Sometimes your air duct system is just too damaged or worn out to be cleaned. This might occur because of damage by animals, flood, fire, or rust.
In other, less extreme case, The Clean Air Co. LLC. may be able to clean the ducts after performing some minor repairs, depending on how damaged or worn out your duct work is. Occasionally we find duct work that has just aged and is coming apart due to the heat and cold in the crawl space. This is a repair that we can usually make. Then we can clean the air ducts as we normally do.