My 2009 chevy 2500HD work truck is having an issue. Sometimes, when I'm sitting idling while doing paperwork on a job, after 5-10 minutes the ac will kick off. The system will change itself from recirculating to outside air, and the ac will show turned off. I can put it back on recirc but when I press the ac button the light flashes a few times. Then, after a minute or two, it will come back on for a few minutes, before doing the same thing again. I thought maybe it was because it's been so hot n it needs more airflow. So I installed an auxiliary fan with a switch. No change. Not low on Refrigerant. Ideas? This only happens sometimes. Happened twice yesterday and not at all saturday.