Our software isn't reproducing Ray80's pics and is skewing the pages. I'm reposting the text here, so at least that will be readable.
If the flow seems restricted , this may help:
Minimal Air Flow In Vent Position With Full Heat (Disable Temperature Sub-Damper Door) - (Dec 9, 2003)
2002-2003 Buick Rendezvous
2001-2003 Chevrolet Venture
2001-2003 Oldsmobile Silhouette
2001-2003 Pontiac Aztek, Montana
with Front Manual (RPO C60) or Front Manual with Auxiliary Temperature Controls (RPO CJ3) HVAC Systems only
Some customers may comment on a lack of sufficient air flow from the instrument panel vents when the vent mode is selected and the temperature control is at full heat. Others may comment that the volume of hot air flow from the instrument panel vents may seem to be less than the air flow from the floor ducts.
Disable the temperature sub-damper door, located inside the air conditioning module, using the following procedure:
1-Turn the ignition key to the "ON" position and move the HVAC (heating, ventilation and air conditioning) temperature control to the full cold position.
2.-Turn the ignition key to the "OFF" position.
3.-Remove the instrument panel closeout/insulator panel.
4.-Remove the instrument panel compartment.
The mode door actuator described below may not be found on all vehicles. The actuator removal and replacement instructions are not necessary if this actuator is not present.
5.-Locate the mode door actuator on the passenger side of the HVAC module. Disconnect the actuator electrical connector.
6.-Remove the two actuator retaining screws and the mode door actuator.
8.-Locate the mode door lever, (1) in the illustration above. Remove the mode door lever by carefully lifting the lever locking tab and simultaneously prying outward at the base of the lever with a flat screwdriver. Be sure to pry as close as possible to the base of the shaft to prevent breakage of the lever.
9.-With the mode lever removed, swing the temperature sub-damper door lever (2) fully up. This opens the door fully on the inside of the HVAC module.
The sub-damper door may vibrate or fall closed if not secured in place. To ensure that this does not happen, use a plastic tie-strap to ensure that the door is held in place.
10.-Loop a tie strap through the channel of the lever. Loop the tie-strap over the upper actuator attachment boss, making sure to also get the strap over the side ribs, as the side ribs are the locating feature for the actuator backing plate. Refer to the illustration above for location of the tie strap.
11.-Install the actuator mounting plate on the HVAC module. Make sure the plate is seated against the ribs on the mounting boss.
12.-Install the mode door actuator onto the actuator mounting plate.
13.-Start the vehicle and check the operation of the HVAC system mode doors and temperature controls.
14.-Install the instrument panel compartment.
15.-Install the instrument panel insulator/closeout panel.
Ray's pics can be found here, here and here.