Using this write-up by mach2plus, I changed out the cabin air filter & replaced the blower motor resistor in my 07 Coupe earlier today. I must say that the write-up really gave me all the 'heads-ups' I needed to perform this service. I only have a couple of things to add:

1) On my 07, the underdash cover behind the glove box is secured not with Phillips head screws but with Torx head screws. It takes a T20 to remove them. And you'll also need this for removing the resistor and/or the blower motor assembly. All of these mounting screws require the Torx T20.

2) There are actually 2 interlocks at the rear of the underdash cover. One is in the center just as reported by mach2plus. But I also found a second interlock on the RH side about 3/4 of the way back. You'll need to get both of these secured when you button everything up. I took a long, narrow blade screwdriver and pushed the plastics tabs on the underdash cover into the dash interlocks. Once this was done, I then pushed the underdash cover towards the firewall until I could reposition & secure the tabs on the front of the cover. Then you need to slightly pull the underdash cover towards the glove box until the openings for the two Torx screws are re-aligned.

Other than having to place my body into possibly 3 or 4 Kama Sutra positions (no comments!), everything went just as planned.

And was my blower motor & cabin filter full of stuff!!! No wonder my blower wouldn't run anymore. This is one design aspect of the car that should have been addressed instead of just following the M-B platform. As stated by others and specifically cautioned in the XFire Shop Manual, keeping debris out of the PS drain cavities is a must!!! Allowing debris (i.e., pollen, bits of leaves, whatever) to accumulate will result in water draining into the passenger footwell, which means it passed through the blower motor. You'll end up having to replace the cabin air filter prematurely and/or install a new blower motor resistor; possibly a new blower motor.

Later,