ACDelcoGM Original Equipment 15-72811 Temperature Mode Valve Actuator Assembly , Black

Used this to fix the temperature control for the rear HVAC in a 2006 Envoy.If your Envoy/Trailblazer has a constant rhythmic clicking sound coming from the rear, for a few minutes after you turn the key on, then this is the item you need. There are two of these for the rear HVAC. Both are exactly the same part; one that controls the temperature blend door and one that controls where the airflow is directed. Inside this actuator is a motor, several gears, and a sensor. The reason for the clicking sound is because one or more teeth has broken off one of the internal gears. This generally happens when the HVAC system loses power such as when the battery dies or is disconnected, a fuse for the HVAC is pulled, when a wiring harness for the HVAC is disconnected, etc. In my case, I had to remove the center console in order to access the radio to replace a few burnt out lights. I had to disconnect two harnesses for the rear HVAC controls in order to do this. When power is restored the system needs to re-calibrate the actuators. It does this by having the actuator move the flapper in the HVAC unit all the way in one direction until it can't move anymore. It holds it in that position for a few seconds and the computer stores that position in memory (from the actuators internal position sensor). Then it rotates the other way and does the same thing. It needs these two positions in order to be calibrated. What tends to happen, is during the calibration process, while the actuator is holding the flapper in either the fully open or closed position, one or more teeth on one of the gears breaks off. Either the gears can't handle more than a few calibrations, or they just get a little brittle with age, I'm not sure. With a broken gear, the system can't complete the calibration and eventually quits trying (although it will try it every time you turn the key on) and you lose functionality of that particular actuator.The replacement procedure is fairly easy. You'll need to remove the interior rear panel. Mine had 5 screws toward the back of the panel and the rest was held in place by metal clips that disengage when the panel is pulled out. I'm not sure if this varies from year to year, or if the Trailblazer is different, so yours may vary. The HVAC unit and these actuators will now be visible. Now you need to locate which one is not working properly. The one on the side controls the temperature blend and the one on top controls where the air flow is directed. If you're unsure which one is clicking you can turn the key on and listen and feel each one. I do strongly recommend replacing both of them at the same time though since you already have everything apart. To remove the actuator you'll need to unplug the wiring harness and remove the three screws holding the actuator in place. At this point I have to say proceed with EXTREME CAUTION. The actuator more than likely will not just come off easily, and if too much force is used, it is easy to break the shaft that the actuator attaches to (I've heard of this happening several times). If it breaks in the wrong place you'll have big problems. Mine came off extremely hard. I used a screw driver to gently pry it out, and at the same time used another screwdriver to push on the shaft where it attaches to the actuator. The key here is to not use too much force and be patient. Once it's off you can install the new one. Mine didn't want to go back on easily despite everything being lined up properly. I ended up applying a light coating of grease to the shaft which allowed the actuator to slide on easily. Once your actuators are installed you'll need to calibrate them. First make sure your key is in the off position and all climate controls are turned off as well. Then, either disconnect the battery for a few minutes or pull the HVAC B fuse located in the fuse box under the seat behind the driver's seat for at least 10 seconds. Reconnect the battery or replace the fuse and turn the key on, you don't need to start it. That's it. Wait a few minutes and the system should be calibrated and ready to use. One note on replacing the interior panel; if you've never done this type of thing before, it is very important to make sure everything lines up properly before you start pushing it back into place. It's a good idea to remember the location of all the metal clips before you replace the panel. Then when you have the panel in place and are confident you have everything lined up properly, push on the locations where the clips are. It's easy to be off a little bit and have the clip or the plastic where the clip is attached to bend. If you can't hear and/or feel the clip locking into place as you push, then chances are that the clip bent.Hopefully this helps someone out. I replaced mine about a week ago so I can't comment on how durable it is. If it ever breaks I will update this review.UPDATE 1/16/2016It's been about a year and a half and this part has failed. Keep in mind that these things are really only stressed and generally break when power is lost to the HVAC unit such as when the battery is disconnected. Since installing I've disconnected the battery about 3 times and just today the battery died (it's -10 F). After installing a new battery the rear HVAC failed to work properly, and this part was found to be the culprit.So, this part works, just don't expect it to last more than a couple of battery disconnects/dead battery conditions.

These worked great for my 2006 Envoy Xl rear comfort controls. I actually bought 2 of these. One was for the head/floor blend door and the other was for hot/cold blend door. I recommend replacing both at the same time as I had one break and then the other a few months later. I made the mistake of buying a different set on amazon for cheaper but when they showed up they were set 180 degrees off and would not rotate enough to work on the vehicle. These mounted up with no issue and after following the recalibration process they were ready to work in about 20 min time ( total time for install and calibration.) calibration process was turn off all climate controls. Turn vechile off. Pull HVAC B fuse ( under rear (2nd row) driver side seat in fuse panel) then replace both actuators and plug them in then replace fuse and turn key to on but do not start vechile. You should hear/ see actuators turn all the way to one side and sit then turn all the way to the other and sit. After a few minutes they are ready to use. Start car and check complete operation.Wish I would have just bought these from the get go. Definitely easy to replace.

Clicking sound resolved by purchasing this actuator.... only go with AcDelco or GM for these, well actually any electrical part....

I have a 2005 Trailblazer that had the click-ity clicks in rear ac system on startup. I did have to replace my battery when this all started. I replaced both actuators since it was a bit of work getting back into the panel to fix this. There are a lot of guides and tips out there on how to install these so I will not get into that. BUT if you are changing the hot/cold actuator (the one on the side not the top) you WILL need a flat head screwdriver. The star stud that this installs onto has a slit it the tip because the shaft will have to be turned a little to get the star pattern to line up for the new part to slide on. This was a little tricky but as long as you don't use force and take your time you should have no issues. This is the one thing I didn't find in any of the guides or videos for this job.

Fixed my "Clicking" / vent problem. There's 2 of them back there and you'll only know if one is bad by taking it apart and looking for broken plastic gears inside. Metal gears would've lasted forever but would've cost GM 5 cents more! I changed both while I was there so hopefully I won't have to open up that part of the vehicle again for another 14 years.

I hot this to replace a failed Actuator and it has issues.It still causes clicking but turns off faster than my old one. The fan is super delayed. I have read that you may need to buy two or three to get one that is not defective.I can live with this as it is an improvement over my other one' but if you want something better buy the OEM' it's a little more. But less hassle.

This is the part used to stop the clicking sound you hear in the back of your trailblazer/envoy EXT with rear air. There are a few of these actuators, make sure you are replacing the correct one. Be careful getting the old one off, pry in a gentle circular motion. If you break the star gear on the flapper door you are hosed.After getting the old one off this one will slide on. Make sure you disconnect the battery. When you reconnect the battery, turn the key on without starting the vehicle and let it sit for at least 2 minutes. I just walked away for 10 minutes. This will calibrate all your actuators.

Don't waste your time on cheap knock off parts, these fit exactly as the should. No more clicking in the back of my ENVOY.

works great, just make sure you know how to calibrate the automobile when you install it or you can strip the gear inside again.