In my experience with the engine auto on/off while using the AC, when the engine stops the AC fan keeps blowing the cool air though the compressor stops so the cool air will gradually warm up the longer you're stopped. Once it hits a certain temperature the engine turns back on and the AC blows as per normal. Not so much a problem when the car is sufficiently cooled down but certainly noticeable if you just started driving in a hot, stuffy car that's been parked in the sun. You can either turn the auto stop feature off or just lift your foot off the brake when the engine stops to fire the beast up again.