Prepare gelatin by combining boxes with 2 cups boiling water. Stir until completely dissolved. Add 1 cup cold water. Chill until thickened.
While gelatin is chilling, mix the pineapple, cranberry sauce, and mandarin oranges in separate bowl. Mix to break up cranberry sauce gel.
When gelatin is thickened but not set, with rotary beater, combine container Cool Whip with gelatin till mixed well. When mixed, add fruit mixture and pour into 5 cup mold. Chill until firm and set. Remove from mold for serving.