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2004 Trailblazer_LT_ext and a 2005 Trailblazer LS ext
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8 Posts
Heat Blend Door Actuator & Rear Aux Actuator-correct parts?

I've read all the posts on this section, and just want to make sure I get the correct parts. I have a 2004 TB EXT LT with the digital climate control, and there are three issues:

1. It's winter now, and the front passenger side has plenty of heat, but the driver's side blows cold. All the modes work correctly for blowing air (dash, floor, and defrost), but we only get heat on right side (passenger), and no heat (cold) on left (driver). I think I have pinpointed that problem to the Blend door/temp actuator for the Drivers side, ACDELCO 1573598 {#89018676} (RockAuto has it for $34.99)

2. I also hear a clicking noise from the REAR passenger side of the vehicle (at the very back of the vehicle near the rear hatch). This was a noise I heard earlier, then is stopped, but when I went through the process of trying to reset the calibration (pull the fuse, don't touch controls for 90 seconds, etc and thank you all for those instructions) the clicking sound came back while recalibrating. I've pinpointed this to be the Rear Auxiliary actuator (probably missing gear teeth). I'm pretty sure this part is ACDELCO 1572811 {#88892975} RockAuto has this part for $46.79. (sorry, I can't post the links, since I haven't reached my 5 post limit yet)

3. Only unheated air comes from the roof vents. I THINK maybe that these are also controlled by the blend door actuator, but I'm not sure - or maybe the rear one - or is this another problem? Does anyone know?

I've been reading the threads on Trailvoy ever since we got our first TB (used in 2008), and you all are a FONT of knowledge. Because of the forums, we've been able to deduce (and fix) the problem with our A/C and stalling - to needing to clean the Throttle Body; we've been able to replace the Window arm regulator; diagnose and repair the shift arm controller; the upper ball joint, and more! I can't thank you all enough. I think I've only posted once, but read quite a bit. So, if anyone can chime in to verify the parts for 1 and 2, and have any information for 3, I would greatly appreciate it!

My husband and both work on the vehicle, but I do all the online research (he's mechanically savvy, but not computer savvy). He's got a code reader, if that will help diagnose the problem. We used to have a 2004 TB EXT LS (more basic model) but someone rear-ended us and it got totaled last year. Insurance covered a full replacement - same year, almost the same mileage (135,000), but a higher-end model with the digital climate control (LT). We do all the repairs ourselves, and keep it running smoothly. He likes the Chevy to work on much better than our old Ford, and this forum has been a God-send!
 

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2004 isuzu ascender
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8 Posts
Face/Floor Vent Actuator Replacement

I've read just about every thread on the subject of replacing the vent actuators, and I couldn't get my truck to divert air to the floor after installing the new actuator. :bonk: I have a 2004 Ascender, which is just a clone of the GM cousins: Trailblazer, Bravada, Envoy, etc. It also has analog controls.

The thing that has rarely been mentioned is that the vent door that controls air flow between face vents and floor vents "is spring loaded and defaults to the face vents." At least that's the case in my vehicle. When installing the replacement actuator, the white gear must be positioned so that the metal shaft slot is between the left most and center marks. This can be accomplished by plugging it in and turning the key to "on" and letting the actuator go through its full range of motion and turning the key off when it gets to the correct position. This may or may not be the position of the old actuator, so that's not necessarily the right frame of reference as most of the documented procedures indicate. One of the posts did suggest this position, but didn't explain why. You may have to tweak the exact position in order to get the gear to seat properly. After installation I let it recalibrate following the "pull fuse for 30 seconds, reinstall, turning ignition to on and letting actuators recalibrate for 90 seconds" procedure. Now works like intended!

It seems a lot of folks' experiences and write ups are based on pure trial and error. That wound up being my experience, but I was able to arrive at the solution by spending hours reading through most of the posts on this forum. I hope my solution makes it a little easier for the next victim of this failure.
 

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2006 chevy trailblazer_lt
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2 Posts
Need help 06 trailblazer lt.

I have the no air from the dash vents problems on my 06 lt trailblazer. Tore into it and could not figure out how to get the u shaped vent tube thats around the gas pedal out. Do i have to take the gas pedal off to get it out or do i need to try and move it out of my way enough to change the actuator?
 

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2006 chevy trailblazer_lt
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2 Posts
u shaped vent removal

the black plastic vent tube is held in place by a single plastic push pin. it can be removed by prying it, along with the vent tube away from the metal mounting bracket with a screwdriver, or narrow putty knife.
 

