Causes and Cures of A/C Odor

Air conditioner odor complaints are a common consumer problem. Why? A/C system odors typically result from uncontrolled growth of bacteria and other microorganisms in the evaporator part. Nasty little beasts like aspergillus, cladesporium and penicillium grow on cooling coils and other areas. How do these beasts get there? They are naturally present in outdoor air and are drawn into the system through the evaporator during system operation. Moisture also contributes to A/C odor formation. Most of it that condenses on cold surfaces inside the system drains harmlessly over time. However, some moisture continues to cling to coil surfaces after the A/C shuts down. Microbial contaminants in the air combine with this lingering moisture in the evaporator. The warm, dark and moist conditions in the evaporator provide an ideal breeding ground for bacteria, mold, mildew and nasty beasts to grow and generate musty odors...think about old sneakers left in a locker over the summer! Stinky! Cures for A/C Odor Some odor treatments are merely feeble attempts to cover up odor. They are doomed to fail. Almost all odor treatment products fail to provide a long-term residual effect that can reduce the reoccurrence of odor. Here is a brief description of the performance capabilities of various odor treatments by product type. Perfumes/Fragrances: Are designed to cover up odor with another, more acceptable scent. Can be time-release agents. Cover-up perfumes and fragrances cannot eliminate odor-causing microorganisms. Disinfectants: Destroy odor-causing microorganisms on contact. The typical liquid disinfectant quickly evaporates or washes out of the system along with the condensation that forms during air conditioning use. The next time airborne bacteria enters the system, odor can begin again. For this reason, disinfectants can require frequent repeat application to control odor. Smoke/Mist Application: Smoke and mist products combine a liquid disinfectant with a fogging application technology. The fog is directed toward air intake vents inside the passenger compartment, drawn through the air conditioning system and then spread throughout the vehicle. The fog’s fine mist allows ease of application, but may not provide a liquid’s saturation effect that is required to eliminate the kind of microbial infestation that typically causes air conditioning odor comebacks. The fog quickly dissipates from the system, leaving no long term protection against odor recurrence. Air Filters: Catch and absorb particulates and some gases as they pass through ducts to the passenger compartment. Many filters use activated charcoal. Even with active ingredients, some filters cannot catch the molecules that cause odor, because they are (microscopically) tiny microorganisms. If these microorganisms are small enough to pass through, the filter cannot prevent the resulting odor. Finally, filters become saturated or their active ingredient loses effectiveness over time, and must be replaced. Baking Soda/Absorbents: Absorption of moisture reduces the ability of microorganisms to multiply and cause odor. Absorbents become saturated quickly and allow odor to return, thus requiring repeat application. Chemical Reactants: Reduce odor by combining chemically with molecules of the odor-causing microorganism. The new, combined molecules must then be removed (wiped up with a dry towel, washed away in a liquid, etc.) to complete the odor treatment. Like liquid disinfectants, chemical reactants wash out of the system quickly with condensation. They can allow odors to return quickly. Antimicrobial plus Coil Coating: One unique antimicrobial product used on mobile air conditioner odor combines its active ingredient with an acrylic resin that is sprayed into the evaporator. The acrylic resin dries onto the evaporator coils, forming a coating that sheds moisture better than uncoated coil surfaces. The antimicrobial agent remains embedded in the coating, where it inhibits the growth of any microorganisms that attempt to settle on the coated surface. Together, the antimicrobial and acrylic resin coating last in the A/C system for up to three years, protecting against moisture buildup and the growth of odor-causing microorganisms on coated surfaces. When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere. You can E-mail us at [email protected] or visit to find a Mobile Air Conditioning Society repair shop in your area. Visit to find out more about your car’s mobile A/C and engine cooling system. Thanks to MACS member Airsept inc. for this blog contribution on understanding A/C system odor.

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