Today my a/c unit is not blowing much cold air. Both the outside fan and the inside fan are working. I even checked the belt. I can hear it run but it never completely kicks in? Any suggestions?

My a/c unit is not blowing much cold air. Both the outside fan and the inside motor is working. I can hear it run it just never completely kicks on. Any suggestions?

More info needed,, what name brand and model number,sounds like its pretty old if it has a belt,if it does check to see if its loose and slipping