My a/c ceiling unit is set at 78 degrees but it stopped blowing cold air,I did turn it off for 2 hours and turned back on and started blowing cold air for just over 24 hours. But is now just blowing warm air.

Th evaporator is probably icing up and restricting air flow.THis could be caused by a dirty air filter,dirty coils or low on refrigerant. Check your air filter clean the coils on outside unit. You will need to call in an experienced tech to clean the inside coils and to check the refrigerant. Good Luck