单项选择题
Low compressor head pressure in a refrigeration system can be caused by（）.
A.insufficient condenser cooling water B.excessive condenser cooling water C.air in the refrigeration system D.excessive refrigerant in the system
单项选择题 Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）
单项选择题 The usual symptoms of cavitation in a centrifugal pump is （）.
单项选择题 One cause of high head pressure occurring in a refrigeration system can be （）.
