Buick riviera 1999 ユーザーズマニュアル

Use the FRONT button to quickly remove fog, frost or
ice from the windshield in extremely humid or 
cold conditions.

Select the FRONT button to defrost the windshield. By
choosing this button, the airflow will be directed at the
windshield. Adjust your comfort level by pressing the
TEMP up or down arrow. The fan speed will be
controlled by the system. You can change the fan speed
by pressing the top of the FAN button to increase speed,
and the bottom of the button to decrease speed.

The lines you see on 
the rear window warm 
the glass. Press the button 
to start warming your
window. An indicator light
in the button will glow
while the rear window
defogger is operating.

At speeds above 30 mph (48 km/h), the rear defogger
will stay on until you press the REAR defogger button
again. At speeds below 30 mph (48 km/h), the rear
window defogger will turn off automatically after about
10 minutes of use. If you press it again, the defogger
will operate for about five minutes only. You can also
turn the defogger off by turning off the ignition.