单项选择题
A.loose expansion valve control bulb
B.low differential setting on the H-Pcutout
C.blown fuse in the motor circuit
D.faulty suction pressure regulator
单项选择题 The purpose of the wearing rings used in a centrifugal pump is to （）.
单项选择题 The lowest temperature required to cause self-sustained combustion of a substance independent of any outside source of ignition is called （）.
单项选择题 If a refrigeration compressor will not start, the reason may be （）.