单项选择题

A knocking sound emitted from an unloaded air compressor is probably caused by （）.

A.damaged intake valves
B.excessively tight mounting bolts
C.insufficient cylinder lubrication
D.a loose piston

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单项选择题

The refrigeration system low pressure cutout switch is actuated by （）.

A.an electric system manager
B.a sensing bulb at the tail coil of the evaporator
C.pressure changes in the suction line
D.failure of the king solenoid valve

单项选择题

Hydraulic machinery failures are commonly caused by contamination of the hydraulic fluid and （）.

A.fluid friction
B.fluid turbulence
C.component misalignment
D.pressure surges

单项选择题

When you adjust a thermostatic expansion valve, （）.

A.refrigerant must be bled off the sensing line before adjustments are made
B.all refrigerant must be pumped into the receiver before adjustments are made
C.time must be allowed for conditions to stabilize in the evaporator before further adjustments are made
D.all refrigerant must be routed through the dehydrator while changing the superheat setting