I’ll share my experience with two M3s that have had the smell on and off, just so you have a better idea of what’s going on.
Under the frunk, there is a large opening on the left side close to the windshield. This is the air intake for your AC. If you stick your hand in as far as it will go, you’ll feel a metal grate in the back. You’ll also notice a small hole at the bottom, this is to drain any rain/car wash water that runs in (I’ll come back to this later).
Beyond the metal grate is your AC fan, then your filter, then the evaporator coils (the part that gets cold). The air flows into the intake, past the grate, through your filter and over the coils.
Now, to your problem. As others have said, the filter wouldn’t absorb moisture from the air, but it does likely wick water away from the condenser (the filter practically sits right against it). So both get (and can stay) wet. This is why Tesla recommends changing the filter
and cleaning the coils. This is also what they tried to solve for with the software update in 2020 that runs your fan after you park.
I’ve come to believe that this is not the whole problem however. I mentioned the drain hole in the intake earlier. There is another one inside the compartment somewhere under the filter and coils. This water all drains to the same place…on top of the aero shield on the bottom of your car (if you look under your M3, there’s a plastic cover that runs the length of the car…this is the aero shield). I posted a video below that shows what’s going on at the 23 minute mark (this lady removed her frunk assembly to troubleshoot the smell). If water is just sitting there, it’s just a matter of time before it starts to stink.
My TESLA Smells New Again! (FULL TUTORIAL/ Exploring HVAC System)
In summary, you need the cleaning and a new filter. The cleaner will clean the coils, go through the drain hole and run out on top of the aero shield and take care of that if it is the issue. Tesla usually doesn’t good will this since filter changes are routine maintenance, but occasionally they do (it really seems to depend on who you talk to). You can also do it yourself. It’s not terribly difficult and there’s really nothing to mess up (I’ve done it 3 times on two M3s and I can assure you I’m not a car guy). If you get an inexpensive filter and a can of Koolit or Kilma Cleaner from Amazon it’ll cost you $30-$40.
I’ll also add that you can do a couple of things to help guard against the return of the smell afterwards:
- Don’t run recirculate all the time (as @jjrandorin said, you need to introduce fresh air to the system occasionally)
- Adjust your cabin overheat protection settings. Either turn it off or set it to “fan only” (leaving it on AC will never give your unit a chance to dry out, especially considering where you live).
- Occasionally run the AC on HI for 15-20 minutes (you can do this from the app). The heat/fan speed will help push any accumulated moisture out.
- If you park in a garage daily (I do), occasionally park outside on clear, sunny days. This has helped get rid of the smell when it is mild
Hope this helps. Good luck!
I watched your video and I like what you've done to diagnose the issues. My first culprit was also the filter touches the evap coil, but I too have observed it doesn't touch.
My 2019 LR has gone through 6 filters and cleanings already. The first 1 or 2 cleanings would last a while and the car would be smell free for months at a time. Of late, I've gone through 3 cleanings in the last 5 months, with the smell coming back in a few days, so the condition has worsened. I've used both Klima and Kool-It.
On my 5th cleaning, I sprayed 91% rubbing (isopropyl) alcohol into the vents and into the evaporator housing as well to try to kill mold and mildew that is causing the smell. Now one might say that spraying alcohol onto aluminum causes corrosion. Yes it does, but the reaction at room temperature over a few minutes would not be cause corrosion. Spraying the alcohol, drying it out, and then spraying Kool-It did not help. The smell came back in a week.
On my most recent and 6th cleaning (last week), I took a flexible camera to look into the AC and it was not full of mildew. This is a good sign as this indicates that water is not clinging to the walls prior to the filter. Certainly air that enters into the filter is likely not to be saturated and this is to be expected (except for when it's raining, when it's close to 100% relative humidity). This also indicates that water is not evaporating, clinging onto the walls, and causing mildew when the car sits after the AC is operated.
I also used Klima during the 6th cleaning and I found Klima to produce 3X the amount of foam per can of Kool It. It feels like 3X Kool It cleanings. However this did not help as the smell came back in 2 or 3 days.
I'm thinking that water is collecting at the bottom of the housing where it does not dry completely. In my case, it has gotten so bad, even the Klima and Kool-It cleaners can't get rid of it.
I am certain there is growth at the bottom of the housing or immediately after the evaporator in the duct/hsg the Klima/Kool It foam can't get too. when the air passes over the evap coils, dewpoint temp is quickly reached, the air becomes saturated and water condenses out of the air and collects at the bottom of the housing. I'm not an experienced HVAC guy, but I do have an elementary understanding of thermodynamics... but I'm thinking the housing / duct immediately after the evap coils can be pretty cold as well. Any water that already didn't condense out of the air has a second chance to further condense on the cold housing. Immediately downstream of the evap coil, the air is already saturated, so it's not going to dry the housing if it's wet. Thus mildew grows. (saturated air is air at 100% relative humidity... The air can't absorb additional water, thus an air and water vapor mixture exists).
Given that, there are two places where mildew can potentially grow
1. Bottom of the housing
2. Immediately after the evaporator coils.
I've read reports of people spraying Starsan (food service santizer.. phosphoric acid based) and Lysol that helped to get rid of the mildew. So I started to look into what are in those, including Ther. aside from Starsan, Turns out these are all pretty much the same as a mixture of ethanol, Aklyl, and amonium chloride. I also noticed that all of them warn not to use on aluminum... I believe this is so as these are formulated with ethanol that will corrode aluminum. However, for brief application at these cool to room temps, it's likely not an issue. My experience with Lysol is that it's really strong smelling. So I started looking for similar dis-infectants that were unscented. That's where I found Microban santizing spray (unscented at Target) and Thechem Incide (Home Depot). it also seems that Lysol does make an unscented spray as well, but might a bit hard to find. Theochem Incide and Starsan as marketed as mildewcide and fungicide, but I believe that Lysol and Microban should do the same thing as they have the same ingredients.
Next is, how to address the problem areas.
1. Bottom of the housing: Remove the airfilter and just spray the coils, the housing in front on the filter for good measure and just keep spraying the evap coils until everything is saturated. empty the whole can if you have too. We want the bottom of the housing to be doused with disinfectant and to kill the mildew / mold / whatever it is.
2. Immediately after the evaporator coils: You can turn on the fan to a low or medium and just keep spraying. This will suck the atomized disinfectant blow some past the evap coils into the housing and duct immediately after the evap coil. Wear a respirator so you don't breath and ingest it.
Now this is theoretical at this point. I will try it this weekend. The smell really bugs me and I'm in my car quite a bit.
Turning on the heat each day and turning it off to dry the AC housing is a lot of work. I'm also thinking of parking it outside for a few days to see if that helps. It's nearing 100 degrees in SoCal these days which means + 120F in the cabin. Coupled with NO A/C overheat protection and the windows vented, that should help dry the system.
Theochem Incide
Theochem Laboratories In-Cide, Ready to Use Disinfectant, Gallon 500158-g
Starsan Foaming Sanitizer
https://www.amazon.com/Star-San-B0064O7YFA-San-32/dp/B0064O7YFA
Microban Unscented
Microban Sanitizing Spray Unscented - 15oz
Lysol Unscented
Robot or human?
I'd be a leery of little using Starsan. The SDS sheet says it's ph Level is 1.
