@edwardcoast (edwardcoast) posted a new topic, subject "Allergies - Disabling car's automatic air intake feature?". It read:

   I'm not sure exactly what to call it. Older cars, if you turn on the fan, or AC or heat, you could select to have it intake air from the outside or re-circulate the air in the cabin of your car.
    
    I have allergies, very bad allergies, and almost all the time I keep the selection to re-circulate the air in the cabin. If I am driving out in the country or highway with almost no traffic I can allow the outdoor air to come in without a problem.
    
    Before anyone asks me, what happens when I am outside of my car, well, I'm not breathing the direct fumes from many cars and trucks like I do while driving in traffic so it isn't an issue.
    
    Is there a way to disable this? Such as cutting a wire to a sensor or whatever is making it automatically change on its own?
    
    I have driven many cars over the years including rentals and some seem to have this automatic feature while others don't.
    
    Is there any sort of solution to this other than buying an old car? I read in some manuals for the car, they allow you to override this by holding down a button and doing some magic, but this doesn't work on all car models.
    
    The other idea I had, is there way to upgrade the air filtering system in a car to give it a HEPA air filter? Has that worked for anyone with allergies?

To which @Gary_T (Gary T) replied

    All modern era cars I know of either have a dedicated button to choose between fresh and recirculated air*, **OR** automatically engage recirculation in the MAX A/C mode.
    
    If you will provide the year, make, model, submodel if applicable (e.g. LS or EX), and engine size, I can probably find out if the car has a cabin air filter. If it does, there might be a charcoal filter option or you might be able to fabricate a HEPA substitute. If it doesn't, it could range from fairly easy to nigh unto impossible to design and install one. There's a **LOT** of variation in how different manufacturers lay out the cabin air intake.
    
    As to bypassing the controls to keep it on recirculate, that could be a significant challenge unless you're quite familiar with this type of thing. Again, there are many different system designs, and you'd have to know how yours operates and what the access is to certain parts to figure out what to do. If it was successfully done, there could be a problem defrosting the windshield due to excess moisture buildup in the cabin when on recirculate.
    
    *Possibly this is only available with the A/C on.

To which @edwardcoast (edwardcoast) replied

    Gary_T:
    
    > …I can probably find out if the car has a cabin air filter. If it does, there might be a charcoal filter option or you might be able to fabricate a HEPA substitute. If it doesn't, it could range from fairly easy to nigh unto impossible to design and install one. There's a **LOT** of variation in how different manufacturers lay out the cabin air intake.
    
    Assuming there is a cabin air filter available for it, how is this installed? Is this something that the dealership could do when they are adding coolant to the AC system? Do you know where it is installed exactly? Thanks!

@edwardcoast (edwardcoast) replied

    edwardcoast:
    
    > Assuming there is a cabin air filter available for it, how is this installed? Is this something that the dealership could do when they are adding coolant to the AC system? Do you know where it is installed exactly? Thanks!
    
    I did some searches, I see. It could be under the glove box or accessible from under the hood.
    
    OK, I think I should be able to ask a car dealership's parts department if they have this and have them install it.
    
    I'm surprised the repair places don't ask if you want this done just to provide more service work.
    
    I hope this solves the problem. I wouldn't want to entirely disable the selection of outside air vs re-circulating the cabin air. Just the automatic feature.

After which, @bob_2 (bob++) added

    Every car I have owned since the 80s had a pollen filter on the cabin air intake and this is changed at each service. I don't know if there are higher grades of filter available.

Then @jz78817 (jz78817) said

    > I'm not breathing the direct fumes from many cars and trucks like I do while driving in traffic so it isn't an issue.
    
    how are you allergic to the “direct fumes” from other cars?

So @Gary_T (Gary T) replied

    edwardcoast:
    
    > Assuming there is a cabin air filter available for it, how is this installed? Is this something that the dealership could do when they are adding coolant to the AC system? Do you know where it is installed exactly? Thanks!
    
    How/where it's installed varies with different cars. I could tell you if I had the info I requested above.
    
    A/C systems don't use coolant (that's the antifreeze/water mixture in the cooling system – radiator etc.). They use refrigerant. Recharging the A/C with refrigerant and replacing the cabin air filter are totally separate operations.
    
    edwardcoast:
    
    > OK, I think I should be able to ask a car dealership's parts department if they have this and have them install it.
    
    If your car has this feature it came with a filter from the factory, so it should be a matter of replacing the old one. For your purposes, I think an activated-charcoal type filter, which is available for some cars but not all, would work much better than the typical pleated paper type.
    
    > I'm surprised the repair places don't ask if you want this done just to provide more service work.
    
    So am I. I'd say 90% of the cars I service that have cabin air filters are seriously past due for replacement. Here's a comparison of old vs. new. On most cars it's a fairly quick and easy procedure, and it's called for every 15K or 30K miles, yet it's very often overlooked. Beats me as to why.

After which, @edwardcoast (edwardcoast) added

    I found what looks to be a good source for Cabin Air Filters that are HEPA made by Bosch Auto Parts and are sold on Amazon.com.
    
    http://www.aftermarketnews.com/bosch-introduces-new-hepa-premium-cabin-air-filter-line-for-passenger-vehicle-applications/

So @edwardcoast (edwardcoast) replied

    jz78817:
    
    > how are you allergic to the “direct fumes” from other cars?
    
    Allergies Overview

To which @Machine_Elf (Machine Elf) replied

    jz78817:
    
    > how are you allergic to the “direct fumes” from other cars?
    
    It looks like diesel exhaust particulates are probably the culprit. Traffic-related pollution is present in higher concentrations near busy roadways, so it's not surprising that the OP breathes easier during pleasant country drives with sparse traffic.
    
    Given that the problem seems to be particulates, a HEPA filter with recirculation probably will offer some benefit.

@SmellMyWort (SmellMyWort) replied

    edwardcoast:
    
    > I found what looks to be a good source for Cabin Air Filters that are HEPA made by Bosch Auto Parts and are sold on Amazon.com.
    > 
    > http://www.aftermarketnews.com/bosch-introduces-new-hepa-premium-cabin-air-filter-line-for-passenger-vehicle-applications/
    
    Amazon also has a “My Garage” feature where you can put in your car's info and determine if one of those filters will fit.


{'source': 'discourse', 'url': 'https://boards.straightdope.com/t/allergies-disabling-cars-automatic-air-intake-feature/781758', 'title': "Allergies - Disabling car's automatic air intake feature?", 'views': 1614, 'has_accepted_answer': False, 'word_count': 1344, 'like_count': 0, 'reply_count': 10, 'participant_count': 6, 'posts': 11, 'tags': '', 'author': '@edwardcoast (edwardcoast)', 'participants': '@edwardcoast (edwardcoast), @Gary_T (Gary T), @bob_2 (bob++), @jz78817 (jz78817), @Machine_Elf (Machine Elf), @SmellMyWort (SmellMyWort)', 'image_url': [None], 'created_at': '2017-03-09T05:34:48.000Z', 'last_posted_at': '2017-03-09T22:24:25.000Z'}