What is that terrible musty/mold smell coming from my air vents?

There have been numerous complaints of a bad musty/mold smell coming from the air conditioning vents. This usually occurs after the A/C has been running or after the truck has been sitting.

Here are some potential fixes as told by our members in the forums:

• It is a good rule of thumb to shut the a/c off a minute or two before you shut the engine off to clear it of any "cold" air left in the system. The problem is that the "cold" air that has not blown out will condensate in the vents and will have a musty smell over time. You can also try to run just fresh air through the vents to clean them out a bit.
• If the smell is only there on Fresh Air vent, remove the wiper arms and plastic cowl panel, that is where the fresh air comes from. very possible something crawled up and died in there,have seen this several times, if you do not find anything, spray Lysol in this area profusly!!!! and see what happens!
• auto parts stores has a spray for that, i sprayed mine and smell went away
• 2005 F-150 Mildew Smell - I had a problem similar to that, just my passenger side would get wet. Ended up being a drain hose for the A/C unit wasn't long enough and at highway speeds it was allowing the water to drain back into the cab. I brought it back to the dealer and they took care of it for free.
• all i can suggest is make sure you drain for your A/C is free of debris, then ask around at some auto parts stores for products that are used to eliminate A/C odours. Ford has a special chemical used in a spray bottle in which you need to remove part of the plenum to spray this chemical on the evaporator. Some other products ive used is an aresol can you set in the vehicle and open the can setting your A/C on max and letting it circulate for 15 minutes with all windows shut and all that it seemed to do the trick.
• First turn the heat on and let it run, then let the air run. He [dealer] told me not to always leave it on MAX a/c, and make sure when you shut the vehicle off, to turn the knob from MAx a/c cause that shuts all the vents off, and it gets no fresh air. I tried it and it worked, no smell no what so ever. So it came out good in the end.
• Well, the smell came back with a vengeance... The air conditioner drain was only going through the firewall about a quarter of an inch. Everything under the rubber mat (no carpeting) on the passenger side was soaked. They put in a new a/c hose that actually exited the vehicle, rolled back the matting, sucked up all the water they could, deodorized it, and let it set with a fan running on it for two days.
• It could be from the air conditioning.. They can get musty smelling from mold growing on the evaporator. The evaporator is always wet when the AC is in use. If the drain under the evaporator gets plugged, then water can sit in your plenem and breed nasty stuff.
• One of the primary jobs of an a/c system is to remove moisture from the air before that air comes into the cabin of the vehicle. However, in more humid conditions, sometimes the a/c system cannot remove all of the moisture and when that happens, that moisture gets cooled down just as the air does. When that happens, it will come through the vents as a mist or a fog. It is nothing to be concerned about. It does not hurt the a/c system and it does not mean that there is anything wrong with the a/c system. As far as the smell coming from the a/c system, if it is a mildew smell, then it is from mildew building up in the a/c evaporator case. That will occur if moisture stays in the evaporator case too long before draining out through the drain tube that comes out under the right side of the vehicle. There are several ways to get rid of it. You can have a technician remove the evaporator and clean it thoroughly, but that costs money. A cheaper way that will, in many cases, get rid of the odor is the following: 1) Park the vehicle outside with all of the windows open. 2) Run the engine with the a/c on and on the fresh air setting (setting where outside air comes into the vehicle). 3) Turn the temperature control all the way to hot. With the a/c on, it will force air through the a/c evaporator but with it being hot air, it will help to dry out the inside of the a/c evaporator. When you do this, you can also spray a small amount of Lysol into the air intake just in front of the windshield. That will also help to kill the mildew inside the evaporator case. Normally, you would need to run the engine and a/c for about 2 hours to reduce the smell. If it is a sweet type smell, then you may have a heater core leaking and if that were to be the case, the only repair would be to replace the heater core, which, depending on the year and model of your truck can be a little tough and you may want to have a professional technican replace it for you.

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