Curing Springtime Air Conditioning Smells

Air conditioning odors typically result from the uncontrolled growth of bacteria and other microorganisms in the evaporator. Research by independent laboratories has found fungi such as Aspergillus, Cladosporium, Penicillium and others growing on cooling coils and other A/C system areas.

How do these microorganisms get there? They are naturally present in outdoor air and are drawn into the evaporator during air conditioner operation. Moisture also contributes to A/C odor formation. Most of the moisture 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 and mildew to grow and generate musty odors.

To get rid of the unwanted organisms, various chemicals can be sprayed on the evaporator directly or through the blower ducts or air intake. Some of these chemicals are designed to be applied by DIYers. However, independent repair shops and dealerships that provide A/C service can offer some of these de-smelling solutions.

A musty odor may be emitted from the air conditioning system of some vehicles that are usually operated in areas with high temperatures and humidity. It's most noticeable when the air conditioner is first turned on after the vehicle has been parked for several hours.

The odor could result from one or more of the following conditions:

As carmakers downsized vehicles while also increasing their glass content in recent years, A/C system manufacturers reduced evaporator size while simultaneously increasing fin count. Thus, these densely packed evaporators trap and hold more moisture.

To see this for yourself, dip your hand into a glass of water. As you remove your hand from the water, quickly spread your fingers apart. No water will bridge the gap between your fingers. Dip and remove your fingers again, this time spreading them slowly to only a fraction of an inch apart. Water will bridge the smaller gap between your fingers and remain far longer than if you open your fingers wide.

Some odor treatments are merely feeble attempts to cover up odor. Here is a brief description of the performance capabilities of various odor treatments by product type: