A knocking sound emitted from an unloaded air compressor is probably caused 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

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

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