單項選擇題Excessive circulation of the lubricating oil with the refrigerant in a refrigeration system will cause （）.

A.carbon deposits on the compressor suction valves
B.the evaporator temperature to increase
C.rapid corrosion of the thermal expansion valve
D.no operating problems


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1.單項選擇題Scale accumulation on evaporator heat exchange surfaces （）.

A.increases brine density
B.increases distillate salinity
C.reduces metal corrosion
D.reduces heat transfer

2.單項選擇題In order to properly remove air from the casing of a centrifugal pump when starting, the pump should have a （）.

A.positive head
B.negative suction head
C.mechanical seal
D.vent valve attached to the casing at the top of the volute

3.單項選擇題The valve best suited for throttling gas or liquid flow in a pipeline is the（）.

A.gate valve
B.globe valve
C.check valve
D.plug cock

4.單項選擇題Which of the listed statements is a characteristic of the liquid charged power element used with thermostatic expansion valves?（）

A.At the designed operating temperature, the liquid refrigerant charge has changed to a vapor
B.The liquid refrigerant tends to collect at the bellows or diaphragm and reduces the valve sensitivity
C.The sensing bulb is empty of liquid refrigerant charge at the designed operating temperature
D.The sensing bulb is never emptied of liquid refrigerant under normal operating conditions

5.單項選擇題Differential pressures can be measured with the use of a （）.

A.diaphragm type gage
B.pressure transducer
C.manometer
D.All of the above