a/c stopped blowing cold and service eng light came on to

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left work and a/c stopped blowing cold,then started blowing cold @ 40minutes later;next morning, on start up,car would make noise for about 20 seconds but a/c would blow cold air..then 3 days later, a/c stopped blwing cold air and the service eng light came on..car drives fine..tech at auto parts store, said no codes were showing..what can be the problem ?