单选题Insufficient refrigerant in a refrigeration plant may result in （）.A high discharge pressureB frosting of the crankcaseC high temperature of the overboard waterD low suction pressure of compressor

If a refrigeration system were short of refrigerant, the condition would result in

A.continuous running of the compressor

B.high suction pressure

C.high discharge pressure

D.short cycling of the compressor on the water failure switch

Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?

A.A shortage of liquid refrigerant.

B.Excessive frost on the evaporator.

C.Excessive condenser cooling water.

D.Insufficient condenser cooling water flow.

If the refrigeration compressor crankcase is sweating, the cause may be due to

A.a shortage of refrigerant

B.the compressor running continuously

C.liquid refrigerant returning to the compressor

D.the compressor short cycling on the high pressure cutout

A firebox explosion in an automatically fired auxiliary boiler may be the result of ______.

A.excessive purging before lighting off

B.insufficient trail for ignition period

C.a faulty transformer in the ignition circuit

D.insufficient purging before lighting off

Sweating of the refrigeration system compressor crankcase is caused by_______ .

A.too much superheat

B.insufficient superheat

C.suction pressure too low

D.excessive refrigerant returning to the compressor

Sludge may be formed in the oil in the crankcase of a reciprocating air conditioning compressor as a result of ______.

A.refrigerant bubbles in the lube oil

B.refrigerant reducing the lube oil viscosity

C.oxidation(氧化) of the lube oil from overheating

D.reducing the floc or cloud point of the oil

Low compressor head pressure in a refrigeration system can be caused by ___.

A.insufficient condenser cooling water

B.excessive condenser cooling water

C.air in the refrigeration system

D.excessive refrigerant in the system