Ask The Beaverton Car Guy: What’s that Smell Coming from the Vents?

By Larry “The Car Guy“ Ferguson


Hello Beaverton Readers!

In January near the first of the month, I received a call from Edward from Beaverton. Edward mentioned that he had noticed a musty smell in his newer GM SUV during the summer months while using his A/C and now that the weather has changed, the smell has become worse and stale. Does switching the air ventalation mode make a difference?

Prevent window fogging by using fresh air with AC

All vehicles equipped with air conditioning will run the A/C when the defroster is in use. This is part of the dehumidifying aspect of the A/C which will basically aid in the de-fogging of the windows as well as drying the cabin air during colder months. One of the important things to make sure of is that the switch is set to fresh air during the winter months. If it is on recirculate, it keeps stale, wet air inside the cabin which will cause your windows to fog.

Have you ever noticed how foggy your windows get when you get into your car with wet clothes and jacket? It is very simple to reduce this fogging with a couple of simple vehicle operation settings.

Step#1 is set the vehicles heater-AC control panel to the fresh air setting (it will have a picture of a straight arrow coming into the front of the vehicle from outside).

Step #2 press the Air Conditioning button, with the heater temperature on hot. This will not only allow the stale wet air to escape, but will also cause the Air Conditioning to dehumidify the passenger cabin, and clear the windows more quickly. Don’t worry about cooling the cabin because the air will pass by the heater core first heating the air.

When use the recirculation mode?

The recirculate setting on the heater control is to be used during the summer months. If it is set to recirculate, it will re-cool the already cooled air without allowing the hot outside summer air into the passenger cabin.

Musty Smells

Here is some helpful information to keep this musty smell to a minimum. Trying to identify car smells can sometimes be baffling, but one thing is for sure, there is an answer.

One of the most common smells people complain about in vehicles is a musty or stale smell. The best air fresheners will not remove the smell because the source is still there. The most common cause of this car odor is the air conditioner which removes moisture from the cabin and drains it at the bottom of the evaporator.

The best way to prevent car smell is to dry the evaporator before shutting off your car. If you run the blower motor/fan without the air conditioner on for about 2 minutes before shutting off your car, it will dry the evaporator fins and most of the moisture will evaporate, leaving nothing to cause that odor.

Thank You

I hope this information is helpful to all of our wonderful Beaverton readers. Once again thank you to all of you who have written in or called me to ask questions, I enjoy helping very much. I would also very much like to thank all of you who have used my brokering services when needing to purchase a new or pre-owned vehicle. Not forgetting those of you who have asked for help in selling your current vehicles, or extra vehicles that are no longer in use.

Larry’s specialty is locating cars, even hard to find cars, for everyday folk. He has been in the automotive industry for over 35 years and has several degrees in automotive technology. Email him at or call 503-930-1493