HVAC Metering Devices Practice Test 2026 – Complete Exam Prep

A thermostatic expansion valve (TXV) is designed to regulate refrigerant flow into the evaporator based on the cooling needs of the system. Its primary function is to maintain the proper superheat of the refrigerant, which ensures optimal efficiency and performance of the HVAC system.

When the compressor is running, the TXV is typically operational because the system is actively transferring heat. The compressor creates a low-pressure area that allows the refrigerant to flow into the evaporator, where it absorbs heat from the environment or space being cooled. The TXV continuously adjusts the flow of refrigerant based on the temperature and pressure conditions of the evaporator, providing precise control over the cooling process. This dynamic regulation is crucial for maintaining system efficiency and preventing issues such as flooding or starvations in the evaporator.

In contrast, during system shutdown, the TXV would not be operational as there is no flow of refrigerant due to the compressor being off. While the TXV may encounter conditions of high ambient temperatures or maximum refrigerant flow, these scenarios do not guarantee that the valve will be fully operational. The primary factor that ensures the TXV is actively managing refrigerant flow is the running state of the compressor, which establishes the necessary conditions for the cooling cycle