I have worked for 25 years or more in Auto industry and have come across many customer complaints of “sour milk” like smell from their vehicle’s air-conditioning unit. No one knew the real reason and we resorted to many methods to overcome them. From interior cleaning, steam treatment, cleaning/replacing the evaporator coil/filters, adding perfume and others stuffs to suppress the smell. We even tried leaving chunks of charcoal under the seat.
I have since left the industry and have used many cars – never had this experience until recently. My new car after about 3 month of use is showing symptoms of this smell. My previous cars did not have it. What I stumbled upon was entirely unexpected. I found out that the “prime suspect” of this smell to be the tinting done on the car, although I do not have sufficient facts to “charge”. And it is not with any kind of tinting, it is specially from tinting that has an incorrect or unbalanced of UV filtration against permissible solar energy into the cabin that does not help in killing some germs.
Resulting from our perspiration and skin dust that discharged in the cabin, it makes way into the air conditioner. The evaporator coil is wet all the time, even long after we have switched off the car creating a perfect environment for the microbes to live and even mutate. It seems to correlate with the percentage of UV filtration vs. solar energy that inhibits the elimination of these microbes.
The main forms of ultraviolet light that reaches us from the sun are called ultraviolet A (UVA) and ultraviolet B (UVB). These are the same wavelengths of light that are used for medical therapies. Ultraviolet light causes changes in cell DNA leading to cell damage and possible cell mutations that can turn a normal skin cell into a cancerous one. As we know, UVB rays are those responsible for sunburn. UVA rays penetrate skin more deeply, and it's increasingly recognized that they also set the stage for skin cancer development. UVA is the predominant type of ultraviolet light that comes from tanning beds.
In the same manner and effect, we need to let some UV enter our car when we are not in it. It helps eliminate the microbes that we leave behind before it gets into evaporator coil. I have branded cars with 7 stage cabin air filters, plasma clusters and carbon filters. But some of these cars suffer the same issue.
To be certain of this theory, I am going to remove the RM2k tinting on my car and observe, if there are changes. Pending which, I seek cooperation from all the Tinting producers not to file a law suit.
What a discovery after being in the automotive industries for so many years, the clue came just after I retire.