Ammonia is a very irritating substance and should not be used to evict a chimney-dwelling raccoon. Chances are the raccoon is a female raising young on the smokeshelf. If you use ammonia, the young, which are too small to climb out, will suffer needlessly. Furthermore, the use of such chemicals for the deterrence of animals may be prohibited or restricted in your particular state (an illegal pesticidal use). Please consult your state wildlife department for requirements.

If you are in a hurry to have the family removed, hire a qualified professional. Visit Service Vendors for links to information on how to hire a qualified professional.

If you are not in a hurry, play a loud radio during daylight hours for several days. The noise, although there is no guarantee, might sufficiently disturb the female to cause her to move her young to another "safe" site (from the mother's perspective). When she and her young are gone, have the chimney flue capped with a professionally manufactured screen, preferably stainless steel.

Look for the location around your house where the raccoon is accessing the roof. Once the offending animal has left, take permanent steps to limit access to your roof. This may involve installation of flashing around the bases of adjacent trees to prevent raccoons from climbing, pruning of overhanging branches, or, as a last resort, removal of adjacent trees that provide access to your roof. Finally, be sure to locate and safely remove any raccoon toilets; see FAQ #863 on raccoon roundworm.

For more information, visit
Raccoons
http://www.hsus.org/web-files/PDF/raccoon-fact-sheet.pdf