Here is Dallas it is often over 100° in the summer and also quite humid at times (Right now 91° but only 15% humidity). I have always used the HVAC in AUTO mode to automatically alternate between recirculating interior cabin air and bringing in outside air while still 'conditioning' the air. I think it does a great job if you just leave it alone. The Lexus HVAC is quite a complex system and highly intelligent so you don't need to manually be altering or changing settings. The time when it most often alternates between the two (recirculating interior cabin air vs bringing in outside air) is when the cabin air temperature is very close to the same temperature as the outside air. However, during times of extreme heat inside the cabin (130+°F) like when the car is first started after it has been sitting in the sun, or when the inside temperature is set much lower than the outside temperature, the HVAC will not alternate as often but it still conditions the cabin air nicely with cooling air and lowered humidity based on your temperature setting. It seems the people that have an odor problem in their HVAC are the ones that refuse to let the HVAC do its job automatically or use the recirculation mode about all the time instead of letting the system take care of it automatically.

 

What I have learned in the past couple years of ownership is that smell only returns when I have it on auto mode. The auto system may work well in most climates but in a consistently hot and humid climate, it needs some manual input to keep it smell free.

 

I don't know about that! I'm sure Lexus has done extensive tests of their HVAC system in all sorts of climates, conditions and situations. I'd be inclined to think it's best to use the HVAC in AUTO modes.

 

​​​​​​Take a look at TSB L-SB-0003-20 where Lexus specifically advises the driver to take manual control of the hvac system:

"Advise the customer to set the HVAC system to the outside (fresh) air mode when parking the vehicle to assist in the reduction of odors that could be trapped in the HVAC system."

 

I find this to be odd advice.

Do you have any thoughts on exactly what setting the HVAC system to the outside (fresh) air mode when parking the vehicle actually does to assist in the reduction of odors that could be trapped in the HVAC system? When parking the vehicle the vehicle's HVAC system is turned off and not operating. It seems to me that the trapped odors would still be trapped inside a system that has no (zero) air flow whatsoever, which the way I see it is a stagnant and damp environment that would make matters worse, not better.

 

farimbithe - Do you have any information on how long prior to turning the vehicle off it is recommended that the air conditioning system be set to outside air mode? I wonder, is it 5 minutes or an hour or something different. The devil seems to always in the details, and the details clearly seem to be missing...

 

The tech that serviced my AC said 10 mins before arriving but I always forget to do it.

 

I do know that with all the Lexus and other cars I have had. The way I set it has had me never had the musky, mold smell problem.

Lexus does tell you to set it the source of incoming air manually and use auto. Also FYI - The smog Sensor setting does not work very well if you are not using a clean Lexus factory Charcoal filter. When used it works very well

 

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The evaporator core gets pretty cold during normal operation and like any cold item in a warmer environment, moisture in the air will condense on the surfaces (like a cold can of soda).

When the car is turned off with the cold evaporator, the moisture lingers there and microbes grow in it, causing the smells. That's why the issue is worse in continuously high humidity environments.

By introducing outside, ambient air (or even better, heat) the evaporator returns to ambient more quickly and the lingering moisture can evaporate more quickly, this eliminating the environment for microbes to grow.

If you already have a smell, it's unlikely that this specific action will eliminate it, thus the need for the cleaning procedure which involves flushing the evaporator with alcohol to kill any lingering microbes. This is more of a maintenance procedure once the initial chemical cleaning is complete.

 

Some cars get it and some don't, what you are doing with the outside air intake obviously helps either way but it's specific combination of climate factors (heat and humidity), it's duration, it's intensity, driving/use habits and maybe even where the vehicle is stored (mine is garaged at home and work for example).

I don't believe I have noticed a smog sensor difference when I last changed to the OEM charcoal filter but I'll take note of that next time I change it to see if that helps with the auto-switching.

 

5-10 minutes is all you need. If I'm up for a specific level of torture on my ride home, I'll blast the heat when driving home on a Friday when I know the car will be sitting until Monday.

 

Something tells me that Lexus does not expect owners/users of their vehicles to drive the last 10 minutes of their commute in Florida's heat and high humidity with the heat on! Or in Dallas or Phoenix when the temperature is 105°.

Competitors of Lexus should use Lexus' recommendation against them that owners should manually change the HVAC to outside air before parking the vehicle to help prevent bad odors from the system. So much for the word 'automatic'.

 

I'm doing a cabin filter test right now on my GS and will report back with the results.

Basically, I'm comparing the 87139-30100 and 87139-YZZ38 filters.

My car had the 87139-30100 for 10K miles and I did not get any smell, then I switched to the 87139-YZZ38 filter and it smelled after 2-3K miles and when I took it out, the filter smelled really bad. I replaced it again with a new 87139-30100 filter and we'll see.

I noticed that the 87139-YZZ38 filter felt cheap and very thin and flimsy. This filter is cheaper than the 87139-30100 ($27 vs $40) and both are charcoal and can be bought at the dealership but the 87139-30100 filter is beefier and feels like better quality materials.

 

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