單項選擇題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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1.單項選擇題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

2.單項選擇題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

3.單項選擇題Air that may enter a refrigeration plant tends to collect in the （）.

A.upper part of the receiver
B.upper part of the condenser
C.down stream end of the cooling coil
D.outlet end of the condenser

4.單項選擇題Moisture should be kept out of an R-12 system because it tends to cause （）.

A.icing of the automatic controls
B.embrittlement of some parts of the automatic controls
C.sludge in the lubricating oil
D.all of the above

5.單項選擇題Black smoke coming from a boiler can be caused by （）.

A.low water level
B.high water level
C.excessively high fuel pressure
D.low oil temperature