2004 GMC Envoy Owner's Manual - Page 151

Rear Climate Control System Your Envoy has one of the following rear climate control systems. With any of these systems, the rear climate controls will be disabled when the front climate control system is in defrost. This occurs to provide maximum airflow to clear the windshield. If your vehicle has the rear seat audio system, the lower buttons are used to adjust the rear seat climate controls. The temperature of the air coming through the rear outlets is determined by the front passenger's temperature setting. If the front climate control is on and not in defrost mode, the rear climate control can be enabled by pressing the lower power button (center button) on the control face. If the front is off or is in defrost mode, the rear climate control will flash "OFF" if the power button is pressed, indicating the function is unavailable at this point. The fan speed is controlled by the fan speed toggle button. The mode button, on the right, controls where the air is vented. The temperature of the air coming through the rear outlets is determined by the front passenger's temperature setting. Press the PWR button to turn the rear climate controls on and off. Use the mode knob to change the direction of airflow (upper, bi-level or floor) to the rear seat area. 3-31