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2010 Toyota Prius mildew smell after using AC

Hi! Thank you for the show :slight_smile:

I know you only get questions about vintage and real cars. This one is about hybrid (does not relates to the fuel though).

There is one thing both dealer and me can’t sort out.

When after winter it starts getting warmer, turning on AC produces this weird smell, like a mildew.

Tried to use the anti-mildew aerosols and foams but it helps few days, week max.

Any advice to manage that smell in warm months?

Thank you again!

Alex from Arlington, VA.

Did they check the AC drain?

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Call local detail shops, and ask if they have ozone generating/ionizing equipment.


Thank you, everyone!
They did check the drain and it is clean and open.
As for the ozon, smell is only on when AC is on. Turn off AC and open window - all is good.
My understanding is that ozon removes smells like tobacco that are always present.

Not that it is important but the show has been reruns for several years and very few stations are airing them now.



You have mold/mildew where the aerosols can’t reach.

Conditions just have to be right for the stink to occur.


Oh I see.
I will try this one!

And the applicability of your comment to this forum is what? The idea of this website is to provide information and help for those who request it.

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That is providing information. There are a ton of people who’ve heard of Car Talk, but that may not know that the show is no longer active anymore. My grandmother only figured it out when our local NPR station stopped running the Best of Car Talk series on Saturday mornings.

It appears the OP may think the show is still in production so letting him know it is not is providing information.


Have you replaced the cabin air filter recently? It’s really easy to do and you can use a generic part from your local auto store.

Yes, air filter is being replaced when needed.
I’ve also did replace the filter when applying this anti mildew foam.

Still smell appeared after some time again.

Is that smell a common thing or no?


Get it checked by another shop. Maybe this dealership mechanic didn’t check the drain hose and the service writer miscommunicated, maybe they lied to you, or maybe they weren’t thorough enough to find the clog.

Based on your symptoms, I’m pretty sure the drain hose for the air conditioner is bent or clogged, and water is flowing from the evaporator coil into the carpet on the floor. There isn’t much else it could be unless the timing of this is completely coincidental and you have a sunroof leak or some other type of leak where there is water intrusion.

If you don’t want to take the car for a second opinion, drive around with the air conditioning on and then park it in your driveway. If you don’t find a puddle of water underneath after a few minutes, that hose is still clogged or it has a kink in it.

One cause of this smell is operating your A/C in the recirculate mode too much. That builds up moisture that promotes mold. Use outside air most of the time.

The only other advice I can offer is that you run the fan in the fresh air mode regularly at least a few miles every day. My wife has a 2006 Prius and this smell is common because the recirculation mode is the default on this car. One of our mechanics recommended this and it definitely helps. Climate is also a factor. We live in Nevada where it’s mostly dry. More humidity=more likely mildew will grow. Hope this helps!

Thank you, everyone.
All advices make sense.

Will keep you updated. For now it’s snowing so I’m waiting for a smell to come back first

I’m not sure I agree with that assessment or the theory behind it. Whether you use the A/C in recirculate mode or you bring in outside air, the moisture should flow from the evaporator coil through the drain. The airflow should make no difference.

I’ve seen warnings in vehicle owner’s manuals that warn against using the heat in recirculate mode because it will lead to a buildup of humidity inside the car, but knowing what I do about the basic operation of air conditioning, I don’t see why using the A/C in recirculate mode will lead to more moisture inside the car. If everything is working like it should, recirculating the same air should often actually lead to less moisture in the drain, especially if it is humid outside.

Is there something I’m missing?

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I found a mouse nest on top of the cabin air filter in my 2013 Chevrolet Equinox after the car started to smell like something died in the dash.

I ended up spraying about 1/2 can of Lysol into the hood cowling with the heater fan on max while rotating through the defrost, vent, and heater air flow selections to distribute the Lysol through the system. That was 3 years ago and I haven’t had any recurrences since.

Ed B.

We park in our attached garage…kind of a necessity I think, in snow-belt Maine, and we always open all the windows. Lots of moisture (snow, slush) gets into vehicle via our feet when we are out and about. So any airing just helps. We keep the garage windows shut in the winter…but it is in an uninsulated section of building so there is still a good air flow under garage doors, etc.

Hope that helps?