HVAC thermostat controls HVAC systems in a building or structure. The device measures the temperature of the air in the controlled space and compares it against the desired temperature. As a result, the thermostat tells the HVAC system when to turn on or off based on this comparison.Thermostat HVAC Systems primary function is to control the temperature of a space. https://www.partshnc.com/hvac-controls/thermostat