Hummer H2 2010 Owner's Manual page 184

Express-Open/Close Sunroof
The sunroof has a feature which allows the sunroof
panel to be opened or closed without continuously
pressing the switch. The express-open can be stopped
at any time by pushing the front of the switch a
second time.
The sunroof has four positions:
Comfort open stop: To open the sunroof and
sunshade, press the rear of the switch quickly and
release. The glass panel will open to an interim
position that reduces wind noise. For information
on using the sunshade, see Sunshade Operation
later.
Full open stop: To open the sunroof further, press
the rear of the switch quickly once more.
Express close: To close the sunroof, press the
front of the switch quickly and release.
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Vent: The vent position allows the rear of the
sunroof to be opened and tilted upward. With the
sunroof in the fully closed position, press and hold
the front of the switch until the sunroof reaches the
desired vent position or until it stops moving. To
close the sunroof from the vent position, press and
hold the rear of the switch until the sunroof is fully
closed.
Do not leave the sunroof open for long periods of time
as debris may collect in the tracks.
Dirt and debris may collect on the sunroof seal or in the
tracks that could cause an issue with sunroof operation,
noise or plug the water drainage system. Periodically
open the sunroof and remove any obstacles or loose
debris. Wipe the sunroof seal and roof sealing area
using a clean cloth, mild soap, and water. Do not
remove grease from sunroof.