Fungi are usually spread in humid areas, even if they are scarce in nutrients, which can capture a small amount of them from the surrounding air.  Fungi in air-conditioner windows were studied in 13 air conditioners in houses located in Sakaka city, Jouf, Saudi Arabia, in the spring of 2018. Air passages inside these air conditioners are suitable environments for the occurrence of fungi.  This research was designed to reveal the presence of dangerous fungi in air passages of these conditioners and to find suitable practical ways to eliminate these harmful taxa. Isolated fungi were identified using morphological and ultrastructure criteria and were Aspergillus niger, Chaetomium  globosum, Penicillium  frequentans, Penicillium italicum, Paecilomyces lilacinus, and Xanthophyllomyces dendrorhous. Results showed that Aspergillus niger, Paecilomyces lilacinus, and Penicillium italicum caused severe decomposition of in human blood red cells, the strongest of which was the fungus Paecilomyces.  The aromatic pungent smell of transcendental naphthalene has been shown to have an inhibitory effect on three of the isolated fungal species. Transcendental naphthalene inhibited mycelium growth of Aspergillus niger,  Penicillium frequentans and Penicillium italicum by 100% while never affecting Paecilomyces lilacinus.  The study recommends further studies on the presence of fungi in the air - driven corridors of air conditioners in different countries and devising new ways to reduce the presence of fungi.