单项选择题
A.re-adjust the discharge pressure
B.clean the expansion valve screen
C.add refrigerant
D.adjust the expansion valve
单项选择题 On small, low pressure, air compressors, the cylinders are usually lubricated by the （）.
单项选择题 While troubleshooting a refrigeration system for low head pressure, liquid refrigerant flooding back from the evaporator is determined to be the causeIt may be necessary to （）.
单项选择题 Air trapped in the hydraulic fluid of a steering system should be indicated by （）.