单项选择题
A.system is low on refrigerant
B.high pressure cutout switch is improperly adjusted
C.discharge valves are leaking slightly
D.discharge valves are leaking excessively
单项选择题 Excessively low air pressure occurring in the intercooler of a reciprocating air compressor is caused by（）.
单项选择题 Most pump manufacturers recommended that the discharge piping for centrifugal pumps be （）.
单项选择题 If a refrigeration compressor is short cycling on high head pressure, you should （）.