A decrease in superheat causes the TXV to

A decrease in superheat causes the TXV to

• A. Open wider
• B. Move toward maximum flow
• C. Close
• D. Hold its position

Answer: (C)

The main idea is that the thermostatic expansion valve (TXV) regulates refrigerant flow to keep the evaporator superheat at the set point. When the superheat at the evaporator exit drops below that set point, the sensing bulb cools and signals the valve to reduce flow. By closing, the TXV decreases the amount of liquid refrigerant entering the evaporator, which raises the vapor’s departure temperature and brings superheat back up toward the desired value. If the valve were to open wider or move toward maximum flow, more liquid would flood the evaporator and further reduce superheat, which isn’t what you want. Holding its position wouldn’t correct the undershoot either. So the correct action is to close.

The main idea is that the thermostatic expansion valve (TXV) regulates refrigerant flow to keep the evaporator superheat at the set point. When the superheat at the evaporator exit drops below that set point, the sensing bulb cools and signals the valve to reduce flow. By closing, the TXV decreases the amount of liquid refrigerant entering the evaporator, which raises the vapor’s departure temperature and brings superheat back up toward the desired value. If the valve were to open wider or move toward maximum flow, more liquid would flood the evaporator and further reduce superheat, which isn’t what you want. Holding its position wouldn’t correct the undershoot either. So the correct action is to close.