Answer:
Wash oven racks in the sink with warm water and the ammonia/detergent solution. Sometimes oven racks can be particularly hard to clean. If they’re still stubbornly soiled even after the overnight-ammonia treatment, try putting them inside a large, dark garbage bag. Pour a half-cup of ammonia over the racks inside the bag, tie the neck of the bag and place the bag outside for a few hours. Bring the racks inside, wash in the sink and wipe clean.