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Why does my air conditioning stink when I first turn it on?
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What causes it?
How can I get rid of it?
How do I prevent it from happening again?

What causes it?  back to top

That's mold and mildew in the A/C evaporator drain pan, the pan's drain hose, in the evaporator or its sealing gasket. It could also be rotting leaves and other organic debris in the pan itself.


How can I get rid of it?  back to top

If it's the gasket, that's tricky, as the evaporator is not easy to get at. This excellent PDF has more info:
http://refrigerants.dupont.com/Suva/en_US/pdf/macs_200404.pdf
(go down to Evaporator Odor - What to do Now?)

However, Toyota has a kit for this problem (PN 00050-00008). It involves drilling a small hole into the evaporator box, installing an adapter, then using the supplied spray can to fill the evaporator box with disinfecting foam. The foam eventually collapses and runs out the drain hose. Apparently this works very well. I assume the kit would work for Hondas as well, since the A/C system will be basically identical from make to make.

The drain pan is easier to deal with. (It's a good idea to check the pan itself for leaves, pine needles or other rotting organic matter. If present, it will need to be physically cleaned out. Disinfectants won't work on that.)
Often the mold plugs the evaporator drain pan's drain hose (that's what drips on the road as the AC runs) and the water can't drain properly, leading to stinky fungal growth. To remove the smell, you need to remove or kill the mold and mildew. So, short of ripping your dash apart to scrub everything clean, what can you do?

A coat hanger or other poky-type tool might be needed to probe the drain hose to open it up first, then...

One answer from from Mike Pardee:
"It's such a common complaint with so many cars I am surprised there aren't any great kits on the shelves to take care of it.
"The most comprehensive treatment I've seen described (haven't had occasion to try it) involves connecting a basketball pump to the evaporator drain tube. The pump is filled with rubbing alcohol or straight isopropyl and the alcohol is flushed backward into the evaporator drain pan. The OP had us fill the drain pan until it ran over and then let it sit a minute or two.
When the pump is removed, the mostly disinfected drain pan contents are flushed out.

Gleaned from rec.autos.tech is this, from the respected HLS:
"If you can spray in a chemical to kill that fungi, chances are you can kill the smell.  The tubes need to be open so that drainage can take place. One of the products that you might get your hand on is Consan Triple Action 20.  It is based on quaternary ammonium compounds that kill a broad spectrum of germs, bacteria and fungi.  At use concentrations it shouldn't be particularly corrosive to skin or aluminum, but you wouldn't want to leave the concentrate in contact with either.
A dilute spray of Lysol might also turn the trick.  Some people like the odor, others don't.  Same caveats about usage. The OP indicated the overflow dries quickly without harming the carpet, but I think I'd fold an old towel in the passenger floor at least."


How do I prevent it from happening again?  back to top

And a closing forehead-smacker from gfulton, in reply to HLS's message above:
"If you'll shut the a/c off about a mile from home and let the evaporator dry out, the problem won't reoccur."

Now why didn't I think of that?

Finally, it seems that current production Volvos run the A/C fan for a while after shutdown in order to dry out the eveporator and prevent mildew.