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  • ray80 12/15/09 6:55 am PST

    Is the problem the temperature of the output or the volume of output? If its the volume, does it change with fan speed setting (or can you at least hear a change)? Have you checked the cabin filters lately to see if they need changing? If its the temperature you ma want to ensure the coolant level is proper ( I:E: system was properly bled of air after t-stat change).

  • ab587 12/23/09 12:50 pm PST

    I have an 03 Rendezvous also and have been plagued with the same problem since the beginning. I'm convinced that this is largely a design problem as the airflow seems to have significant restricion when in heating mode (no rationale as to why). The thermostat can be an aggravating issue, but if you changed that recently you're probably eliminated a half or full open thermostat as the problem. (On cold mornings, does the temperature gauge get up to at least the first "quarter make" within a couple of minutes driving? If not, or it only goes above the quarter mark when stipped in traffic for a while, the thermostat could still be an issue.)
    That aside, I haven't the air filters to be the problem. In fact when I first started looking into the problem, I found that my Rencezvous had not had the air filters install from the factory! I've put new ones in with no noticeable change in air flow.
    It's possible that the air valve that changes with various settings is not moving completely into the correct postion when you change the setting (ie. panel vents, both, floor, deftost), but in general, I find that the blower just doesn't push much hot air unless it is set to the higher postions.
    Are you getting air flow changes when you change the settings?
    I don't have access to my service manual at the moment so I don't know how easy it is to look into the workings of the air flow valve. A dealer could tell you, but it's likely to be involved.

  • ray80 12/23/09 1:02 pm PST

    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

    Condition
    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.

    Correction
    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.

    Important
    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.



    7.-Remove the two screws that hold the mode door actuator mounting plate to the HVAC module. Remove the plate, exposing the mode door levers underneath. Refer to the illustration above for the location of the mode door levers.



    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.

  • Stever@Edmunds 01/14/11 7:52 pm PST

    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

    Condition
    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.

    Correction
    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.

    Important
    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.

    Source: 

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