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單項選擇題

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

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單項選擇題

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

單項選擇題

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

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