单项选择题 Sludge may form in the lubricating oil crankcase of a reciprocating air conditioning compressor as a result of （）.

单项选择题 In a chilled water air conditioning unit using a reciprocating compressor, the refrigerating effect of the primary refrigerant can be increased by （）.

单项选择题 A re-heater in an air conditioning system functions to （）.