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Activated carbon cabin filter: carbon side up or down?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Josh Lyman, Jul 27, 2017.

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  1. Josh Lyman

    Josh Lyman Junior Member

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    Air flows from top to bottom, and orientation doesn't matter for paper-only cabin filters. FRAM has admitted that aftermarket filter orientation is inconsistent and often incorrect. But that's not what I'm here to talk about.

    If your cabin filter has activated carbon on one side, should the air flow into or out of that side? Conventional wisdom says paper side first so it can catch large debris, letting the small odor particles get captured by the carbon side on the way out. However, this only makes sense if you have a multi-stage filter with space between the stages, neither of which applies to cabin filters.

    I've also seen people say that having the paper side first allows dirt to collect on it, leaving the carbon side "cleaner" to collect odors, but the filter media is so thin that any dirt on the paper side would block the carbon directly behind it from cleaning the air passing through.

    Finally, since the filtering compartment isn't airtight, odors would be able to collect onto the paper and disperse without being captured by the carbon.

    However, if the carbon side comes first, odors are adsorbed directly into it, the only reason you got a activated carbon filter in the first place.

    Thoughts?
     
    #1 Josh Lyman, Jul 27, 2017
  2. bisco

    bisco cookie crumbler

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    is there no flow direction arrow on the side? is it a toyota?
     
    #2 bisco, Jul 27, 2017
  3. Josh Lyman

    Josh Lyman Junior Member

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    There is, but that arrow doesn't matter because FRAM has admitted to their arrow pointing in the "wrong" direction. Some people have said customer service told them to install with the carbon pointing up and others have ended up with the carbon pointing down.

    I'm trying to bypass the apparent stupidity of everyone involved by determining scientifically which orientation is better, regardless of marketing fails and incompetent arrow printing.
     
    #3 Josh Lyman, Jul 27, 2017
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  4. bisco

    bisco cookie crumbler

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    maybe take a look at an oem, they likely know what they're doing.
     
    #4 bisco, Jul 27, 2017
  5. Currahee

    Currahee Member

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    I thought the Gen 2 filter could only be pointed one way; one side is flat and wedged into the plastic tray.
     
    #5 Currahee, Jul 27, 2017
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  6. bisco

    bisco cookie crumbler

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    that's the great thing about fram, the flexible design allows you to install it incorrectly. plus, they fit so poorly, unfiltered air is allowed through.(y)
     
    #6 bisco, Jul 27, 2017
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  7. jzchen

    jzchen Newbie!

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    I accidentally put mine in the wrong way on our '12 v. I have several Fresh Breeze filters for different vehicles, and decided to compare it with the others.

    I believe arrow points up IIRC. Does it say "UP"?

    I won't get home until Aug 9 to check I'm afraid.
     
    #7 jzchen, Jul 28, 2017
  8. jzchen

    jzchen Newbie!

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    Fram has a dose of baking soda as well. We use baking soda in our refrigerator for odors....

    Mann Frecious Plus has a polyphenol layer for alergenics. Learned about the line somewhat recently...
     
    #8 jzchen, Jul 28, 2017
  9. Josh Lyman

    Josh Lyman Junior Member

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    Not a bad idea, but either Toyota's carbon filters have carbon on both sides or they also can't decide if they want charcoal up:
    [​IMG]

    Or charcoal down:
    [​IMG]
     
    #9 Josh Lyman, Jul 29, 2017
    Last edited: Jul 29, 2017
  10. bisco

    bisco cookie crumbler

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    hmm, maybe they impregnate the whole thing.
     
    #10 bisco, Jul 29, 2017
  11. xliderider

    xliderider Senior Member

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    I put the carbon side on the "clean" side.
     
    #11 xliderider, Jul 29, 2017
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  12. CoastRider

    CoastRider Active Member

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    I only use Toyota OEM filters. A couple extra bucks is not going to break the bank. And it has an arrow on it that tells you which way is up.

    Better yet, I just keep a can of Febreze in the car. :)
     
    #12 CoastRider, Jul 29, 2017
  13. jzchen

    jzchen Newbie!

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    I'm concerned with carbon flowing into the air tunnels...

    But, OEM UP means UP, and I think Fram followed that, opposite to flow, which are the way most arrows are pointed. (It took me a few months at least to think to try and compare with the others I had). One surface of the Fram is white. One on the Frecious Plus is yellow.
     
    #13 jzchen, Jul 30, 2017
  14. jzchen

    jzchen Newbie!

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    Pictures sometimes aren't clear. I usually switch the OEM one for the Fresh Breeze or (now that I know about it) Frecious Plus. But some mention is made that they are not really effective and do seem to decrease flow. At least with the Fresh Breeze, I can somewhat notice it. Not using the car with the Frecious Plus much, but didn't notice decrease of flow the little I did.

    Even with the OEM Toyota filter, one side seems lighter than the other, no?
     
    #14 jzchen, Jul 30, 2017
  15. Josh Lyman

    Josh Lyman Junior Member

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    If that's true, that still doesn't help the rest of us who only have 1 carbon side. :(
     
    #15 Josh Lyman, Jul 30, 2017
  16. MattStevenson

    MattStevenson Member

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    #16 MattStevenson, Aug 1, 2017
  17. jzchen

    jzchen Newbie!

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    Let's resolve this now, as I have been a Fram Fresh Breeze customer for a while. (Even bought a big one for an '08 E90).

    Fram is consistent, and here's the proof. I have two in stock:[​IMG]
     
    #17 jzchen, Sep 25, 2017
    Last edited: Sep 25, 2017
  18. jzchen

    jzchen Newbie!

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    The HEPA one looks like something for me to look into as well....
     
    #18 jzchen, Sep 25, 2017
  19. jzchen

    jzchen Newbie!

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    This is the side air flows out, clean side:[​IMG]
     
    #19 jzchen, Sep 25, 2017
  20. sumguy

    sumguy Junior Member

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    Just changed mine, the old filter has an UP arrow. The new one has an arrow stating air flow direction. Can anyone clarify air flow direction for me? I'm guessing it may not even matter since its all paper
     
    #20 sumguy, May 25, 2018
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