I answered a couple of questions concerning window air conditioners, as it is nearing the end of the season:
Here are the answers to a few of the inquiries: If you (or your tenant) noticed a moldy odor when the unit was running, clean out the drain hole. That is the usual cause of mold, since the water is puddled and stagnant. Clean the fan and the evaporation coil before covering it for the winter; it will be easier than when the crud has been there all winter. Clean or change the filters so they will be ready to go in the spring.