The model number I copied off the back of our 11 1/2 year old Bryant Furnace and Air conditioner unit in basement is CK5BXA042021AAAA. Our house was a new-build by Centex and the new owner's book that came with the house indicated that we should have received an owner's manual for that system.....but that never happened. Have been trying without any luck on the internet. Happily, we have had no trouble with the system but would like to have a manual just in case.