单选题Air entering an air-cooled refrigeration system is indicated by （）.A frosting of the liquid lineB higher than normal head pressureC a clear sight glassD abnormally cold reefer boxes

Air trapped in the hydraulic fluid of a steering system may be indicated by

A.the steering pumps overspeeding

B.a jammed open relief valve

C.a constantly occurring improper rudder response

D.excessive ram pressure

You are in a tropical port．The refrigeration machinery on a container loaded with air-cooled fruit fails．It cannot be repaired for 18 to 24 hours．Which step should you take to reduce the temperature rise and spoilage of the fruit ________．

A.Discharge a cylinder of nitrogen into the container

B.Shade the container and periodically hose it down

C.Seal any ventilation openings and add dry ice

D.Spread ice over the top layer and in any voids within the container

When adding oil to a refrigeration system, precautions must be taken to ensure that

A.the compressor suction pressure is not too high

B.all air is purged from the pump and charging fittings

C.the high pressure cutout switch is held open to prevent accidental starting

D.the condenser is completely shutdown first

In the refrigeration system, a shortage of refrigerant is indicated by

A.the compressor short cycling on high pressure cut out switch

B.high suction pressure

C.high head pressure

D.bubbles in the sight glass

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