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Why does my air conditioner have a musty smell?

Question posted by Jeremy W. regarding his Toyota Land Cruiser.

“I am writing into your repair mechanics to find out what is causing my air conditioner odor? My air conditioner has a musty smell that is typically noticeable for the first 60 seconds or A/C operation. After that duration it dissipates.”

Why does my air conditioner smell musty?

Your car air conditioning smells bad because you probably have mildew or bacteria in the air conditioning system. We deal with the air conditioner smell often and will explain why it happens, how to clean the air conditioner and how to avoid it. This is not uncommon and has nothing to do with a leak in the A/C system but can cause you some discomfort from the smell and possible mold.

How did my vehicles air conditioner get in this condition and start to smell?

As the air conditioner begins to cool down, there are metal fins (the air conditioning evaporator core) that get ice cold. Just like a freezer these fins will build up frost. When you turn the air conditioning off, the fins will defrost and this condensation turns into water. The water will typically drain out of a drain tube to the outside of the vehicle.

In some cases dirt/dust/debris can clog the drain (especially if the vehicle is parked under a tree, bush, etc… and gets organic matter into the vents at the base of the windshield). When the liquid mixes with dust, dirt, tree leaves, and normal debris in your air conditioning vents – mold and bacteria begin to form. At this point you will likely begin to smell the decaying organic matter as well as the, leaves, dust, mold, and bacteria that is growing or decomposing.

Below is a picture of a clients evaporator core that was filled with organic debris causing the musty air conditioning smell:

I have this problem, how do I clean the smell and debris from my vehicles air conditioner?

Start by removing the air conditioning cabin air filter (if your car is equipped, it is usually located behind your glove box) from the air conditioning system.

Here is an image of a dirty vs. new cabin air filter:

Next, use a vacuum cleaner or compressed air to clear out any leaves, dust, dirt, or debris from the air conditioning box. (this may be better suited for a professional as poking a hole in your A/C system is an expensive mistake… especially if the dashboard has to be removed)

Once you have cleaned the area, it is time to decontaminate the air conditioning box and a/c evaporator core. There are many different types of cleaners that you can use but a simple mixture of bleach and water would work just fine. Note: whatever cleaner you choose, that smell will stay with the car for many trips so be sure you are okay with the smells. Also, keep in mind

Apply the cleaner with a spray bottle and use whatever cleaning instruments allow you to access the air conditioner box. Don’t use too much liquid during this process because the excess will go into the air conditioning fan motor.

At this point let everything dry. You can speed it along by positioning a fan toward to the air conditioning box. Put everything back, install a new cabin air filter and test the operation.

Simple maintenance tips to avoid the musty air conditioning smell:

As we stated in the first paragraph, there is no way to avoid the repetitive condensation build up from the air conditioning. The tricks to avoid the musty smell in your air conditioning system:

  1. Change your cabin air filter every 30,000 miles or two years.
  2. Clean off the leaves and botanical debris from the area between your windshield and hood.
  3. Run the heater for the last minute of your drive to dry out your air conditioning box.

We hope your learned a bunch about why your air conditioner smells bad and what you can do to avoid it! If you have further questions please contact A+ Japanese Auto Repair for assistance with your Air conditioning system.

Adam S.

A+ Japanese Auto Repair - San Carlos Auto Repair - Ask A Mechanic.

A+ Japanese Auto Repair Inc.