Ford Explorer Sport Trac Owner's Manual page 84

Climate Controls
To manually turn off the heated windshield before the specified time has
passed, push the control switch again.
Note: Pushing the heated windshield button to activate the system will
increase engine idle speed when the engine is warm and is already at or
near its warmed up idle rpm. No increase in engine rpm will be noticed if
the engine is cold and running at higher rpms associated with cold starts.
This rpm increase is required to provide adequate power from the
alternator to the heated windshield and maintain power to the other
electrical functions in the vehicle.
84
2008 07+ Explorer Sport Trac (esp)
Owners Guide (post-2002-fmt)
USA (fus)