If your car air conditioner smells like ammonia, there could be a few different reasons why. Ammonia is a chemical that is used in some air conditioning units as a refrigerant. If there is a leak in your air conditioning unit, the ammonia can escape and cause an unpleasant smell. Another reason why your car air conditioner may smell like ammonia could be because of bacteria growth in the unit. Bacteria can grow in moist, humid environments, and if not cleaned properly, can cause an ammonia-like smell. To clean your air conditioner and remove any bacteria growth, you can use a vinegar solution or speciality cleaners made for cleaning air conditioners.