I'm not sure where exactly is the Cabin Air Filter in my 2003 Voyager. Everybody look behind and underneath the glove box but no one knows where it's exactly located and how to replace it. Any ideas??

it will be behind the glove box .
Open the glove box push in on the sides and the glove box will come out the bottom hinge will hold it on behind that. There will be a plastic cover with 4 plastic tabs push them in pull the cover off and there is your Cabin Air filter.
there should be a diagram in your owners manual.
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Your cabin filter is located behind the glove box.
First you will need to remove the glove box. Open the glove box, and on the left and right side on the inside, there will be a retainer that you will need to pull out. This will cause your glove box to fall forward, exposing all of the screws. Unscrew the 10 screws around the outer edge of the glove box, and pull the unit down and out of your way.
After the glove box is removed, you will be able to see the HVAC casing. You will see the access door to the cabin filter, held in with some clips. Disconnect the resistor connector that is in your way, then remove the four clips in order to access the filters.
Once you pull the filters out, you can install the new ones in reverse order. Make sure that the arrows on the filters are pointing up, and that the door is sealed properly when you close it back up.
Good luck and please let me know if I may further assist you. -TXTEXAN

Your cabin filter is located behind your glove box. To remove your glove box, you will need to locate the two bolts underneath the glove box and remove them. Then open your glove box, and while holding your glove box, push inwards on the glove box stops on either side in order to allow the glove box to come out.
Once the glove box is out, you should be able to look in and see the slim access panel to your cabin filter. Just pinch the ends, and pull the panel out. Reverse for installation. Please let me know if I may further assist you, -TXTEXAN

If you are talking about the cabin air filter, this filters the outside air for the HVAC.
Hastings Filter (#AF1057) shows one for the 97-03 MY trucks.

Remove the screws that hold the horizontal filter housing cover from behind the glove box (no need to open the glove box);

Pull the cabin filter straight down (sits vertical behind the glove box inside the housing).

Install replacement and reattach the cover.

The cabin filter is located behind the glovebox.
First lower and remove the glovebox
If it has not been changed before, you will need to cut the plastic crossbrace behind the glovebox.
Once out of the way, unbolt the steel reinforcing frame behind the plastic and set it aside.
The cabin filter is mounted vertically behind it.
See images for further explanation:

u should be able to sqeeze the sides of the glove just far enough to get past the stops of the glove box. then u should see the access to the filter

behind the glove box

it is located behind the glove box. remove the screw holding the strut on the glove box. Squeeze sides of glovebox together to remove from dash. look into hole where the glove box was There is a removable panel for the air filter. take it out and pull out the filter. make sure you note which way the filter is oriented. push in new filter and replace cover and glove box.

Remove all of the contents in the glove box. Remove the glove box door support. Open the glove box. Squeeze the sides of the glove box inward, to drop the box door open further. The cabin air filter is in a small rectangular box, behind the glove box.

remove the glove box by pulling the sides in and opening it passed the stops. there's a 2" x 8"(approximate) box behind the glove box open the cover and you'll find the cabin air filter