单项选择题
A.protect the compressor from liquid flood back
B.protect the compressor from low discharge pressure
C.start and stop the compressor upon system demand
D.start the compressor after a drop in the evaporator pressure
单项选择题 A pressure drop in the liquid line of a refrigeration system may cause（）
单项选择题 In a direct expansion type multi-box refrigeration system, the compressor is set up to cycle on and off by the（）
单项选择题 The pressure range between the system cut in and cut out pressures in a refrigeration unit is known as（）