单项选择题

If a refrigeration compressor is running continuously without lowering temperature as normal in the refrigerator, the trouble may be （）.

A.excessive condenser cooling water
B.warm food in the refrigerator
C.a shortage of refrigerant
D.s shortage of compressor oil

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单项选择题

Thermostatic expansion valve are （）.

A.either all the way open or all the way closed
B.normally open
C.throttled depending on load
D.controlled by suction pressure

单项选择题

When a hydraulic vane pump is working, which of the following is in contact with the vanes?（）
(1) the rotor
(2) the internal surface of the housing
(3) the external surface of the housing

A.(1) only
B.(2) only
C.(1) and (2)
D.(1), (2) and (3)

单项选择题

Which of the following items is necessary for all waste heat boiler installations, regardless of design or manufacturer? （）

A.Control of evaporation
B.A separate means to prevent feed-water contamination
C.Power circulating pump
D.Super-heater