Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until cooked through but firm to the bite, about 8 minutes.
Drain.
Whisk mayonnaise, milk, and sugar together in a bowl until smooth and creamy.
Stir elbow macaroni, crabmeat, Cheddar cheese, and peas together in a large bowl.
Pour mayonnaise mixture over crab mixture and stir to coat. Chill in the refrigerator for at least 3 hours.
