upon initial start up our Acadia's hvac screen and all buttons are dark, but the fan still blows and the air will warm up after driving. After about 10-15 min the whole screen and all the buttons will flicker and then come on and stay on. Has anyone come across this in any gm vehicle that can help me out? Also I cannot switch from floor to any other position such as defrost, the rear climate control works fine while all this is happening.