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Air Conditioning Smell Funky?

A/C System Explained & HowTo Fix The Stink

Alright so today on Repairs101 I thought I’d talk to you about that awful funky smell coming out of your car’s air conditioning. If you live in a warm climate or a particularly humid climate you’re going to have a problem like this. It arises every the first few minutes when you first start up your vehicle and you turn on your air conditioning. The smell comes out. It smells like a wet dog or an old pair of work socks or some sweaty guy’s work-boots. Or maybe some gross old carpet.


Alright so today on Repairs101 I just thought I’d talk about how every summer somebody asks me – what’s that awful smell coming out of the air –conditioning in their car? It’s fairly common and it’s surprisingly easy to fix.

Basic A/C components

OK so I made this 3D cutaway model using Google’s “SketchUp”. To try and help represent how the major components of the air conditioning system are laid out in the car. More or less. The condenser is up front. The evaporator is hanging on the firewall right in front of the cabin. The compressor’s on the engine somewhere. And then you’ll have your expansion valve or orifice tube located usually right in front of the evaporator.

OK now I got this image from my John Deere “Fundamentals of Service” textbook. They’re excellent books.

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Air conditioning theory

OK so it’s going to come into the compressor as a low pressure gas. The low pressure gas is going to get compressed into a high pressure gas. The high pressure gas will go into the condenser and become a high pressure liquid. The high pressure liquid gets through an expansion valve then and becomes a low pressure liquid. Which then flows into the evaporator to become a low pressure gas and in doing so becomes exceedingly cold.

The blowers blow the warm air from the cabin over top of the evaporator. They do a heat exchange. The hot air molecules are picked up by the refrigerant. And then piped back into the compressor to start the cycle all over again. Here’s a schematic representation.


In your face

So when you turn on your A/C the blowers move the cabin air over the evaporator. And pick up a funky smell that’s the result of a microbial growth. It’s a mould or mildew or a fungus that’s growing on the evaporator and that’s what that smell is. If you’re blowing that smell in your face I’m afraid you’re blowing mould in your face. Dirt and dust and organic material collect on the evaporator as the result of getting past that intake screen. Now the evaporator itself is a moisture magnet. So you’ve got this dust and dirt and organic matter all combining with a very, very wet environment. So it’s the perfect breeding ground for mould. OK so the question would be… Is there anything that you can do to prevent this from happening to your vehicle?


And the answer is yes, there is actually. What you do is when you’re out driving and you’re using your air-conditioning. Just before you get to your destination, you know, a couple of blocks. Turn off the air conditioning. Switch it to vent. Leave the fan on full and try to use the blower to dry the evaporator before you park your vehicle.


I’m going to use this product here, “Clean Air”. It’s a little more expensive than just using an ordinary room deodorizer. Or certainly vinegar and water would be the least expensive option.

If you’re living in a really hot and humid environment. Where your A/C is running Full Tilt Boogie all the time. Then you’re going to be doing this quite often. And you might want to just use something inexpensive like an ordinary household disinfectant like “Lysol”. If you’re sensitive at all to smells or chemicals. You might just try a mixture of water and vinegar shot out of a solvent sprayer like this one.

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