NATE Air Conditioning and Heat Pumps Practice Exam

What is the primary function performed by a thermal expansion valve?

1. It maintains the correct superheat in the hot vapor leaving the compressor

2. It maintains the correct superheat in the suction vapor leaving the evaporator

3. It maintains the proper subcooling level in the liquid refrigerant

4. It prevents flash vapor bubbles from developing in refrigerant entering the evaporator

The correct answer is: It maintains the correct superheat in the suction vapor leaving the evaporator

The primary function of a thermal expansion valve is to maintain the correct superheat in the suction vapor leaving the evaporator. The superheat refers to the temperature of a vapor above its boiling point at a given pressure. By ensuring the proper level of superheat, the thermal expansion valve helps to protect the compressor from potential liquid slugging, which can occur if liquid refrigerant reaches the compressor instead of vapor. In operation, the thermal expansion valve regulates the flow of refrigerant into the evaporator based on the pressure and temperature of the refrigerant exiting the evaporator. This function is crucial as it ensures that the evaporator operates efficiently, absorbing the maximum amount of heat and providing optimal cooling performance. The other choices relate to different aspects of refrigerant management but do not accurately describe the primary operation of the thermal expansion valve. The focus on superheat maintenance in the suction line is what clearly defines the role of this component within the refrigeration cycle.