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Merc Convert
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Discussion Starter · #1 ·
I've gotten some answers but it seems to vary on whether or not the arrows point down or up. If I look at the side of the Mann filters, the writing is oriented correctly with the arrow facing down, indicating air flows from the top, through the filter then into the cabin. If I turn it upside down, the lettering is upside down and the arrow is pointing upwards. I would think the writing on the filter would correspond with the way it is placed down into the filter box, e.g. not 'upside down'.

Does somebody have a definitive answer as to which way these Mann filter arrows should point? The instructions are terrible and my existing filters were placed arrow up on passenger side and arrow down on drivers side!! :dunno:

Thank you!
 

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Merc Convert
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Discussion Starter · #2 · (Edited)

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The air flows from top to bottom, and then into the car. Arrow points down. Ignore the writing.
 

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arrows should point up

Ok searched again after posting, found a bluebee post with this link, appears confirmation of arrow pointing up (as in towards the underside of the hood), yeah??

http://www.bimmerfest.com/forums/showthread.php?t=458513

But then this freakin link shows airflow towards the bottom?? WTF? (look at the diagram again....your assumption is incorrect)

http://www.bimmerfest.com/forums/attachment.php?attachmentid=194160&d=1248208081
The air flows from top to bottom, and then into the car. Arrow points down. Ignore the writing.
The arrows on the microfilters should point upward...and Bluebee's as well as the other illustration confirms this. :D

Look again (closely) at the illustration...the air enters the microfilter compartment and flows UPWARD thru the filter, then the "fresh" air flows FROM the top of the microfilter into the car's HVAC system. The arrows near the microfilter are curved upwards to indicate that fresh air is drawn into the BOTTOM of the microfilter's plenum first...then UPWARD thru the micro & carbon filtering media, then into the car's HVAC fresh air intake. This allows HEAVY objects sucked into the plenum (or water) to fall to the bottom of the plenum otherwise it would have to fight gravity to enter into the system as the air is being drawn into the system. This is also why the water drains are at the bottom of the filter housing. If the directional flow was from TOP to BOTTOM then the filters would get soaking wet every time it rained or you washed the car: ;)

 

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Seek to understand,^Value
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edjack said:
The air flows from top to bottom, and then into the car. Arrow points down. Ignore the writing.
QSilver7 said:
the air enters the microfilter compartment and flows UPWARD thru the filter
Hi Edjack & QSilver7,

We should iron this out because we can easily confuse others.

After having read the instructions that came with the filter, it was clear to me the air flow upward. But I could be wrong (as, in rare cases, the manuals and instructions aren't always correct).

Edjack clearly thinks otherwise - so please explain.

Bear in mind though that the leaves and debris are all found on the BOTTOM side of the filter.

But, I could be wrong as I only know what I read in the instructions, and what I see in my vehicle.

See also the
gunksny cabin air filter DIY (e39 Cabin Filter DIY.pdf) where I reproduce one of his pictures below:
- E39 Cabin Filter Replacement DIY


 

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Upon inspection of my car, the air definitely flows upward and into the cabin (car interior).

When I first bought the car and wasn't familiar with it, I had my indie do the major service. As part of that he installed new microfilters and installed them with the arrow down. It wasn't until later, when I began doing the replacement myself, that I realized the proper install is pointing up.

I suspect the filters work equally well installed either way, though :dunno:
 

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Merc Convert
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Discussion Starter · #8 ·
Or you could do as the previous owner of my car did and install 1 facing up and 1 facing down.
That's what I found when I removed them! I could see both upside down but who the hell would do one each way??! Especially since the 3M units have seats that are designed to install in the cabin filter housing.

So arrows pointing upwards? Despite the fact that the writing on the side of the filter would be upside down? I only stress this because I would think the writing would be oriented the way you'd place the filter into the box.
 

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Freude am Fahren
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Unless there is a prefilter, it is unimportant.

I get the ones with frames... Only one way to install.
 

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If one is using a microfilter that also has activated charcoal media...you'd want to insert them where the microfilter is removing pollen, dust, & dirt FIRST...then the air (now stripped of heavy particulates) should continue upward through the charcoal media. If you have the charcoal media on the bottom, the dirt/dust/pollen will fill the crevices of the charcoal...which hastens the efficacy of the activated charcoal...it is these natural crevices in the charcoal that attracts and holds on to the "molecules" of the "smelly stuff" (sorry I had to go simple...it's been a long day and the more scientific words are not springing to mind). :D
 

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insert them where the microfilter is removing pollen, dust, & dirt FIRST...then the air (now striped of heavy particulates) should continue upward through the charcoal media
Interesting intelligent observation!

I had never thought of that (having assumed that the charcoal was through and through).

Intelligent conversation such as that is why I like bimmerfest!
 

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Interesting intelligent observation!

I had never thought of that (having assumed that the charcoal was through and through).

Intelligent conversation such as that is why I like bimmerfest!
Well thanks, B'bee...now before someone questions my intelligence...could you add another "p" in the word striped in my quote.? :tsk: I mistyped the word "stripped". It's amazing how fresh eyes rereading what one wrote, can see the error jump off the page. :D
  • striped: marked with or having stripes (adj)
  • stripped: removed, torn or pulled off (verb)

Depending on which brand filter media you purchase...some may have a pollen filter on the bottom with a 2nd media above the 1st layer that "contains" activated charcoal (this is the media that looks "speckled). And some may have a solid layer of plain filtering media with a solid panel of activated charcoal. And you may also run across a cost cutting brand that may only have one media type that combines the activated charcoal media within the one layer of pollen filtering media. Personally, I would avoid the latter,
 

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Flat on top, ridges down. Also, the filter comes with tabs that fit under things at the right end and two upside down "U" shaped moldings that settle down onto the left side flange.

B
 
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