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2006 chevy trailblazer_lt
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2 Posts
what i learned replacing actuators on my 06 trailblazer

their are five electric servos that operate the a/c on g/m vehicles. the mode control servo controls the air flow out of the dash vents, and/or floor vents. the other servos control the air temp drivers side, air temp/passenger side, defrost vent, and re-circulation air/outside air (vent). if BOTH the drivers, and passenger sides wont switch air from floor to dash, or vice/versa, this is the mode servo. if you are not getting any air out of just one side, (driver or passenger), or only hot air out floor than you probably need the servo that controls heat for that particular side. the heat servo will cut out the dash vent when in "full heat" position. these servos fail because whenever the car looses electrical power (dead battery, or battery replacement) the servos must re-learn where fully open, and fully closed positions are. this is accomplished by them fully moving in both directions until they "stall out", because of their age, and being made from cheap plastic, this often results in one or more servos failing (by breaking their plastic internal gears, burning out the drive motor, and/or electronics). after replacing a bad battery in my trailblazer, the mode, and the drivers heat control servo had both failed. the mode servo is not hard to replace, but care must be taken to have the plastic gear properly align with the one in the heater box. the servo is located under the dash, on the drivers side, next to the center console. to gain access, you must remove a plastic cover covering the lower most portion of the dash (directly above the foot pedals) 4 small screws secure it. above that cover is a black plastic air duct that must be removed (the duct is held in place by 1 push-in retainer) after removal of duct, laying on your back, you can now see 3 of the 5 servos. the one most forward is for defrost, the one closest to the dash is heat control, (drivers side), and the middle one is the mode servo. to replace it: unplug the electrical pigtail from it, and remove the 2 screws securing it. when you remove the servo, the damper door it controls will fall to the "open" position. to make it stay in the half open/half closed (middle) position that matches the new servo you are putting in, you need to turn the blower motor on, and reach up to the plastic gear that mates with the servo, you can manually move it open, and closed with your finger by moving it back, and forth. as long as the fan is running, the air pressure will cause it to stay in the fully open, fully closed, or half position. when you get it to that half open/half closed sweet spot, you can screw the new servo in place. after installing, turn ignition off, remover fuse #36 (under passenger rear left seat fuse box), put pigtail wire back on new servo, re install fuse, turn ignition to "on" position, and allow all servos to re-learn their positions, (2 min.) DO NOT START THE CAR, or adjust any a/c controls during that time. if everything was done right, your vents should now work properly. if the mode select knob is non responsive, you probably have the mode actuator improperly installed, and the gears are not in proper alignment. the other servos just mount on a "D" shaped post, so no special positioning is required. the drivers heat side can be accessed after removing the above mentioned dash cover, and also the dash cover (at knee level), and the metal cover under it. 1 screw on servo was very tough to get to, i had to remove a additional metal bracket that goes between the plastic dash and the dash support, 2 nuts, and 2 bolts secure it. to remove, i had to the pry away the plastic dash just enough to snake the bracket out. i had read that the passenger side heat servo can be reached through the glove box hole, but that a portion of a metal bracket must be trimmed away to get to 1 of its mounting screws. this repair from the dealer could cost $300 to $800, so even if you spend a whole day fixing, you are way money ahead. i purchased my parts from amazon,
they were oem ac/delco, and range in price from $36 to $43 each including shipping, and i got them in 2 days. delco part numbers:
15-73596 mode actuator (controls dash vent/floor vent)
15-73597 passenger heat blend
15-73598 drivers heat blend OR windshield defrost (same part# for both)
15-73599 recirc air/outside air (vent)
 

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2004 gmc envoy_sle
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51 Posts
There are three actuators which one is which

Happy Sunday I have a 2004 GMC envoy my left side vent was blowing warm my right side vent was blowing cold I did a reset by taking the fuse out I put the fuse back in and now both vents arent working I'm in sunny Florida it was 96° yesterday with the index which of the Actuators Which one of them do I replace
Also what started all of this was my air Was blowing cold for 10 minutes 15 minutes then get warm
I would like some advice on which one to me please please
Richie
 

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2006 chevy trailblazer_ls
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1 Posts
After reading everything I could about this, I decided that this job should go to a dealer-caliber mechanic.....
I got the actuator from Rock Auto and my GM trained mechanic called to inform me that the new AC Delco actuator from RockAuto is defective and that I need the defrost actuator, as well......
 

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2005 gmc envoy_sle
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6 Posts
05 Envoy Passenger Temp Control

My 05 Envoy passenger side temp was stuck in heat, easy to get to.

Glove box has a open stop on a spring, just push it up and lower glove box.

Easy to get to I say! Not easy to remove, I had to cut away half moons of metal in order to get to the bolt behind the dash bracket.

After removing bolts, there was not enough room between the actuator and the bracket, so I put a flat strap around it and had my son pull it away from the actuator and whala! Same thing putting the new one in, have someone pull the bracket.

