Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

i'm looking to remove an odor from my Corolla's fresh air intake.

There are products available where you spray the product into the fresh air intake (near the windshield wipers), while the fan is running full speed:

enter image description here

Toyota has a blurb about how to perform something similar yourself:

What causes air conditioner odor? How can I prevent the odor from occurring?

... spraying a mixture of isopropyl alcohol and water (1 to 5 ratio/mixture) or a disinfectant in the outside air intake may help reduce the smell.

Now the idea of spraying an aerosol into my car's electric fan makes me kind of nervous:

  • the product in the spray can is (almost certainly) flammable and explosive - yet Toyota itself uses the same thing
  • i've also seen videos of people spraying Lysol into their fresh air intake to remove odors. A can of Lysol can double as a flame-thrower for those with too much time on their hands
  • i also bought a can of AC deodorizer that contains iso-butanol; and has flammable warnings on the can
  • and finally we have Toyota recommending spraying isopropyl alcohol (i.e. rubbing alcohol) into your intake

i'm willing to try the isopropyl alcohol, but i'm confused about the ratio. They recommend 5:1 ratio. Is that:

  • 5 parts alcohol, 1 part: 83% alcohol, or
  • 5 parts water, 1 part alcohol: 16% alcohol

Again, their wording:

a mixture of isopropyl alcohol and water (1 to 5 ratio/mixture)

i came across a forum post where a person said something to the effect of:

i already know about using isopropyl alcohol (5 parts alcohol with 1 part water)

Which is the opposite of how i read Toyota's instructions.

i did some tests:

  • 91% isopropyl alcohol: flammable (9:1)
  • 70% isopropyl alcohol: flammable (7:1)
  • 50% isopropyl alcohol: not flammable (1:1)
  • 13% isopropyl alcohol: not flammable (1:5)

13% isopropyl alcohol is very watery - with a lot of water left over (it doesn't evaporate very well).

So my question:

How much isopropyl alchcol to deodorize AC ducts?

Or am i being too cautious?

share|improve this question
up vote 3 down vote accepted

a mixture of isopropyl alcohol and water (1 to 5 ratio/mixture)

means 1 measure of alcohol to 5 of water. You wouldn't want to go the other way, in my opinion as you'll end up with a lot of alcohol, which will not only be a fire risk, but also could do bad things to duct work etc.

share|improve this answer

i ended up using, after extensive testing, a 50-50 mixture.

Turn fan on full-blast, and use spray-bottle to spray mist into the intake.

Odor eliminated; i was surprised it worked.

share|improve this answer
What volume of the 50/50 mixture would you say you ended up using ? Did you remove the A/C filer while doing so ? – Bertrand Caron Jan 27 at 22:07
@BertrandCaron It was difficult to use an old Windex bottle to spray stuff through the tiny vent openings below the windshield. I didn't remove the cabin air filter. But after recently replacing my blower motor, and seeing a lot more of how things move, i would take out the filter, and spray directly into the place where the filter does - directly into the fan blower. But i sprayed as much as i could stand; about a quarter of a windex bottle. – Ian Boyd Jan 28 at 15:15

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.