While air fresheners can help to mask unpleasant smells, it is not recommended to put them in AC units. The chemicals in air fresheners can interact with the AC unit's filters and other components, reducing their efficacy and potentially causing damage. In addition, the fragrance from air fresheners can become trapped in the AC unit, causing it to circulate throughout your home. This can be especially problematic for people who are sensitive to strong smells or who have allergies.