Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

HVAC Mode Actuator door replacement

826212 Views 729 Replies 334 Participants Last post by  Ravalli Surfer
I just replaced my mode actuator due to the dash vents not working; it wasn't too bad of a job; you just need to be patient and smart as you work.

First you need to find out what part number to order; just call the local GM dealer. you will need to give them your VIN; the P/N I used was 89018675 and I got it from parts4chevys. $46.33 which was a lot cheaper than the dealership.

Remove lower dash covers. The actuator is located behind the middle portion of the dash; if you lay on the floor and look to the left you will see it.

Remove gray air duct as shown in pc #53; just pull it from its endpoint; this way you can get to the actuator better.

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.

Pic #46 shows the actuator; the two horizontal holes are where the screws mount; the other one close to the wire connection has a dowel that helps locate the actuator. You will need to adjust the white gear shown in pic #46
to be at the same location as the gear on the actuator you removed in order for it to go back in correctly. There are 3 marks on the back of the plastic housing (as seen in pic #46) and also slots in the metal part of the gear drive, the top slot is in the 1'oclock position in pic #46. Be sure your new actuator gear position matches the old and it will drop right in. I put the screws in the socket and then wrapped electrical tape around them so the screw wouldn't fall out during assembly. The whole thing took me 45 minutes.
The vents now work like a charm and I saved a bunch of coin!

You can doooo eeeet!


See less See more
721 - 730 of 730 Posts
Neon green is either Martian blood or a dye that's been injected into your AC Freon pressure circuit to find a leak. Obviously --- you've now found the leak.

I find it strange that the HVAC system didn't default to FULL DEFROST, as that's a NHTSA Federal rule for all autos made after somewhere around the change of last century --- assuring that, at the least, you can see out of the windshield even if you can't get warm or cooled.

The windshield was the airflow/defrost priority -- not human comfort.
Can I reposition door with actuator removed? I'm in South Florida, and gotta have A/C!
Thanks for the rapid responses! Very much appreciated!
I read a system code would be set if an actuator failed calibration, then thereafter that actuator would be disabled. If so, is there a way to check/reset the code without a Tech2 tool & laptop software?
I've added refrigerant a few times, some said they fixed leaks, and haven't seen the dye around the pressure switch recently. Is it possible the switch may be part of my problems? Will replacing it discharge the system? Sticker on air filter cover says 2.65 lbs (& dye) w/rear AC.
Anyone have detailed instructions/video on dash disassembly needed to remove driver's side actuators?
90°F+ typical here... need dash vents open! :(
That's a new one for me. I don't believe there will be any codes set for the actuators, good or bad..

I might be wrong, but my EXT needed 3 actuators and I never saw any SEL lit for that. All you'll get is a lot of clicking.

Freon leaks don't heal themselves. The only time they stop leaking is when all the freon escapes.

If you change that pressure sensor, you're gonna get a face full of refrigerant, refrigerant oil and refrigerant dye.

To confirm for yourself whether you have to pull the dash apart ... try go change that upper actuator first. If you have fingers like ET and can get it done ... so be it.

Don't count on that happenstance
See less See more
My mother-in-law had been experiencing clicking before her face vents quit working. My wife and I have an understanding in regards to working on her mothers 2002 Trailblazer. I fix anything that goes wrong with it and in exchange, I am allowed to live. =)

Her 2002 has the Auto feature. The part I purchased at a local Advanced Auto was Doorman 604-115. It is different from the original post in this thread as it does not have the attachment. Most everything has already been covered in this thread. I happened to have a 5.5mm and both screws were only hand tight. The discussion about the plastic gears being glued or pressed, I would agree this part is pressed on. In my case, the actuator case slipped right off, but without the piece still connected to the plastic shaft. I've not seen that addressed here before. You can see the cracks in the plastic casing showing why the piece slipped out. I thought that might be why the actuator was not turning so I plugged it back in and it was still dead. I ended up using the large nail puller below. I was able to get it under the lip about half way up on the metal shaft still stuck to the plastic shaft. I applied equal pressure with my fingers on the back side and was able to lift it straight off with a bit of force. If you look at the plastic shaft, you can see the results of the original actuator being pressed on.

On a side note, my MIL first took this to a local shop, as I had just done some other work for her and she didn't want to bother me again. They charged her $100 to diagnose the issue and then quoted her either $500 or $2000, depending on which part was the actual probably. Well, they knew what the problem was. They were just covering themselves in case they had to pull the dash after breaking the shaft. I paid $53 for the part and spent a couple of hours on the research/repair. Kudos to all who have contributed to this thread.

