The expansion valve is behind the jack door compartment. You have to pull the rear passenger panel enough to remove the black plastic compartment. It is right behind there, brass in color with two lines in and two lines out. Torque the lines to 15ftlbs. when you reinstall.

I believe the black plastic jack compartment is held in with one plastic rivet near the top front.

To get to it,
1) Pull out the rear seat.
2) Unscrew the floor mounting plate for the rear passenger seat belt (large torx bit)
3) Remove passenger panel from the rear.
(At this point, you should only have to peel the large rear panel away by about a foot if you are willing to work in a tight space, otherwise, remove the whole side panel.)
4) Remove plastic rivet and jack compartment

Napa and Orielley both list the part as order in...unless you have an Napa warehouse nearby. Rockauto has the valve the cheapest.