Recirculation Switch and Door Operation

[dmtaurus]

I researched the forum and didn't find the particular behavior that my LS, short wheel-base, 2006 Trailblazer, front-control only manual system, is doing.

A few days ago I noticed that the recirculation door would not operate (stuck in "fresh air" position) so I researched the forum and found the trick of removing the HVAC fuses in the fuse box located under the rear passenger seat and then running the engine with all the climate controls "off" for a few minutes. That fixed the operation of the door for a few days and it worked as it should when the switch was pressed on or off. Today I was testing the operation to make sure it was still working and the motor would not actuate the door. This time I removed the negative battery terminal for about 30 minutes to reset the system. When I restarted the system the door went to recirculation position and won't move in response to the switch setting. I don't know if it is the switch, the actuator motor, or something else that is the problem. It's sporadically working with feeding on/off battery power so it's not dead, yet. Any ideas as to what is causing the problem?

Also, I read that some people said the only way to get the actuator out was to remove the dash. But looking at the actuator location when the glove box is let down, it seems that if the speaker panel was removed from the top of the dash the actuator might be able to be taken out from the top. Would this be true?

 

[The_Roadie]

Sounds like a dead actuator. I've never had to change mine in that position, but it's only a couple hour project to remove the dash.

 

[dmtaurus]

I got to thinking about how the actuators actually operate. The HVAC controls are really servo controls for servo motors (the actuators). After that revelation I took the the HVAC control unit out of the dashand checked for the simple things like loose connectors or dirty contact pins in the plug. Using the wiring diagram out of a Haynes service book I removed the multi-pin connector from the HVAC control unit and checked for voltage from the recirc actuator. According to the diagram I should have been getting a voltage reading and the reading I got was about 11 volts. So before I would go to the work of removing the dash to try to get to the servo I'd like to be sure that it is the problem and not a problem with the control. Is there a quick test I can do with the plug removed from the back of the control that will actuate the actuator? Maybe with a wire jumper to ground? I'd like to test just the actuator without the HVAC control unit connected in the circuit.

From a quick parts check at Rock Auto I see that they sell must be selling a lot of control units, maybe as many as the actuators. And it would sure be easier to change the HVAC control than the recirc actuator.

 

[The_Roadie]

The actuator has two parts, the motor control and the position feedback potentiometer. Here is the wiring at the actuator end. The pot has a 5V reference input - pin 10, light blue/black. Ground reference is pin 7, yellow. The wiper of the pot is pin 9, light green, and can be anywhere from 0-5V depending on the position of the pot.

The motor control side has 12V on pin 5, brown. The control signal that you can fiddle with a jumper wire is on pin 6, tan. Ground it to spin the motor one way. Connect it to 12V to spin it the other way.

If you want to test this from the control head side, I assume the schematic you have contains the module connector pinout?

 

[dmtaurus]

From your citing of the pin numbers and the wire colors it would seem that you are describing how all the other actuators, except the recirc actuator, are wired and how they can be tested.

What I did was to go back and take the control unit back out of the dash and verify what wire colors and pins are there. Colors and wire numbers matched what I read in the HVAC 3 pdf file I downloaded from the manuals section of this site. I then followed the trouble-shooting steps for the recirc actuator as found in the same pdf. There are three wires to the actuator. From page 124 of the manual I grounded the dark green wire thru a 3 amp fuse holder. The door would not move. So from what I can determine the actuator or the wiring at the actuator plug-end are bad. That leaves me with how do I get the actuator out. From what your pictures show do you think if I just remove the dash that I can get to the actuator to remove it? I don't want to have to take the whole HVAC box out because that looks like I would have to disconnect the a/c and heater core lines.

As an aside I wondered if I cut a hole in the dash, beneath the snap-on panel that sits atop the dash close to the windshield, would I be able to access the actuator without removing the dash. I have a suspicion that the dealer techs may have a slick way to get it out without removing the dash.

Still, if I have to remove the dash then I will. I just want to be sure that if I do I will be able to get the actuator out without taking the whole HVAC box out.