If no gaskets are used in the piping joints of a Freon system, the joints must be（）

单项选择题If the temperature in the icebox is too high, the trouble could be（）

A.a clogged scale trap
B.air in the system
C.automatic controls not functioning properly
D.insufficient cooling water to the condenser

单项选择题Air or noncondensable gas is removed from a refrigeration system by a （）

A.separating chamber
B.system of baffles
C.purge valve
D.vacuum reducing valve

单项选择题Where are the zinc plates located?（）

A.saltwater side of the condenser
B.refrigerant side of the condenser
C.in the evaporator coils
D.in the suction strainer

单项选择题The device used for low-pressure control and high-pressure cutout on a compressor is called a（）

A.cutout
B.pressure controller
C.controller switch
D.cutout switch

单项选择题The purpose of the purge valve at the top of the condenser in a refrigerating system is to（）

A.remove any air that may accumulate in the system
B.take out unpleasant fumes from the refrigerant
C.vent off excess refrigerant in an emergency
D.permit opening the refrigerating system for cleaning and inspecting