The ads emphasize how easy the Klima-cleaner is to use, in that you only have to stick the hose in the dash a/c vents and spray. The actual instructions appear to say that you should access the evaporator and spray it into the evaporator; if you are not able to do that then the dash vent thing is less effective but consumer friendly:
QUOTE
Klima Cleaner comes with a 2 foot tube with a brass tip on the end that foams the product upon exiting the tube. The goal is to get the product in the box which is located deep inside the dash. Several ways of getting there: 1) inserting the tube into the center vents, 2) after removing the filter, insert the tube as far deep as possible, 3) the evacuation tube (mentioned above) where condensation is allowed to exit or 4) the inspection pit. The last two areas are the most effective. The first two are not as effective but the most consumer friendly.
If you don't have any odor from the A/C this is a product I would skip. If you do have odor from the A/C first try replacing your cabin filter if your Cadillac has one. Next consider cleaning the evaporator. Last, a product such as Klima-cleaner may work well for you.