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2002 GMC Envoy XL HVAC Mode Door Issues

Discussion in 'Other Vehicles' started by George B, Nov 25, 2020.

  1. George B

    George B Full Access Member

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    Guys,
    I have been working to resolve an issue with the mode door on our 2002 GMC Envoy XL. I have replaced the actuator several times with mixed results but always ending up inoperable. I have not used a genuine GM part yet but the next one will be. I believe the part number is 89018539. Each time I replaced the part it would function for a short time and then default to blowing onto the floor only.

    I now have a Tech2 clone and will be working on trying to figure this out. I was messing with it this morning and can command the fan on and off as well as command the recirculate door to open or close but none of the other commands do anything and the control doesn't seem to want to go into calibration mode. In fact I can t determine which command is for the mode door as there is no actuator listed a such.

    Any experiences to share?

    I will try again soon and upload some photos or videos of what I am seeing.
     
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  2. TJ Baker

    TJ Baker Member

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    I have a 2002 Trailblazer 4.2 LT SWB with the automatic controls, RPO CJ2. Similar enough that if I select "Envoy XL" it still pulls up without error with the Tech 2.

    Looking at Body, Heating and Air Conditioning, special functions, Output Controls, Motor/Actuator Tests I see all 5 of my actuators although the wording is not consistent with other Tech 2 screens. Under data display the 'mode' actuator is called A/C Heater or something similar whereas in the special functions menu it is identified as "Mode 1 Door" . Similarly the Defrost actuator is called out as "Mode 2 Door". My 'recirculate' door is called out as "Air Inlet Door". All of my actuators can be commanded from here and I can watch the resultung 'counts' as the door opens or closes.

    Is this similar to what you are seeing or no?
     
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  3. George B

    George B Full Access Member

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    Thanks for the reply!!! I will check on this.
     
  4. George B

    George B Full Access Member

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    What happens when you try to command a recalibration?
     
  5. George B

    George B Full Access Member

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    Ran multiple tests on it tonight. All the actuators respond except for the one called “Mode Door 1” or “AC Heater” that one shows Demand/Actual of 0/1 for the counts. When I try to command it on it does not respond.

    When I command an actuator recalibration the HAVC control the screen goes blank and then returns to whatever setting it was on.

    I have a feeling the actuator is bad but I am unsure. I wonder if I can measure the command voltage at the actuator?
     
  6. George B

    George B Full Access Member

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    I also got a smattering of U codes.
    U1000
    U1026
    U1041 going to clean a ground for this one.
    1064
    1152 May be related to the rear ac. I have the blower module removed back there.
     
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  7. TJ Baker

    TJ Baker Member

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    Mine performs the recalibration OK
     
  8. TJ Baker

    TJ Baker Member

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    Well that one IS your mode actuator. I would need to test out mine tonsee if a low count is floor or dash. FWIW, none of my actuators go to 0. They more commonly 'bottom out' at a value somewhere in the teens.

    The Tech 2 sends a single command string to the HVAC module to initiate a recalibration. I don't think my screen blanked out for that, I believe it just ran the routine but I will check on that
     
  9. George B

    George B Full Access Member

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    I am going to order up a new one. I have taken this one apart and turned it manually by spinning the gears so it is likely messed up. I could always try to get the counts right I guess nothing to lose.
    Something like 110 counts.
     
  10. TJ Baker

    TJ Baker Member

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    Somewhere I have a document showing how to properly re-align these things. It involves getting the little wheel that is the encoder in proper alignment with the large final drive gear
     

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