refrigerant pipes is transferred to the air moving over these pipes. In an air conditioning unit this heat transfer is increased dramatically by introducing large volumes of air over the surface area of the evaporator. This is normally done mechanically by a ventilation fan. The cold air is contained and blown into the area to be cooled by means of specially designed ducting or housing.

Both the condenser coil and evaporator coil are designed in a similar way to a car radiator coil arrangement. This design allows for a large volume of air to be passed over a long section of piping, which is coiled in such a way so as to take up a small area. The design of this coil must also ensure that the maximum surface area is in the path of the air moving over this coil, thereby ensuring a good result.

To understand this question you will have to take note of the diagram above. An air conditioning unit is made up using all the components as described above and more.

Most reverse cycle air conditioning units installed are the split type unit, either wall mounted or ceiling mounted. These split units are divided into two units, hence the terminology split unit. These two units, the fan coil (inside unit) and the condenser (outside unit) are inter-connected by copper piping.
A brief description of each unit will help answer this question:

1. Condenser unit (external unit)

This unit is normally mounted at ground level on the outside of the building. It contains a number of mechanical and electrical components, including the compressor, the condenser coil, fan/s and a valve called a three way valve. It is this valve that causes a reversing of the refrigerant cycle, when the heating mode on the thermostat is selected, thereby introducing warm air to the inside of the building and cold air to the outside.
Thus the refrigeration cycle allows for excellent heating and cooling results.

2. Fan coil unit (indoor unit)

This unit can be installed on the wall inside a building, or in the ceiling void. The housing of this unit contains a number of working parts including the evaporator coil and fan. The position of this unit is dependant on the model and type selected depending on the special capabilities that each model offers.