A Japanese research group focused on odor production mechanism and odorants. They found that the odors caused by ACS evaporators mainly occur when the surface of evaporator becomes wet and dry (A/C off →on and A/C on →off). Furthermore, these odors stimulate drivers’ nose, and consequently make the drive unpleasant [3]. On the other hand, American research groups have focused on microorganisms to resolve ACS odor problems. Simmons et al. found that insulation materials which absorb moisture and volatile organics appear to provide suitable substrates for fungal colonization [5]. Simmons et al. also found that climatic conditions (high humidity) and airborne fungal populations are undoubtedly major factors in the incidence and severity of fungal colonization. Automobiles once colonized by fungi may continually or sporadically emit noxious odors or sensitize products that affect the occupants of the automobile. In most cases, automobile engines and ventilation fans are seldom kept running after the air-conditioning system. Running the engines and ventilation fans for a short time would reduce the moisture residues that are necessary for the growth of the fungi [5]. A study on mixed biofilms in automobile air-conditioning systems shows that bacteria and fungi may form mixed, desiccation-resistant biofilms on the metal heat exchanger fins within the core of ACS evaporators as well as on forms, plastics, and other components. These mixed biofilms when moistened may be major contributors to episodic noxious odors in automobile air-conditioning systems [6]. Moisture retention, even episodic events, within the ACS in conjunction with such biofilms appeared sufficient for odor production. The accumulation of bulk organic debris, leaves, insects, etc., of course could help in initiating the microbial problem, but most units with odors that were examined were free of such materials. Methods to reduce or eliminate the moisture retention in the ACS, coupled with less susceptible orอ antimicrobial substrata, would seem the most practical means for controlling microbialassociated VOCs [7].