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Thread: This weekend...All things ventilation distribution

  1. #1
    txtaz is offline Cadillac Owners Fanatic
    Automobile(s): 72,92,02 Eldorado
    Join Date
    Jan 2013

    This weekend...All things ventilation distribution

    My new to me 02 ETC has the typical problem with one side blowing hotter or colder than the other side. This is an indication of the air blend actuator not moving the blend door to the correct position.
    I also have the problem of the HVAC mositure cover (plastic/rubber piece on the firewall) is brittle and falling off whenever it's touched. By the FSM, this requires the motor to be lowered to replace. I have some ideas that may work to install and not lower the motor. Not sure, has anyone else replaced theirs and not lowered the motor? This will be the second project this weeknd if I can get to it.

    The first if the air distribution problem.
    I have read hundreds of posts, and they typically end with no resolution or one that is not satisfactory for me.
    So here that has a beginning, a middle and a satisfactory end (fingers crossed).

    My symptoms are the passenger side blows hot air all the time (yours could be cold, same situation) and there is a vacuum noise on the passenger side which sounds like air being let off every 5 or so seconds. The two symptoms are completely different problems.

    The easy one is vacuum. There are 4 vacuum actuators and colored vacuum lines for: park brake release, defrost, recirc and air up/down (which vents the air distributes to). My air distributes up and down fine, so I think one of the other actuators or lines has a small leak. A MityVac test on the vacuum distribution block will tell.
    Here is the diagram:


    Air blend actuators are a bit more in depth. There are 2 that all work the same way: passenger side, and drivers side. They are located behind the glove box with the passenger's side being on top and the driver's side being on the bottom. My passenger side blend door moves freely and the actuator moved jerkily when I changed the temperature to the extremes. I pulled the actuator and found the bull gear was cracked. Pictures coming soon (I'm charging the good camera).

    What didn't work was buying a Dorman actuator off Amazon ($65), slapping it in and "reprogramming" per the FSM. I might have goofed up and pulled the wrong fuse. The actual fuse is labeled comfort and is located in the trunk. I did reset everything on the actuator as I got it, re-installed and pulled the battery leads and shorted them out. Still no re-programming. I watch the actuator move (or not) while changing the temp to extremes.
    My plan is to test the door position feedback and the internal position potentiometer in the actuator. Next, I'll pull an idler gear from the actuator, measure the trigger voltage, and vary the door position and actuator position potentiometer to see if I can get the actuator drive motor to move reliably in both direction.
    Here is the schematic:


    Here is the operations for the air actuators.

    Attached Files

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  3. #2
    txtaz is offline Cadillac Owners Fanatic
    Automobile(s): 72,92,02 Eldorado
    Join Date
    Jan 2013

    Re: This weekend...All things ventillation distribution

    Here is the broken bull gear.


    I have tested out the circuit and found the door position signal is not getting the the actuator. Without feedback from the door position, the motor will run until something breaks. The bull gear has mechanical end stops so when the motor continues to run, it binds the gears. My bull gear split causing it to expand and bind in the case.


    To test the reference and door signals, first put a multi meter across pins 10 (+5v ref) and 7 (low V ref, NOTE this is not ground potential). Oh yeah, disconnect the actuator and test at the pins on the connector. This is the reference voltage, just turn the ignition on and it should read around 5V.

    At steady state, meaning the system is not trying to change the postions (which it can't since there is no load, you did remove the actuator connector), it will always read 5V. With a load (connected) this will flucatuate by the amount of power being used to operate the system.

    To test the door position feedback, connect accross pins 6 and 7 and start the car. Let it run for a few minutes. There is a warm start ciruit which determines what the HVAC controller should do and bypasses the door position feedback. With the car warmed up enough to actual give heat, manually cycle the blend door. Voltage should vary between pins 6 and 7.


    2.5 volts means do nothing, 0V means move in one direction and 5v means move in the other direction. Mine always wants to move. Not good.


    Mine does not, so I'm off to find the door postion sensor or whatever it is.
    Last edited by txtaz; 02-02-13 at 07:06 PM.

  4. #3
    txtaz is offline Cadillac Owners Fanatic
    Automobile(s): 72,92,02 Eldorado
    Join Date
    Jan 2013

    Re: This weekend...All things ventilation distribution

    The problem and solution....

    Problem....Dorman parts.

    Solution....AC Delco parts.

    My original potentiometer (in the actuator) that signals the door position had failed over time. I tried to save some money by going Amazon and a Dorman part. It turns out the parts did not match the OEM specs. I removed the idler gear in the actuator and turned the door feedback pot by hand to make the motor turn one way and then another. The problem was that the potentiometer was not stable enough to hold one resistance value. It kept jumping around on the meter and I could not get 2.5V constant. The motor kept switching directions.

    I got an EOM part from the dealer, slapped it in, pulled the plug to the controller to reset. Plugged it in an it reset itself like the FSM said it would.

    Everything works great now.

    There are a lot more details to what I did. I won't bore everyone. If you are curious, send me an IM.

    This is how you set the arm position on the actuator.

    Door Link Adjustment_resize.jpg
    Attached Images
    Last edited by txtaz; 02-02-13 at 07:16 PM.


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