Air or noncondensable gas is removed from a refrigeration system by a （）

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

单项选择题What is the purpose of sub cooling R-12 in the condenser?（）

A.to increase the system efficiency by sensible heat transfer
B.to stop the liquid from flashing
C.to reduce the load on the compressor
D.to remove latent heat of vaporization and the suction piping transfer

单项选择题In terms of pressure and temperature in the refrigerant in the compressor, what happens to the primary?（）

A.its pressure and temperature are both lowered
B.its pressure and temperature are both raised
C.its pressure is lowered and its temperature is raised
D.its pressure is raised and its temperature is lowered