2008 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 211

The recirculation mode cannot be used with floor, defog, or defrost modes. If recirculation is selected with one of those modes, the indicator light flashes three times and then turns off. The air conditioning compressor also comes 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. The recirculation mode can be turned off by pressing the outside air button, or by turning off the ignition. Air Conditioning #(Air Conditioning): Press this button to turn the air conditioning (A/C) compressor on and off. When air conditioning is selected, an indicator light comes on to show that the air conditioning has been activated. Pressing this button when the outside temperature is too cool for air conditioning makes the air conditioning indicator flash three times and then turn off to let you know the air conditioning mode is not available. If the air conditioning is on and the outside temperature drops below a temperature which is too cool for air conditioning to be effective, the air conditioning light turns off to show that the air conditioning mode has been canceled. On hot days, open the windows long enough to let hot inside air escape. This helps to reduce the time it takes for the vehicle to cool down. It also helps the system to operate more efficiently. The air conditioning system removes moisture from the air, so a small amount of water might drip underneath the vehicle while idling or after turning off the engine. This is normal. ;(Outside Air): Press this button to turn on the outside air mode. When this mode is selected, air from outside the vehicle circulates throughout the vehicle. An indicator light on the button comes on to show that it is activated. The outside air mode can be used with all modes, but it cannot be used with the recirculation mode. 3-33