Well, here is the good and bad news.... Had the same issue, same approx. mileage, same year... The unit seems locked up. Air comes out, but one speed and auto or manual has no effect. Bet you that when you press the A/C button the A/C indicator lamp will blink....
Good News... The computer is contained in the climate control unit itself, not part of a remote module.
Bad News... You will need to replace the control module. Mine had a bumper to bumper warranty still in effect, so covered.
The part is 55111955AC, List price $132.00 plus a core charge... on parts sites I use, one was at $92.20 plus core charge, the other $105.60 plus core charge. So not that huge of an expense but still not one you should have at 40K miles.....
I didn't do mine but see it as a super easy DIY. Remove the center stack trim. Unbolt the control unit and unplug. Plug in the new one.