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Discussion Starter · #1 · (Edited)
I sometimes drive by my local sewage treatment plant in my 17 MDX. I would always make sure I was on "Recirculate" when I'd go by to stop the smell (mostly) from coming in. Lately, even when on "Recirculate", I really smell the odors. Enough to make me question the operation of the inside/outside diverter valve. I have sped up the fan, muted the radio, and flipped between Outside and recirc and can hear a SLIGHT difference in the sound of the fan. The difference in sound used to be more pronounced in past times when I would switch back and forth. Anyone have any suggestions as to properly check this matter out? Has someone out there had this same issue?
 

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I have the same issue when passing dairy farms in eastern New Mexico and west Texas. Using Recir helps; but, still get a slight whiff of the good stuff. I usually have to roll down the windows for a few seconds to clear out the cabin air once I clear the area.
 

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2018 MDX SH-AWD Tech package
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When is the last time you changed the cabin filter? Charcoal cabin filters should help.
 

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Have you checked to see if the recirc is really working? What that really does (on most vehicles) is move a door in the plenum to block the outside air and send the inside air as the input to be cooled. It's not that unusual for these doors to get sticky and no longer flap back and forth smoothly or completely and it's also possible the motor for it failed. I haven't looked at what's done in the MDX specifically but a failure in this area on vehicles isn't unusual.

The recirc function not working will also make your vehicle take longer to cool down on a warm day and will make the a/c work harder to maintain the cooler temps. Have you noticed a problem with the cooling not working as well as it used to?

If the recirc is properly flipping that door back and forth then you're just getting the whiffs of some outside air that's leaking in from various leaking points, like the rubber window seals, etc.
 

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Discussion Starter · #6 ·
When is the last time you changed the cabin filter? Charcoal cabin filters should help.
I did replace the factory non-charcoal filter about 10k ago with an aftermarket charcoal one, and IS due to be checked, but still doesn't explain how smelly outside air is getting into the car while on Recirculate mode. No outside air should be coming in while in recirc mode. I understand there can be SOME leakage, but the stench is REALLY coming in.
 

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Discussion Starter · #7 ·
Have you checked to see if the recirc is really working? What that really does (on most vehicles) is move a door in the plenum to block the outside air and send the inside air as the input to be cooled. It's not that unusual for these doors to get sticky and no longer flap back and forth smoothly or completely and it's also possible the motor for it failed. I haven't looked at what's done in the MDX specifically but a failure in this area on vehicles isn't unusual.

The recirc function not working will also make your vehicle take longer to cool down on a warm day and will make the a/c work harder to maintain the cooler temps. Have you noticed a problem with the cooling not working as well as it used to?

If the recirc is properly flipping that door back and forth then you're just getting the whiffs of some outside air that's leaking in from various leaking points, like the rubber window seals, etc.
Yes, it doesn't seem as cold on the real hot days and the blower fan is running at rather high speeds to try to compensate. This is why I've been shutting off the radio, turning the fan speed all the way up and then manually switching back and forth between outside and recirculate because when on recirc, one hears the fan much more than when on outside mode. I DO hear a difference when I switch, but doesn't seem nearly as much difference in noise levels as there used to be. I gotta pull that cabin filter and check the condition of it.
 

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I’d pull the cabin air filter out and see if you can spy on the recirc door from the filter opening, maybe with a small mirror or camera.
 

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Discussion Starter · #9 ·
I’d pull the cabin air filter out and see if you can spy on the recirc door from the filter opening, maybe with a small mirror or camera.
Great suggestion. Gonna (if I get some time) get to the cabin filter tomorrow and I do have technicians' mirrors that I can use.
 

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Drove behind a Chevy Express on the Turnpike last night, and some smoke was coming from its trailer; lets just say it came into the cabin and smelled like rubbish. Also, some stretches of the FL turnpike smells so bad, even with recirc that stench comes into the cabin.
 

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Discussion Starter · #11 ·
I took out the cabin filter, saw that it wasn't very dirty, shook it out and put it back in. But when I had it out, I could not get near or see the recirc/inside air door. Beneath the filter is an enclosed fan blade that I cannot see past and saw nothing of note above the filter. I tried the sound comparisons while I had the filter out and again, did not hear much (heard some, though) difference in sound between recirc and outside air. Buttoned everything back up with no conclusions.
 
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