单项选择题
Which of the conditions listed will cause a refrigeration compressor to run constantly without simultaneously decreasing the temperature in the refrigerated space?（）
A.Shortage of refrigerant oil B.Slight shortage of refrigerant C.Excessive condenser cooling water flow D.Faulty expansion valve
单项选择题 Air compressor cylinder un-loaders enable the compressor to （）.
单项选择题 The movement of heat within a fluid, caused by the application of thermal energy, is called （）.
单项选择题 A gate valve installed in a pipeline should be （）.