Hood Automotive tire Automotive design Bumper Material property

Hand Finger Household hardware Thumb Nail

Automotive tire Camera lens Finger Thumb Rim

Automotive tire Motor vehicle Automotive design Bumper Automotive exterior


See less See more
If you have the dual zone auto contgrols, there are actuators for the left and right side in addition to the mode and deforst actuator.
Greg, thanks for bringing that up. Was going to a few entries earlier, but decided. wait.

Not sure if the two slides for temp. are seperate or ganged together. If seperate,,, REPLCE BOTH! the hassell is not worth a second tear down. Again thanks!
Tnx Huggy and Ray et al

Yep. Wife killed the Battery with the four ways after taking a excursion off the road into a rock ledge and tearing up the right front suspension to the tune of $6500 during the blizzard 2 weeks ago.. A4WD :hopeless rather the 4HI was not the gear to be in with 3 inches of snow on packed base... She was fine. Body shop towing said by the time they recovered the TB the batt was almost dead.
OK... I figured a Battery soon. Got the TB back from the hospital yesterday and noticed the Mood (mode) :D function inop. Feet only.. "03" TB LTZ with dual auto magic A/C heat... Looked behind glove box and under dash and my mind glazed over. :crazy:

Huggy. Pictures Great help to locate the right stepper motor.
The question I have is has anyone figure out WHY the stepper motor/actuators grind their teeth just because the Batt went dead or got disconnected/replaced? One would think it would be like a reset or boot up like a fuse reset..
It concerns me because as I work on some things, I like to disconnect because of the chance of fissss wapping some electronics or smoking something and I would hate to have to replace several actuators every time I disconnect. Thats just crazy.
What raving miscreant engineer bane of mechanics overlooked this "little" anomaly.

Great site. Been signed up here as a lurker for some time and and find good stuff. Even for an old wrench like me.
Bear, ask Ravolli-surfer to send you his KAM battery change out or disconnect video!
This one will not disappoint: I started hearing that godforsaken clicking after hooking my battery back up from changing my injectors. Knew what it was, got the part, read around here to get an idea of the time I'd need and slated it for the weekend.
Before I continue, I just want to say that anyone doing this thing in under an hour or in less than 2 days, is either greatly exaggerating their wrenching skills or stands at a height of 18". Or both. Save your breath, I will not be swayed from this determination.
Anyway, I wound up pulling my seat out which made it exponentially more comfortable for an old fart like me, and I commenced to extracting this carefully nestled little device from its home. Sparing the reader all the gory details we can fast forward to the completion of my first install attempt. Something told me to keep my head under there for its maiden voyage. I didnt have the two gears meshed right and I could see it as soon as the key fell forward in the ignition. The 2 subsequent tries ended in the same maddening fashion so I braced up for a good hissy and pulled it off a forth time. In my sassy rage I disconnected both pedals and forced my head up there to see what fresh hell the gods at GM had wrought upon us mortals. All I could do was laugh entire paragraphs of curses at no one exactly because if I would have looked that far up there sooner, instead of doing it all by feel, I would have seen the 1" by 1/4" piece of tape that was crushed, accumulated and impacted in teeth of the black gear and saved my self a few hours of aggravation and borderline frostbite on my extremities.
I have no idea where it came from and I don't care at this point. I pulled it off, finished installing the new actuator
Ruler Office ruler Wood Rectangle Font
, fired up the truck and cranked the heat to 90.
See less See more
Horace, for future reference:

DO NOT DISCONNECT THE BATTERY - REMOVE THE APPROPRIATE FUSE(S). Why? Because when you reconnect the battery, the HVAC actuators inside of the dash are commanded to run a recalibration procedure which stresses the old brittle plastic gears inside the actuators and the brittle plastic gears break and leaves you unable to control where the air comes out, or control the temperature of the air, etc. Replacing at least one of them literally requires the removal of the entire dash! So, if you ever need to actually disconnect the battery, such as in the case of needing to install a new battery, be sure and use some kind of Keep Memory Alive (KAM) device to avoid the HVAC actuator recalibration routine.

You were "lucky" this time in that only one HVAC actuator went south. Depending on which HVAC system is installed there are either 3 or 4 other HVAc actuators and one of them is buried deep in the dash.

Good Luck!
See less See more
OK --- here's the KAM video --- as crude as it is ....

721 - 730 of 730 Posts