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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:

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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?

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2 Answers 2

up vote 2 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.

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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.

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