Bring a large pot of water to a boil and add chicken bouillon. Cook macaroni until soft.
Whisk together mayonnaise, milk, apple cider vinegar, and sugar in a large mixing bowl. Season with salt and pepper to taste.
Once macaroni has cooled, place it in a clean mixing bowl along with the carrots and onion. Pour dressing over macaroni and mix well, coating all of the pasta. The salad will look a little loose, which is normal – it will absorb in the refrigerator.
Cover and refrigerate for at least 1 hour to allow the flavors to meld. Before serving, mix well and top with green onion.