Why Your Car AC Smells Musty (And How to Fix It)

I want to show you some all-time records for high temperature. Does the air coming out of your vents now smell a little off? It's air conditioning season, and I'm getting a lot of phone calls about a musty, sour foot smell coming out of the air vents. And for all of you that are a long ways away and can't come see me to get this issue resolved, I'm going to show you what we do, and if you're handy, you can possibly do this at home to eliminate this problem. Anytime you run your air conditioning system, your evaporator is cold, and as that humid air runs across it, it's going to condensate. That condensate has to drip out of the bottom. Now, if you have contamination in there, such as dust, pollen, animal debris, hair, those things, when mixed with moisture, create bacteria, and that bacteria smells. And that's what that musty smell is that you smell as soon as your car starts up. Now, a lot of times, once the vehicle runs and that evaporator cools off, the smell will go away. But if you're tired of smelling that thing on initial startup, let me show you what causes it and how to resolve it. So this is one of our junkyard trucks. We're just using this thing because a lot of the components are removed, so it's very easy to see this. All these components on a fully assembled vehicle are very hard to access, a little bit harder to make videos of. So first, let's understand how the air conditioning system works. On the inside of the cab, on the firewall, you have your HVAC box, which is going to contain your evaporator and your heater core. What this does is when the vehicle is not on recirculate, it's going to draw air up here on the cowl. So there's an opening on every vehicle's cowl. It will draw air. And inside this pocket on this truck, you can see the ECM. But on the top right of that ECM, you'll see an opening in the firewall. That's where your fresh air goes in. So if you live in a dusty climate, you can see the dirt that accumulates inside here. It's also a common place for mice, rats, squirrels to build nests inside of. Whether your vehicle sits in the rain and that water gets inside of there or you go through a car wash, that's one possibility for that odd smell to get inside the cab. So when you have your recirculate door closed, this vent right here is going to roll up, which I can't move it because the motor is bound up. But this lid will roll back and it will close that air from coming in from the outside. It will draw fresh air from inside the cabin. If you have a lot of dust and debris up here inside your dash, that can cause a smell. But most of the time, the musty smell is going to be coming from inside this evaporator box. So what happens, that air goes down, it goes through the fan. And from the fan, it goes inside. It either goes through the evaporator or it goes through the heater core. So there's a drain right here. Every vehicle has one. You'll notice when you run your air conditioning, you'll see water dripping out on the ground. If your drain is clogged, that's one step in eliminating this problem. The water inside this box is going to drip and it's going to run down this drain and it's going to go out through the firewall. If that's clogged, you're going to sit with water inside this box. It will become moldy and mildewy and that will create a nasty smell. So we have a couple ways we can eliminate this. One is trying to keep the top of your vehicle clean up here. If you're going through the car wash, most of that stuff will rinse out. If you don't wash the vehicle very often, you get a lot of dirt accumulated. You may need to stick an air hose in there and try to blow some of that stuff out. This one has a small access opening here underneath the cowl. But there's not a whole lot of space to get inside that. You can see that under here, there is no access all the way across this. Now, do know that your ECM is inside there. So don't try sticking a power washer up inside that cowl because you could damage your ECM or other electronic components. But step number one, make sure that your drain is not clogged. They normally will have a little nipple that elbows down. You can squeeze that nipple and make sure that water is flowing out. If there's mud inside there, you may need to stick a pick or a screwdriver in there. Get some of that mud knocked out. And if your cabin filter is dirty like this, that's one step in eliminating a smell, is getting rid of this dirty, musty-looking cabin filter. So why face forward? We use the Fridji Clean, Fridji Fresh. This gives us a can that we can spray inside the air vents and on that cabin filter to remove bacteria. This one goes inside the air box on the evaporator. So there's a couple ways you can get this into the truck. If you want to do this yourself at home, the easiest way, you can climb up underneath the truck. You hook that can, and you run this small tube up inside the drain right here, and you get it as far up inside the evaporator box as possible. You run the air conditioning on high, kick that fan all the way on high, and then you just unload until that entire bottle is through. It'll go through, cook that evaporator, kill all the bacteria. The more efficient way to do it is to get as close to that evaporator as possible. And so we will actually drill a hole here in the box, and we'll install a Schrader valve, which is what I have on my truck. So we'll go back into the shop. I'll hook up and show you how this process actually works. So there's a few different ways you can access your evaporator so that you can apply the Frigifresh inside. And depending on which model of vehicle you're working on, one way might be