[BNaylor]

Welcome to AF.

Sometimes the ACC unit hangs up and loses reference or feedback to the temperature control actuators. Two - one for driver's side and one for passenger side. Turn ignition to on and then manually turn off the ACC and then ignition to off. Remove the battery negative cable for several hours. You may have to repeat this a few times. The GM dealers have a firmware update for the HVAC controller that is supposed to resolve this issue. If this doesn't work then check the fuses to the climate control unit and whether the temp actuators are responding when you vary the driver's and passenger temperature setting on the ACC unit.