Never use products with ammonia to remove cat urine odors by: Anonymous
Finding the exact spot is important, so finding the offending area will show up using a black light if you can get a hold of one. This way you can find the offending exact location and get rid of it.
Some uses I found was:
15 ounces of hydrogen peroxide, two tablespoons of baking soda, and two squirts of liquid hand soap. Mix in a plastic container with a plastic spoon. Discard after use.
Apply this solution to cat urine stains or odor areas, and then rinse away with warm water.
Try Simple Solution or Natures Miracle You may need to remove the air duct and clean inside, as well as soak the cover.
OdoBan
Just remember after using any natural or store bought product. clean the area again with the proper cleaner for the type of flooring, carpeting etc to prevent damage from these products. Good luck.