easier than the other. We're going to talk about a few of them right here. So on a four, we're going to press the two tabs. You'll remove your retractor clip here, drop down the glove box. So inside here, you have one access. It'll be by removing the cover here for your cabin air filter. I've done this before, so I actually have a Schrader valve installed right here, which is the easiest way to do it. If you plan on doing this in the future, you simply just drill a hole. That thing will thread into the box, and then you have a permanent way to access this for annual cleaning. So we're going to pop that Schrader valve cap off here. Go ahead and fire up the truck for me, John. So what we'll do is thread this up underneath. It's a little bit of a contortion trick to get this thing on since you're a little blind, but we'll thread it on just like we're inflating a tire. I now have that installed just like that. Okay, so now what we're going to do is attach this to the can, and we're going to kick the AC all the way on high, put the fan on high. Make sure the temperature is cold so that it is running it through the evaporator. On auto, depending on our temperature, it may only be running it through the heater core or be blending a lot of warmer air. So we're just going to go ahead and hit this. So you can audibly hear a difference. So this thing is creating a bunch of foam. That foam is going to go through and completely coat that evaporator, and then the excess liquid should start draining out the bottom of the evaporator drain. So it has restricted the air because what this is doing is completely foaming over that evaporator. So right now my airflow is quite restricted. It's going to take just a minute. What will happen is that evaporator is cold, it's going to condensate, and essentially this is going to rinse everything off of that evaporator. I'm going to go ahead and pull my line off. We're going to just let that run for a little bit. So you can tell that box is full of foam. You can see it dripping out right there. Looks like I've got a little bit more dripping out by the fan. We're going to let that run for a minute. It should start coming out the bottom here. So you can see the foam coming out underneath. So I haven't gained much airflow back. It's still fairly restricted, but slowly starting to come back. Basically everything on that evaporator is going to rinse down. It's going to condensate. All that junk inside there is going to come out and come down the bottom of the drain. Now, if you do have the nipple on your drain, make sure and pop that thing off so you have good flow, so the foam can gravity flow right out the bottom of it. If you have the factory nipple still on there, it's somewhat pinched closed to prevent airflow going reverse of it. That can actually cause a restriction and it won't drain out quite as fast. And we're slowly starting to gain airflow back. And then we have a little can right here that if you're not replacing your cabin air filter, you can spray that air filter down. Or if you have smells inside the vent, you can spray those vents down. And this will be one last little bacteria killer to make that AC smell fresh for you. So now we're starting to gain a lot of airflow back. So it's been about a minute, maybe two minutes. I had a little bit of foam leak out inside, but let's go look underneath. You'll probably see a lot underneath the truck. So there's still quite a bit coming out. You can see the color. It's kind of a brown foam. So I replaced my cabin air filter every time I do an oil change because it's so dusty in our area. You can see even as clean as I keep my truck, how dusty it is underneath the dash. That's what type of air you're running through that system. So keeping that cabin filter clean and changed out often is very important. So if you don't have access to buy a kit like this, your other option would be just go get a can of Lysol or some type of disinfectant and spray it inside of the air box. You can take your cabin filter out, spray it down in that box. That's going to help. It's not going to clean as well as this does because this foaming action will actually build up on that evaporator and from top to bottom with gravity help pull that debris off. But we're already back to a nearly 100% airflow. So what we're going to do is let this thing keep running for about 10 or 15 minutes until I don't see any more foam coming out the bottom. As it condensates, it's going to go faster. So we're in a dry, arid climate and so it's very common to get dust inside that system. So what I'm rinsing out is dust. Now if you live in a humid environment, you're probably going to have a lot more bacteria inside there. It's going to be creating that smell. Your rinse may go a little bit quicker because the humidity, you're going to build up water quicker than we do here in the panhandle. It is probably close to a relative about 10% humidity. So the amount of water that condensates inside my box is much lower than other places in the country. So the timing of this, the more humid it is, the quicker that rinse is going to go. If you do decide to install this Schrader valve yourself, there is a carpet shield right underneath the dash that is very easy to pull out. You can pull your trim panel, pop that piece off, and you have direct access to run a drill bit right up inside that box. So this is a common issue that I see across all manufacturers, especially in the springtime or late in the summer. When you first start using that AC or after you've used it for a long time, a bunch of you followers had reached out asking what you can do to eliminate this smell. 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