🔍 Key Concepts

• Thermal expansion valve (TXV) purpose: how it controls refrigerant flow based on superheat at the evaporator outlet • What changes (pressure, temperature, superheat) when the compressor stops and refrigerant circulation slows or stops • The role of the diaphragm and sensing bulb in positioning the TXV needle

💭 Think About

• Think about what pressure conditions exist on both sides of the TXV when the compressor is not running—does the evaporator pressure stay low, rise, or equalize? • Consider whether the TXV is a simple on/off valve or a modulating valve that responds to changing forces on the diaphragm. • Ask yourself: when the compressor is off, does the sensing bulb suddenly lose temperature/pressure, or does it gradually change as the system pressures equalize?

✅ Before You Answer

• Verify that a TXV operates on balance of forces: bulb pressure vs. evaporator pressure vs. spring pressure. • Check whether a TXV is designed to snap fully open or fully closed, or to modulate position according to conditions. • Confirm whether the presence or absence of a pump-down cycle actually changes the basic operating principle of the TXV itself.