Congratulations! You're the 1,000,001th person to discover that the 4th gen auto climate control system is a complete clusterf**k. If you use the search function, I think you'll discover hours worth of reading of complaints on this disastrously designed system. I can only conclude that those who like the system have a preterhuman tolerance for abuse!
To mitigate (not eliminate) the bad behavior, I run my truck in non-auto mode all the time. This still enables auto temp control. The remaining infuriating foibles include the recirc function turning itself on anytime the cabin temp is above the outside air temp, which results in no fresh air intake to flush out the hot air, no matter whether or not the A/C is on.
You should be aware that the A/C compressor is engaged when you've selected defrost mode, although the "A/C" LED won't illuminate to let you know this. BTW, the "A/C" button only engages the A/C compressor and doesn't do anything else, far as I can tell.
To give Toyota their due, neither the '00 BMW 5-series nor the '05 M-B E320 CDI I've owned have had auto climate control systems which were that much better. But jeez, people, you're supposed to be engineers! You oughta at least understand that if the cabin temp is above the OAT, the last thing you want is the system operating in the recirc mode!!!! Dohhh!
Unfortunately, despite the huge number of complaints, Toyota has chosen not to address any of the problems of this sorry system during the life span of the 4th gen trucks (and I suspect the fix would have involved only a software rewrite/download, which is almost no-cost). Nor have they chosen to fix any of the other chronic complaints regarding lack of illumination of the overhead console or left armrest controls. To Toyota's credit (sorta) they finally put an expensive, albeit only moderately effective, fix on the rotten-egg-smell-exhaust complaints, but only after stonewalling their customers for two years, blaming the problem on 'bad fuel'.
Editorial comment: I've been a Toyota customer since 1969. As Toyota has grown and finally surpassed GM as the biggest auto manufacturer on the planet, their corporate posture has come more and more to resemble that of GM, which was the reason I stopped buying GM cars long ago. Could the fact that Toyota now pays their (non-unionized) employees more than GM, Ford or Chrysler pays have some bearing on this? I think that what goes around, comes around, and it's looking more and more like there is no Toyota 'management genius' capacity, as has been ballyhooed in the business magazines.