What role does a thermostat play in an HVAC system?

A thermostat is a crucial component of an HVAC system, as it regulates and controls the temperature settings of the system. It functions as the interface between the user and the heating or cooling system, allowing for the adjustment of the indoor climate to maintain comfort. By sensing the current temperature and comparing it to the desired setting, the thermostat sends signals to the HVAC system to either activate or deactivate heating or cooling mechanisms as needed.

This control mechanism ensures that the indoor environment remains within a set range, thus optimizing energy efficiency and comfort for the occupants. The other options provided touch on various aspects of HVAC systems, but they do not pertain to the primary function of a thermostat. For instance, adding humidity pertains to humidifiers, filtering dust and allergens relates to air filters or purifiers, and measuring refrigerant levels is a function related to the refrigerant management system within the HVAC unit.