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單項(xiàng)選擇題

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

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單項(xiàng)選擇題

The usual symptoms of cavitation in a centrifugal pump is （）.

A.noise and vibration
B.an increase in discharge pressure
C.an increase in suction pressure
D.lifting of the relief valve

單項(xiàng)選擇題

One cause of high head pressure occurring in a refrigeration system can be （）.

A.insufficient cooling water flow to the condenser
B.a low refrigerant charge in the system
C.the liquid valve is open too much
D.high evaporator superheat