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

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單項(xiàng)選擇題

The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.

A.dead band action
B.neutral zone action
C.range
D.on-off action

單項(xiàng)選擇題

Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.

A.cavitation
B.electrolysis
C.abrasion
D.corrosion