单项选择题
Before charging a refrigeration unit, the refrigerant charging lines should be（）
A.flushed with clean refrigerant oil B.purged with the refrigerant C.washed with an ammonia and alcohol solution D.grounded to compressor
单项选择题 In the presence of an open flame or hot surfaces, chlorinated fluorocarbon refrigerants decomposes and from （）.
单项选择题 In an operating refrigeration system low on refrigerant, a liquid line sight glass will（）
单项选择题 The thermal expansion valve reacts directly to the （）
