Cabin filter replacement

[Fishboy]

After taking care to ensure the A/C was selected to recirc I successfully remove the filter cover and removed the existing filter which I'm assuming was genuine Lexus. It was fitted with the arrow facing up as directed. My replacement filter (crosland) doesn't have an up marking on it only the direction of air flow. I have fitted it with the air flow direction facing down as looking at the old filter this side was definitely the dirtiest, it needed changing. I was surprised how dirty the underside was on the old filter it must have been very restrictive. Is the direction of airflow from top to bottom? I just want to be sure.

Thanks in advance for your responses.

[johnatg]

The airflow through the filter is from top to bottom - ie the airflow arrow should be pointing downwards. The frame into which the filter fits has an 'up' arrow - that obviously should point upwards - ie opposite to the airflow arrows on the actual filter.

Actually I don't understand why the bottom side of the filter gets to look dirtiest (or at least blacker) - surely you would think that dirt would get trapped at the first surface it comes to and that (top) side would get to look dirtiest. But it doesn't!

This a subject of much debate on Toyota/Lexus forums worldwide, and just about everyone is confused! (And I'm not sure about me!)

And at the end of the day, I'm not sure what difference it makes - both sides of non-original filters look the same to me!

[Shahpor]

For what's it worth, this is what mine looked like when I changed it:

 

[Fishboy]

Gents, thank you for your responses. My filter wasn't as bad as the one in the photo but I think I have noticed an improvement in cabin airflow now I have replaced mine. Thinking logically about the airflow direction it has to be top to bottom otherwise if it was bottom to top any debris would drop down into the ducting.