e-man

Just curious, how can you tell if it's working? If it's broken, does it make all kinds of weird noises?

L8Apex

I assume the arrow on the filter should match the direction of the arrow on the filter housing. But the instructions taht came with my carbon filter tells me to point the arrow down. I noticed this filter also fits the Camry. Then I thought maybe the filter housing was simply stating the housing side up.

Boron

If the panel filter manufacturer is using the arrow to indicate which side is down (airflow being up) then that's how it should be installed.
If the arrow is indicating airflow direction, then match with the holder's.

I believe the carbon side is the one facing the incoming air, rather than exiting, but it could also be a case of the arrows printed for another vehicle's holder, where the edge pleats are used to anchor it in place, which the 3GS doesn't.
Best to ascertain from the manufacturer what the arrow is indicating - airflow or side facing the incoming air.

L8Apex

Will do Boron. The manual says to match the arrow of the filter with the holder. When you put it all in. All arrows are facing up. I went with that from now. Will call in the AM.