Ford 1999 Taurus Owner's Manual page 79

You can override the fan speed at any time. If you
use the thumbwheel to override the fan speed, the
EATC will continue to control the temperature but
you control the fan speed. To return to auto fan
control, press the AUTOMATIC button. If you are
operating in one of the override functions (FLOOR,
MAX A/C, etc.), automatic fan control will
continue unless you rotate the fan thumbwheel. To
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return to automatic fan control, press the
AUTOMATIC button. The EATC will return to
Automatic operation. If you want to return to any
override function, press the button for that function.
The fan speed will continue to be automatically
controlled.
Manual override buttons
Your EATC has six buttons which allow you to
make special selections. The buttons are located
along the bottom edge of the EATC control and
allow you to determine where the air will be
discharged. Pressing any override button changes
the air discharge location only. It does not affect
the ability of the system to control temperature or
the fan speed. Return to fully Automatic operation
by pushing the AUTOMATIC button.