Place the frozen potatoes in a dutch oven and cover with water. Heat enough to break potatoes apart, turn off heat and let set a few minutes. Drain well and place in 6-quart roaster or crock pot.
Cut the bacon into 1-inch pieces. Warm in a small skillet to release flavor and crisp. Keep warm.
Combine the flour, sugar, salt and celery seed and set aside.
Combine the water and vinegar and set aside.
Melt lard in a deep 10-inch skillet (chicken fryer). Sauté the celery until it begins to turn golden. Add the onions and continue until the onions are translucent. Add the warmed bacon and any drippings that collected. Combine all well.
Sprinkle the flour mixture over the vegetables and bacon and combine well.
Add the water and vinegar a little at a time, stirring constantly, until all has been added. Bring the dressing to a boil, stirring constantly, then reduce heat and simmer for 2 minutes.
Pour hot dressing over potatoes and combine well. Cover container tightly with foil and refrigerate, overnight if possible. Before serving, heat to serving temperature 3-6 hours depending upon appliance used, stirring about once an hour.