Last year our 2008 H3 hummer started an a/c issue nobody can figure out. During the summer as you are driving and the a/c is blowing cold and hard, it suddenly goes to heater. If you turn the dials it will go back to cold a/c. We dealt with it, this summer same thing, driving and the a/c is working great then all the sudden, heater in your face. I have done the recalibrate but it didn't fix it. 2 mechanics cant figure it out since it doesnt do it while on the tester. Anyone know whats up?