单项选择题 If a bilge pump is able to develop vacuum, but is unable to sufficiently pump out the bilges, you would check for all of the following EXCEPT （）.

单项选择题 The principal purpose of sub-cooling liquid refrigerant prior to its entering the expansion valve is to （）.

单项选择题 Refrigerant is normally sub-cooled in a refrigeration or air conditioning system condenser to （）.