Vapor bubbles present in the liquid upon arrival to the thermal expansion valve in a refrigeration system may cause erosion of the expansion valve's needle and seat. This, in turn, could cause what condition?
• Thermal expansion valve (TXV) function – how the needle and seat control refrigerant flow into the evaporator • Erosion or wear of the needle and seat – what happens when the valve can no longer seal properly • Relationship between valve sealing, refrigerant flow, and system temperature/pressure behavior
• If the needle and seat are eroded, will the valve tend to leak more refrigerant through or block refrigerant more than it should? Think about which direction erosion pushes the behavior. • How would continuous leaking versus tight sealing affect evaporator temperature and pressure over time? Which choice best matches that condition? • Which of the listed conditions suggests the valve is stuck in a more-open position, and which suggests unstable control or cycling around the setpoint?
• Clarify what "freezing open" vs "freezing shut" would look like in terms of refrigerant flow and evaporator cooling. • Consider whether erosion is more likely to cause a poor seal (leakage) or a tighter closure – then match that to the options. • Make sure you can distinguish unstable modulation (hunting) from a valve that is physically stuck in one position.
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