Pour the apple cider vinegar, onions, carrots and celery over the top of the hot macaroni noodles and toss until combined. Let the mixture sit in the fridge for 15 minutes, or until cooled.
While cooling, start on the dressing. In a large mixing bowl, add the mayonnaise, half and half, brown sugar, salt and pepper. Stir until well combined, and add more salt, pepper to taste if needed.