What is the function of a thermal expansion valve in HVAC systems?

The function of a thermal expansion valve in HVAC systems is primarily to control the flow of refrigerant into the evaporator. This is crucial for the efficient operation of the cooling cycle. The thermal expansion valve regulates the amount of refrigerant that enters the evaporator based on the cooling load requirements.

As the evaporator absorbs heat from the environment, the thermal expansion valve adjusts the flow of refrigerant to ensure that the evaporator operates within optimal conditions. This regulation helps maintain the correct pressure and temperature of the refrigerant, allowing it to efficiently absorb heat and ensure the system's overall efficiency. If too much refrigerant were to enter the evaporator, it could lead to flooding and reduced cooling performance; conversely, too little refrigerant would result in inadequate cooling and potentially cause the system to freeze up.

The other functions mentioned do not pertain to the role of a thermal expansion valve. Raising the temperature of the refrigerant is not its function, as the valve primarily allows the refrigerant to expand and drop in pressure when entering the evaporator. Regulating airflow within ducts and filtering dust and pollutants are handled by different components of the HVAC system, such as fans and air filters, respectively.