A Florida-based law firm calls it “sick car syndrome”. Major automakers have bought back or refunded the purchase of cars and light trucks because of it. It affects an unknown number of drivers and passengers and compared to the similar “sick building syndrome” it’s almost completely unresearched by the medical community. Symptoms can be anything from nasal irritation to allergic reactions; a growing phenomenon with a major source that’s literally under motorists’ noses: air conditioning evaporators and associated air ducting. The normal cause of consumer complaints are mold growth, generally inside the evaporator case. Why there? It’s mainly about the relationship between dew point and temperature. The dew point temperature is defined as the temperature of the air when the relative humidity is 100 percent. Relative humidity is defined as the amount of moisture in the air relative to the most moisture the air can hold at the same temperature. As air is cooled it loses its ability to hold moisture. So, relative humidity is increased by cooling the air, as well as by adding moisture to it. For example, as the air cools on a muggy night the relative humidity increases. When the relative humidity reaches 100%, the air has been cooled to its dew point and liquid water forms on surfaces. In automotive A/C, once the air is cooled below the dew point, the air releases moisture which is deposited in the evaporator case and is drained outside. Ideally, cooled and dried air is delivered to the passenger compartment, air dry enough that modern defrost cycles use the A/C system even in cool weather to clear windshields faster. It’s a law of physics that humid air will leave condensation when cooled and anything that’s sufficiently wet and warm will encourage mold growth.
According to American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), if relative humidity exceeds 70%, mold growth may occur due to wetting of most materials. For building materials the society recommends that porous materials be dried with fans and heating within 24 to 48 hours of becoming wet. If porous materials are not dried within this time frame, mold growth may occur.
What can you do about it? There are two service strategies that should be employed together if mold growth is suspected in the passenger compartment. The first is mechanical. Air conditioning is always suspect, but feel the carpets and peel back floor mats to check for dampness on both sides of the car. Bad seals around doors and windows can leak rainwater into the floor pan, creating a moist, mildew-prone environment. Check to ensure that the evaporator case drain tube is clear and is freely draining the case. Foreign matter like leaves and pine needles in the cowl fresh air intake can also trap moisture, so a thorough cleaning of that area is warranted. The evaporator case itself is generally too difficult to split for this kind of service, so choices at this most likely trouble spot are more limited. Aerosol sprays are the primary weapon against mold here, usually by spraying through any available access points like seals or blend air doors. By their design, however, evaporator cases are airtight so some disassembly is almost inevitable. Access is another issue, which may be as simple as reaching under the dash to routes through the glove compartment. Unless the symptoms are severe, it’s unlikely that the average owner will authorize an expensive assault on the dashboard, but there are a couple of back door approaches that can help. One is to drill a small access hole in the evap case and spray the fumigant into the opening. Reseal the hole when you’re done and the system is good as new. The primary caution when using this method is the need to operate a whirling drill bit in a dark awkward place next to an expensive heat exchanger that’s pressurized with R-134a. A slip here is potentially very expensive. To minimize the chance of damage, select drill motors and bits that reduce the risk. Cordless units with variable speed are a good choice, keeping in mind that a clean hole in plastic requires enough breakthrough bit speed to keep the bit from “threading” the hole and drawing the bit rapidly into the evaporator. Step drills are a good choice, as are drill stops set to minimize the penetration depth into the plastic. It’s also possible to use a short or broken drill for the same reason. Bits should be extremely sharp. If a dull bit requires significant force to penetrate the plastic it may plunge into metal when it breaks through.
Once the case is holed, it’s a simple process to spray the interior. The important point here is to remember that close enough isn’t good enough for this type of service. If you fail to get it all, mold can grow back quickly, so be generous with the aerosol. If you’re in doubt about coverage, use another can, and remember the ducting and dash vents. General deodorization can be handled by spot products or by area sprays that are pulled through ducting and evaporator by a system running on “recirculate”. Don’t forget to reseal the hole in the evaporator case. Replacement of the cabin air filter is a natural service at this point, too. By now, the interior of the vehicle should smell sweet; a quick interior vacuum and an ashtray check also helps emphasize the value of the service.
And value is the key to making this form of A/C service work. Some owners will complain of a slightly musty smell, while others experience real distress. Highly allergic consumers may have multiple triggers and will likely be highly sensitized, so it’s important to do a thorough job and let them know what you did, preferably on the work order. This point is especially important if you’ve spent considerable time on the vehicle, probably getting access to the evaporator case. Remind the owner that non-use of the system is a contributory factor; chances are they avoid using the A/C system because of their sensitivity, making the system more prone to mold growth. And remember that the car is only one source of potential exposure. A “sick home” or “sick office” is a problem you can’t service in the bays, but may be major factors in an owner’s experience. You can’t do a thing about that, but you can take the family car or truck out of the equation. It’s a rarely considered and almost never advertised form of automotive service that might have lots of takers in your market.
Can automotive A/C really be a factor?
According to Dr. Bradley Marple, associate professor of otolaryngology at the University of Texas Southwestern Medical Center at Dallas, the answer is yes. In a study published in the Journal of Respiratory Diseases, May, 2001 another Canadian study is quoted that involved 403 children, reporting that the incidence of respiratory symptoms increased by as much as 50 percent in homes with measurable fungal growth. While the exact mechanism that causes the irritation isn’t fully understood, the study reveals that the emission of “secondary metabolites” by fungi may cause respiratory inflammation without an allergic reaction. Fortunately, they also release “microbial volatile organic compounds” which give the telltale musty odour that warns of the growth. While the study notes that household duct cleaning does reduce growth in home air conditioning systems, it also acknowledges that there is very little research on the subject related to mobile A/C. The study does note, however, that keeping the air flowing is still important: “The dynamic use of the ventilation system appears to be associated with less favorable conditions for fungal growth by way of decreased available moisture within the system.”
Formal scholarship on the subject is thin on the ground, but the subject has been studied at least as early as 1997. In an article reported on general interest website healthcentral.com, for example, Dr. Robert Simmons, manager of the Biological Imaging Facility at Georgia State University stated that “there are fungi in the air-handling system of cars … similar to fungi that we find in the ‘sick building syndrome’ situation”. In the GSU testing, 27 car A/C systems were “swabbed” and all revealed the presence of fungi, (two types of fungi called Cladosporium and Penicillium) although not everyone is sensitive to the growth. If regular household duct cleaning is a good idea, why not the same for the family car?