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Discussion Starter · #1 ·
I have 2004 Trailblazer and had the battery replaced two days ago. After I drove away from NTB my AC, which was working fine prior to battery replacement, will not blow out of front vents When AC "mode" is set to blow out front vents it will only blow at my feet and windsheild. Seems to be cooling well, except air no longer comes out front vents. The NTB people said that in GM cars the system sometimes needs to reset itself and it could take a few days or more and will work like it should when it resets. NTB said the dealership would tell me the same thing. What should I do?
 

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Yes. After battery replacement, the HVAC system needs to recalibrate all the mode, temp, and recirculate actuators. Those are little motors with feedback circuits, and they need to be undisturbed when they're in the middle of recalibrating. If you hit a control button or change the temp in the first 1-2 minutes after you start the car again, the calibration will silently fail, and it won't tell you except by blowing the wrong temp air where you don't want it. And more annoyingly - it won't even attempt the recalibration process again. It just gives up.

Simple fix. You can pull the battery off again for a few minutes, or easier: pull HVAC B fuse #36 in the rear fuse block (under the rear seat - driver's side) for 2 minutes. Then put it back in with the ignition off. Then turn the key to the RUN position, but don't start the engine. Don't touch the HVAC controls for 2 minutes, and you should hear the actuators and blower motor going through all the modes and speeds. Then it should be happy and you can drive away.
 

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Discussion Starter · #3 ·
Help again?!?!?!?

This did not fix the problem. Do you or anyone else know what else I can try?? Anything is a start!!
 

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Did the actuators go through their motions and make noises during the recalibration sequence? This is a very important question.

Your mode actuator could have died as a coincidence. The problem is definitely a failure of the mode actuator or the HVAC control box or the wiring between the two.

There are three actuators on the driver's side of the HVAC plenum behind the dashboard covers. The mode actuator is the middle one of the three. If you can disassemble your dash and look at it while it goes through a recalibration process, you can conclude whether or not it's dead. Want to be digging into your dash like that, or just pay a dealer to diagnose it for you? We can talk you through as much of this as you want, or as little.
 

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Discussion Starter · #5 ·
Help again!?!?!?!?

Yes it does make the noises and sound like it is going to work, however, I am not seeing ANY results.
 

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I'm having the same trouble with a 2006 Envoy XL. If you can teach me how to take the dash apart, I have already bought the new actuator.

Thanks for the help!
 

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actuators

Hello I have had the same problem with my 2004, The actuator that controlled the air for the vents stopped working after a little investigating and attempting the re-calibration process by pulling the fuse I found the actuator would attempt to reposition it self, long story short ended up being the encoder in the unit went bad replace the actuator and re-calibrated working fine now I will be glad to post pics of where the dash needs to be taken apart and where it is located, not all that easy of thing to do but better then paying the stealer,

BTW I got a brand new ACDelco actuator on ebay 25.00 look around there if you need one.

Jim
 

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If you do a search on here you will find all the info you need for changing out the mode door actuator including a how-to with pics.
 

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Discussion Starter · #9 ·
Front vents not blowing

Yes if you could show me where to take the dash apart and what to buy... I would be so grateful!!
 

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Actuator

Dustin Ill be glad to help you out Ill take some pictures of what needs to come out this after noon, as far as getting the Actuator you will have to do a search on ebay or online merchants, I found mine on ebay,
 

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Re-Dash,

Ok what you need to do is remove the knee bolster, just Below the steering column, first thing is to remove two 7mm blots that hold on the obd connector, then you will follow the black cover towards the steering wheel, Remove 2 more 7mm bolts Now care fully remove the black trim, Once that is removed you can now remove 4 7mm bolts that hold the knee bolster, two below the steering wheel one left and right side, and the other 2 are on the bottom of it towards the gas petal, with those removed it should make it easy to get to the actuator as shown in the pics on the other post, I fount the best ay to get to it was to lay on my back, mostly feel to remove it, when it stops raining I ll get out there and take some pics for you of the location for the dash bolts

Jim
 

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And between every bolt removed, remember to bellow at the required beer wench for a delivery. Take the bottle in your right hand, assuming you're right handed, tilt it smartly towards your lips, and enjoy. After four bolts and four beers, you may feel the need for a relief break. Using your right hand, assuming you're right handed .........
 

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Ha ha! Thanks for the help guys, but is that it? I had that panel off last time, and the actuator was in the center section of the dash, behind the radio and HVAC controls where I couldn't get to it. What's the trick? Going by the pictures I've seen I know that I'm looking at the right spot, but I can't see the actuator I need to replace because it's behind the dash panel still. Do I have to take the center console out?
 

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Dash panel

No you do not need to remove the center dash panel, all is done from drivers side, have to reach up there you can sorta see it but removing is done by feeling for the bolts on the actuator,

Just trying to help you out with it,

Jim,
 

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Alright, thanks guys. I'll have to give it another shot in the next couple days. Finals are kicking my a** right now, so this project is on hold for the moment. I'll let you know how it went. :tiphat
 

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Getting to Rear Fuses

Did the actuators go through their motions and make noises during the recalibration sequence? This is a very important question.

Your mode actuator could have died as a coincidence. The problem is definitely a failure of the mode actuator or the HVAC control box or the wiring between the two.

There are three actuators on the driver's side of the HVAC plenum behind the dashboard covers. The mode actuator is the middle one of the three. If you can disassemble your dash and look at it while it goes through a recalibration process, you can conclude whether or not it's dead. Want to be digging into your dash like that, or just pay a dealer to diagnose it for you? We can talk you through as much of this as you want, or as little.
Will I have to remove the seat to get to the rear fuses in my 2004 trailblazer? If you would tell me how to get to them I would appreciate that.:thx
 
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