I have a high efficiency 5000 central air conditioning unit that is not cooling, it is running but the air is not cool. It is model CA5536UKA1 serial LP31232822
Date of unit 3/1993. Could someone tell me what to look for or if it is low on freon.

If the compressor inside the unit is not running then the problem is with the compressor or associated parts. If the compressor is running the valves in the compressor could be bad or you could be short of refrigerant or a host of other problems.

Best to get someone to come out and check it out with a set of guages, that will tell the story,, if they know what they are doing.