Which of the listed statements is a characteristic of the liquid charged power element used with thermostatic expansion valves?（）
At the designed operating temperature, the liquid refrigerant charge has changed to a vapor
B. The liquid refrigerant tends to collect at the bellows or diaphragm and reduces the valve sensitivity
C. The sensing bulb is empty of liquid refrigerant charge at the designed operating temperature
D. The sensing bulb is never emptied of liquid refrigerant under normal operating conditio
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