The cracked plastic was the cause of it not working, the metal center that connects to the damper door just spun.
 

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2003 chevy trailblazer_ls
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1 Posts
their are five electric servos that operate the a/c on g/m vehicles. the mode control servo controls the air flow out of the dash vents, and/or floor vents. the other servos control the air temp drivers side, air temp/passenger side, defrost vent, and re-circulation air/outside air (vent). if BOTH the drivers, and passenger sides wont switch air from floor to dash, or vice/versa, this is the mode servo. if you are not getting any air out of just one side, (driver or passenger), or only hot air out floor than you probably need the servo that controls heat for that particular side. the heat servo will cut out the dash vent when in "full heat" position. these servos fail because whenever the car looses electrical power (dead battery, or battery replacement) the servos must re-learn where fully open, and fully closed positions are. this is accomplished by them fully moving in both directions until they "stall out", because of their age, and being made from cheap plastic, this often results in one or more servos failing (by breaking their plastic internal gears, burning out the drive motor, and/or electronics). after replacing a bad battery in my trailblazer, the mode, and the drivers heat control servo had both failed. the mode servo is not hard to replace, but care must be taken to have the plastic gear properly align with the one in the heater box. the servo is located under the dash, on the drivers side, next to the center console. to gain access, you must remove a plastic cover covering the lower most portion of the dash (directly above the foot pedals) 4 small screws secure it. above that cover is a black plastic air duct that must be removed (the duct is held in place by 1 push-in retainer) after removal of duct, laying on your back, you can now see 3 of the 5 servos. the one most forward is for defrost, the one closest to the dash is heat control, (drivers side), and the middle one is the mode servo. to replace it: unplug the electrical pigtail from it, and remove the 2 screws securing it. when you remove the servo, the damper door it controls will fall to the "open" position. to make it stay in the half open/half closed (middle) position that matches the new servo you are putting in, you need to turn the blower motor on, and reach up to the plastic gear that mates with the servo, you can manually move it open, and closed with your finger by moving it back, and forth. as long as the fan is running, the air pressure will cause it to stay in the fully open, fully closed, or half position. when you get it to that half open/half closed sweet spot, you can screw the new servo in place. after installing, turn ignition off, remover fuse #36 (under passenger rear left seat fuse box), put pigtail wire back on new servo, re install fuse, turn ignition to "on" position, and allow all servos to re-learn their positions, (2 min.) DO NOT START THE CAR, or adjust any a/c controls during that time. if everything was done right, your vents should now work properly. if the mode select knob is non responsive, you probably have the mode actuator improperly installed, and the gears are not in proper alignment. the other servos just mount on a "D" shaped post, so no special positioning is required. the drivers heat side can be accessed after removing the above mentioned dash cover, and also the dash cover (at knee level), and the metal cover under it. 1 screw on servo was very tough to get to, i had to remove a additional metal bracket that goes between the plastic dash and the dash support, 2 nuts, and 2 bolts secure it. to remove, i had to the pry away the plastic dash just enough to snake the bracket out. i had read that the passenger side heat servo can be reached through the glove box hole, but that a portion of a metal bracket must be trimmed away to get to 1 of its mounting screws. this repair from the dealer could cost $300 to $800, so even if you spend a whole day fixing, you are way money ahead. i purchased my parts from amazon,
they were oem ac/delco, and range in price from $36 to $43 each including shipping, and i got them in 2 days. delco part numbers:
15-73596 mode actuator (controls dash vent/floor vent)
15-73597 passenger heat blend
15-73598 drivers heat blend OR windshield defrost (same part# for both)
15-73599 recirc air/outside air (vent)

I have AC that blows through all modes. The problem i am having is, when i turn the heat on, it only blows out of the windshield vent.
I replaced one of the actuators a year and a half ago. Dorman 604-111 Air Door Actuator
This was to fix the drivers side only receiving heat while the rest of the vehicle would cool.
 

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2007 chevy trailblazer_ls
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63 Posts
heat only from the defroster vents

Hello all. No matter what setting I have on the heater flow knob , I am only able to get heat out of the defroster (all the time, no matter what setting), and the dash vents. I can not get heat out to the floor setting vents. Any ideas to what is the problem would be appreciated. Thanks
 

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2007 chevy trailblazer_ls
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63 Posts
heat only from the defroster vents

I think the blower motor is fine. I get heat going through the defroster vents when the knob is set to floor only. For that mater, no matter where I set the knob, the flow goes always through the defroster, and never to the floor. Heat does comes through the dash vents also, but again ,never to the floor. Do you think the actuator 15-73596 is bad?
 

