During the cooling cycle, hot air from the room is passed over the cold evaporator coil inside, filtered, cooled, and dehumidified, then recirculated back into the room. Cooling takes place because the refrigerant evaporates and absorbs heat through the coil. The refrigerant gas, together with the heat it has absorbed from the air in the room, is then pumped to the condenser coil outside, where it is able to reject its heat to the outside air as the refrigerant gas condenses to a liquid. The refrigerant is then pumped back again to the evaporator coil inside to recommence the cooling process.

Refrigerated air conditioning provides five basic functions:

1. Cooling

The air conditioner contains a refrigeration system that is as effective as a modern refrigerator. Most are fitted with a thermostat which controls the air conditioner automatically to maintain a constant level of comfort.

2. Dehumidifying

Excess moisture is automatically removed from the air as it is cooled. On a humid day, it is possible for a typical room air conditioner to remove up to a litre of moisture per hour from an average-sized room. This moisture is disposed of outside the building through a pipe.

3. Air circulation

The air conditioner usually contains a multi-speed fan which circulates the air to every part of the room. High fan speeds are used for fast circulation and quick cooling, while lower speeds are used to maintain levels of comfort. Even on high speeds, draughts can be controlled by movable louvers. Most allow the air to be directed up or to the right or left, while other units actually adjust air direction automatically. Some models can also draw in fresh outside air up to 10 per cent of their fan capacity.

4. Filtering

All units have a permanent filter which cleans the air as it moves through the machine. The filter can be easily removed for vacuuming or washing purposes.

5. Heating (Reverse-cycle units only)

Pressing the "heat" button activates a valve which reverses the direction of the refrigerant flow, and reverses the functions performed by the two coils. The coil in the room now becomes the condenser coil giving off heat which has been absorbed from the outside air by the external evaporator coil. The whole process operates in the same way as for cooling, but in reverse. Except for on very cold days, there is sufficient heat available in the outside air to heat the inside of the room