单项选择题
Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）
A.Thermal expansion valve frozen open B.Suction gas heat exchanger bypassed C.Condenser clogged or fouled D.High pressure cutout switch inoperative
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 （）.
单项选择题 The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
