I replaced the dirt & leaf encrusted filter with a new one but have absolutely no understanding of how this can work when it's exposed in the engine compartment. With the filter out, you can see the floor mat. There was evidence of mice in there as well so I put a screen over it in back of the battery. Can someone explain how the airflow can work when it's open on both sides?

 

There is a door that opens and closes depending on if you choose recirculate or fresh air. When you have the cabin filter cover on under the dash it is a sealed unit, and the air coming in from the cowl is being drawn through the filter into the blower motor.

 

So, if the battery cover is loose, air could come from the engine compartment? Where is the recirculate door? I'll have to look at it again....
I shined a light into the cowl towards the hole behind the battery and could only see a small gap for air to pass. An amazing piece of awkward engineering!

 

It has a flap that opens. Its the recirculate , then its closed. When you look down you should see the filter and the main door should be closed ( access door for filter ).

Video and filter here:

https://www.northamericanmotoring.co...er-filter.html



Diagrams:

Little plastic shroud cover that goes near that hole.


http://www.realoem.com/bmw/enUS/show...diagId=64_1162


http://www.realoem.com/bmw/enUS/show...diagId=64_1542