The low pressure side of a refrigeration system is considered to exist from the （）.

单项选择题If the electric motor driving an air compressor fails to start, the cause may be a （）.

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 （）.

A.superheated
B.saturated
C.dense
D.flooded

单项选择题The vacuum maintained in the salt water feed heater shell of a flash-type evaporator is generally accomplished by （）.

A.a separate air ejector unit
B.a direct unimpeded connection between second stage and salt water feed heater
C.either by vacuum drag or an external line from the first stage via a fixed orifice
D.the fixed orifice provided in the steam supply line

单项选择题In which of the listed refrigeration system components does superheating of the refrigerant take place?（）

A.Expansion valve
B.Evaporator
C.Drier
D.Receiver

单项选择题Excessive lube oil consumption by a reciprocating air compressor can be caused by （）.

A.using a slightly dirty air filter
B.using oil having an excessive viscosity
C.intercooler or after-cooler leaks
D.carrying the oil level higher than normal