单项选择题
A.leaking unloader
B.tripped circuit breaker
C.control line leak
D.defective pop valve
单项选择题 The refrigerant gas returning to the compressor should be （）.
单项选择题 The vacuum maintained in the salt water feed heater shell of a flash-type evaporator is generally accomplished by （）.
单项选择题 In which of the listed refrigeration system components does superheating of the refrigerant take place?（）