My air condition has been working very well.I've been running it now on 79 degrees for the past week,due to this 90 degree weather.I come home from work today to realize that there's no air coming out of my vents,but the fan is blowing outside.. Please can you tell me what's going on with my unit

Sounds like the relay switch went bad. My a/c in Florida used to do this all the time. You can try turning it completely off as it may have frosted up, but that is only in rare occasions. Don't mess with your a/c unless you know what you are doing as you can get a heck of a whallop from the unit and maybe fry yourself. Have someone who knows what they are doing check out the individual components with a multitester to see which switch went bad.