From pg 282 of the owners manual:
A/C Air Filter
The filter access door is located under the instrument
panel on the passenger side. To replace the filter slide the
lock toward the rear of the vehicle (unlock position).
Remove the access door and pull the filter downward.
When installing a new filter, ensure its proper orientation.
Align the black arrow on the bottom of the filter
frame with the direction of airflow (away from the
blower motor and towards the center of the car).
If you don't have the owners manual and need one you can download it free at:
http://www.autousermanual.com/view/chrysler/pacifica/2004...