The main purpose of the air-conditioning system is to create comfort conditions by controlling the temperature, humidity and flow of air inside the rooms. To provide the comfort conditions throughout the year, the air-conditioning systems are fitted with three controls: temperature controls, humidistats and airstats that control the temperature, relative humidity and flow of air inside the room respectively. Let us see all these in more details.

The temperature control devices maintain the proper temperature inside the room as per our comfort requirements. When the desired temperature is reached these devices switch off the compressor of the air-conditioning system and when temperature goes away to certain extent from the desired levels the compressor is restarted. The setting of the temperature is done by the user manually or automatically using the remote control devise of the air-conditioning system.

One of the most commonly used devise for controlling the room temperature is the room thermostat. It senses the temperature inside the room and causes the electrical contacts to the compressor open or close depending on the temperature inside the room. There are various types of thermostats, but the most commonly used is the bimetal room thermostat. It comprises of two metals which at particular temperature are of same length, but when their temperature is increased one metal increases in length more while the other increases less due to their different coefficients of expansions. When the bimetal is heated it tends to get bent which helps in opening or closing of the electrical supply to the compressor.