In large saucepan, cover potato slices with water. Cover and bring to a boil; reduce heat. Cook 10 to 15 minutes or just until tender; drain.
Transfer potatoes to large serving bowl; set aside.
In small saucepan, cook onion in 1/4 cup of the apple juice until tender; remove from heat and set aside. Do not drain.
Place flour in small bowl. Gradually add remaining 3/4 cup apple juice, stirring until blended and smooth.
Stir flour mixture into cooked onion mixture in saucepan. Add celery seed, salt and pepper. Cook over medium heat, stirring constantly, until mixture comes to a boil. Boil and stir one minute.
Remove from heat. Add vinegar. Pour over potatoes in serving bowl. Add bacon. Toss gently to coat. Sprinkle with parsley. Serve warm.