单项选择题
A.excessive condenser cooling water
B.warm food in the refrigerator
C.a shortage of refrigerant
D.s shortage of compressor oil
单项选择题 Thermostatic expansion valve are （）.
单项选择题 When a hydraulic vane pump is working, which of the following is in contact with the vanes?（） (1) the rotor (2) the internal surface of the housing (3) the external surface of the housing
单项选择题 Which of the following items is necessary for all waste heat boiler installations, regardless of design or manufacturer? （）