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2007 chevy trailblazer_ls
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63 Posts
Replace Defroster Actuator

Hello all once again. So I purchased the heater/vent flow door actuator, and in taking things apart, realized the actuator for the heater/vent was working, but not for the defroster. I removed it, and manually reached up and set the door to the half open/closed setting , same as the heater door. I purchased a new defroster actuator and my question is, when I reinstall both the defroster and heater actuators, do I set them as they are right out of the box, and do I leave the doors in the half open/closed position, reinstall the actuators, then do the recalibration procedure? Is this the proper way to reinstall them? Thanks to all the help.
 

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2004 chevy trailblazer_ls_ext
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6 Posts
Question about recalibration

Ok, so I do the recalibration (pull all the fuses, disconnect the battery, etc) and it works for 2-3 ignition cycles then loses the calibration again and I am right back to square one. is there something I am missing that locks the recalibration in, so to speak? :confused:
 

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2002 chevy trailblazer_ls
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3 Posts
I went to gmpartsdirect searched for the part number you listed. I have a 2002 TB LS 2.4L but it states its the wrong part. The diagram for the 2008 shows It as the middle actuator under driver dash. So it's the same part I need to replace. But It only lists it as a actuator GM no specific details. So I searched again but there's no same part coming up for my 2002 model. I then went to auto zone just to see what it gives me. They lists it as a Heat AC blend actuator. There's three for my base model for the main vents. One is this "Main Air distribution mode Actuator Only." This ones $138 so I assume its the wrong one. It has two others in the $40-50 range one is listed as the "Main. Air distribution mode. Cam and Actuator Assembly." The second is listed for the "Main. Air distribution mode. Actuator Only." The actuator only looks like the part you have pictured but doesn't show clearly the white gear coming out the side. I want to order the correct part online to get the best price but not to confident I can find the right one. I'm a novice a repairs so this will be a more advanced repair. So any help is greatly appreciated.
 

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2002 chevy trailblazer_ls
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3 Posts
I have a manual HVAC control panel. I just realized after searching again for the correct dash vent actuator part I have one other question. I saw this part "Recirculation Door Actuator; w/ Manual AC" for my 2002 TB LS. Since the recirculation air mode stopped engaging at the same time my dash vents stopped working I'm hoping the dash vent actuator is all I have to replace. Before when I have AC or heat on I push the recirculation button the light stays on when the dash vents stopped working I'd push it and now blinks a few timed then goes off. So is my assumption correct or does anyone know if these two functions require individual actuators? Also does anyone know where I can download the diagram of the entire in dash HVAC system. That would help determine where and if there a recirculation actuator for my 2002 TB LS. Plus help with future repairs. Thanks again.
 

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There's 2 actuators; you want the one with the white gear coming out the side; it's the lower one in pic #52. You will need a 5.5mm socket to get the 2 screws out; be careful not to drop the screws; take your time.
 

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2004 gmc envoy_slt_xl
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2004 GMC Envoy HVAC Mode Actuator door replacement

OK, here are my issues. 1)no air from dash vents 2)only warm air on driver side defrost with cold air coming from passenger side defrost 3)actuator clicking noise from passenger back/rear of vehicle upon recalibration but no changes. So my questions are how many actuators and where are all located (I'm under briefly and see 2 actuators but have not looked terribly closely) which actuators to replace. I can get 3 different ones on Amazon for under 100 for all. Each states it performs a different action.
"left main - temp", "main-mode" & "right main-temp" need help quick as not much hot air available from driver defrost. Thanks
 

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2004 gmc envoy_slt_xuv
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10 Posts
04 GMC Envoy XUV - Vents, Dampers, Actuators

I want to say THANK YOU to most of the comments in this thread. Very educational.
-----
I noticed shortly after replacing the batter (and yes following the hints described in several post) a few challenges
- AC would come on, but very little volume.
Solution: we cycled the modes and "wallah" everything was fine.

- But now, no air flow from the front vents at all, some from feet and dash, and rear seat vent works great (nice and cold plus strong fan).

Next step will be the fuse out option described and see if the bugger will play nice.
Again, Thanks for the info folks.
:thx
 

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Just bought an 02 Envoy at auction need help with warm driver air

Hey guys. Glad to have found a forum for Envoys. I'm active on several diesel engine sites.

Anyway I went to auction, picked up the vehicle I went after (a 99 chevy dually with 6.5L). My wife went with me and found a really clean 02 Envoy and we were able to pick that up as well.

Great day at the auction.

The passenger and rear air blow ice cold. Driver side seemed weaker air flow and was hot. We messed with the controls for a while and nothing changed.

From internet searches I see there is "reset" procedure where you pull the fuse for a few seconds..then let the system re-calibrate.

Then..how do I troubleshoot from there? If I'm counting right there are 5 or 6 different actuators in there.

Looking forward to using this site a bunch.

NH
 
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