I changed my cabin filter (recirc mode activated first!) and used an AC filter instead of the Denso OEM one. The AC filter has an arrow marked AIR instead of UP. Looking at the blower wheel, it is centrifugal, meaning the inlet is in the center pointing up. Therefore airflow is downward thru the filter into the blower wheel. This also makes sense since the filter should be the first thing in the system, to keep the blower wheel clean. So, the filter arrow marked AIR on the AC Delco filter should point down. I think this makes sense, but wanted to verify.

 

I did the same; but often I could smell stuff from outside I ordered another one (oem) and matched the arrow with the crate arrow. Not sure if it's right but no more smells from outside.

i an curious as well