What can I do to prevent my air conditioner from smelling moldy as the temperatures begin to rise?

Every year someone I know or myself begins to get an odor from their air conditioner that's musty or moldy when the weather begins to get warm.

I've never tried preventive measures to ensure this does not occur.

I've also looked through the questions on this site and cannot find a duplicate. I can only find questions related to how to respond once you have the odor.

Can someone share some ideas regarding this potential problem?

Are there any methods I can employ that are effective at preventing this from occurring this year?


3 Answers 3


You need to prevent the buildup of mildew in the system during the colder months, as that's what causes the smell.

One trick I've heard is to make sure you run the A/C regularly (at least once every couple of weeks) during the cooler period, so that any spores get blown out of the ducts before they get a chance to settle and grow - a useful side effect is that this also keeps the seals lubricated and so increases their lifespan.

Have a look at http://honestjohn.co.uk/faq/air-conditioning

  • what seals?....
    – Moab
    May 16, 2016 at 13:42
  • 2
    On two different cars one had the A/C on the whole year, because of windows fogging up, the other doesnt need it. The car with the A/C always on never had smell problems, the one that uses it only in summed did. Started turning the A/C on every so often in that car too, even if not needed, and never happened again. May 16, 2016 at 15:10
  • @Moab the various o-rings in the system that stop all the refrigerant from escaping - the refrigerant contains lubricants.
    – Nick C
    May 16, 2016 at 15:20
  • see honestjohn.co.uk/faq/air-conditioning
    – Nick C
    May 16, 2016 at 15:21
  • @NickC that needs to be in your answer
    – Moab
    May 16, 2016 at 18:28

One trick that has worked well for me in preventing the musty smell is to turn the A/C off but leave the blower on about a minute or so before reaching your destination (if you are going to be parked for a while). It seems this allows accumulated moisture in the system to be removed before shutting the blower down.

  • I was told this long ago. I tend to do it, but you have to form a habit to remember.
    – user15009
    May 16, 2016 at 22:44

I suggest using DampRid or similar desiccant. You essentially put a container, (usually supplied with the product) in the car in a inconspicuous spot. It pulls quite a bit of moisture from the air. This dries out the ducts and vents and will reduce mold build up.

Don't put it in the vents. You put it under a seat, or in the truck depending on how your car is. It can pull an amazing amount of moisture out of the air, and even a minor change can totally eliminate mold buildup. Do keep it in the jar/jug/container, don't spread it around. It won't hurt much if a little is spills, but a lot of it will ruin your carpets.

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