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單項(xiàng)選擇題

Black smoke coming from a boiler can be caused by （）.

A.low water level
B.low oil pressure
C.excessively high fuel pressure
D.an improper air/fuel ratio

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單項(xiàng)選擇題

Which will cause the high pressure cutout to stop the compressor in a R-22 system?（）

A.Condenser leakage
B.A shortage of liquid refrigerant
C.Excessive frost on the evaporator
D.Not enough condenser cooling water

單項(xiàng)選擇題

Insufficient refrigerant in a refrigeration plant may result in （）.

A.high discharge pressure
B.frosting of the crankcase
C.high temperature of the overboard water
D.low suction pressure of compressor

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