I've had my '07 for a few months now and on the handful of warmer days we've had (35-40ish degrees F) I'll start the car and sometimes find the A/C has engaged itself automatically. Is this by design? It doesn't happen all the time, but enough to pass the "fluke" threshold.

 

if you have the temp turned to max AC it will put AC on

 

If you did not turn off the a/c before you turned off the ignition, then yes, it will be on like the last time you used it.

 

So I'm guessing it isn't common! When this has happened, I generally have the temp dial maybe half way (straight up), the fan on speed 1, and the output directed to the floor. It never happens while the car is running - only when I first start it up, and it's never done it when its real cold - only when the temp hits around 32 or higher. I've tried leaving it on to see if it magically shuts off but seems to stay on.