Are you referring to the recirculation mode? When the recirculation button is pressed, an indicator light will come on. This mode keeps outside air from entering the vehicle. It can be used to reduce outside air and prevent odors from entering your vehicle. Recirculation may also help cool the air inside your vehicle more quickly once the temperature inside the vehicle is less than the outside temperature. The recirculation mode cannot be used with floor, defrost, or defogging modes. If you try to select recirculation in one of those modes, the indicator will flash three times and turn off. The air conditioning compressor will also come on when this mode is activated. While in recirculation mode the windows may fog when the weather is cold and damp. To clear the fog, select either the defog or defrost mode and increase the fan speed. Recirculation mode can be turned off by pressing the button again, or turning off the engine. This information can also be found on page 219 of your owner’s manual. If you have further questions, please feel free to contact me by private message. Thank you.
Tricia, GM Customer Service.