Blend Door (with pictures and the common problem)

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Electric Engineer
10-23-2011, 10:24 PM
The Blend door actuator is a motor driven positioner, a dc motor controls direction and the gearing to a potiemeter provides position feedback, to the climate control module.

To test the system if your blows just hot or just cold all the time, do the following.
If yours system blows cold.
1. start car, let engine warm up, turn on heat full, and Fan full on,
open fuse panel and remove "HVAC" fuse 10 a, fan stops.
Replace fuse, fan runs again and the temp of the air should go hot, if so that means the blend door is not stuck and the actuator moved, if the temp of the air goes cold in 10 to 12 seconds, the actuator is lost "no position feedback" and does not know the position of the actuator, the reason the actuator travels full hot and then cold, is because after power down and then power up it tries to find the home position but can't so it defaults to one of the full travel positons full closed "cold" or full open "hot".

2. Mine is cold so do the procedure above and when its blowing hot pull the ful again before it goes cold and remove the plug from the actuator motor before its commanded to close and go cold again.

Good Luck

11-15-2011, 08:13 AM
I have a 1998 Bravada with a blend door actuator problem. After following JBAG's post I found it very helpful. After looking over the issue I would like to add the following. I found no need to disconnect the vacume line as to avoid snapping it like the previous poster. With the vehicle running I moved the position selector to determin what position would leave the vacume arm with the least tension before "gently" prying the vacume pump up and off. For my vehicle it was in the vent position. With out the arm having tension on it the vacume pump will come off easier. Once the pump was pried off (up). I again moved the position selector and found the position that extended the vac. pump arm the farthest. This allowed it to flex easier when moving it forward out of the way over the plastic mount tabs. My suggstion for removing the two actuator screws is that don't rule out using a 7/32 open and box end mini wrench. I also would recomend a 1/4 drive with a "flex head" or 1/4" stubby. Hope this helps and again thankyou JBAG for pointing me in the right direction.

11-15-2011, 08:19 AM
Follow up to my previous post. Make sure you again move the position selector to your previously determined slack postion when reinstalling the vacume pump and then follow the instructions for recalibration.


11-26-2011, 11:39 AM
Thanks for the posts that put me on the right track with a blend door actuator problem on a 1998 Olds Bravada. Now that I have done it I have several improvenents on doing this job. Look to previous posts for location and access to the BDA. As previously stated you will need a 7/32 1/4 drive and I would also have a 7/32 mini wrench open and closed end available. First I did not disconnect the vacume line to the vacume pump so as to not risk breaking the mini inlet nozzle, hose or fitting.. there is enough hose to work with when removing and swinging pump out of the way. Then I found that I needed to start the car, and find the right position on the air direction control knob so that there would be NO tension on the vacume control arm before gently prying up the the vacume pump to get it out of the way and have access to the blend door actuator in my case a (Dorman #604-106 for an auto climate control application). On my Bravada putting the direction control to "vent" relieved tension on the vac pump via control arm. Turn engine off. Once the vacume pump is pried up/off I again started the car and changed the direction flow knob once again as to give me the max arm extension off the vac pump arm. Why? so with the arm on the vac pump extended it would flex easier when having to swing the Vac pump over it's original tab mount swinging it toward you and to the left out of the way. Work slowly and methidically as to not break the tab at the end of the vac pump arm attached to the direction flow flap. This means the vac pump will remain connected to the direction flow door tab. Don't use a 1/4" straight ratchet drive but use a 1/4" "flex head" drive ratchet. There will come a point where the ratchet will not ratchet any more. You can then use the the 7/32 mini wrench or if having small hands, like me, was able to put the socket alone on the first of two screws that need to be removed and removed them the rest of the way by hand. Having a handle magnet available to retrieve the screw if you drop it is advised. Ok once the two front screws are removed, gently pry up the actuator to remove. Check pin configuration on your old actuator and your new actuator. "I believe" the auto units are 5 pin and the non-auto are 4 pins. OK now with the actuator removed feel your way up to the blend door stem and turn it open and closed to make sure it turns freely. Make sure your car is turned off and NEVER put any power to the new BDA before total installation and tightening. Pay attention to the location of the keying on the new BDA and the location of the keying on the BD itself. It will be a neutral position. Look at the BDA and then aligning the BD itself to a similar position as best you can. A little playing with the alignment will be necessary. You know you got it right when the BDA drops dn on the screw hole mounts. After the 2 screws are tightened you can connect the wiring plug to the BDA. Now gently slide the vac pump up, over and forward to get it in postion to remount. STOP, now start car and return direction flow knob to the original no tension postion, on my (98 Bravada) the "vent" position. Stop car and then remount vac pump. You should be good to go. On inspecting my old BDA, as previously found by others, discovered the main drive gear cracked.

Good Luck,

02-08-2012, 10:11 PM
I have a 97 Bravada with same symptoms as some on this thread. Heater core is shot and actuator is broke. I have the new heater core ready to go in and a replacement actuator. According to GM and every other parts house, I have the correct replacement actuator. (the part number has changed from 16124922 to 89018356)
Now here comes the tricky part. The old actuator has six pins numbered right to left 5 to 10. So does the new part. The old part used pins 5, 7, 8 & 10. The new part has pins 5 & 6 removed. Does anyone know how I should rewire the plug so the correct wires are in the right spot? The control on the dash is a simple red/blue temp knob.
Thanks for any advice.

02-13-2012, 07:46 AM
I personally would not be trying to re-wire the blend door wiring harness. The pin configuration should be based on whether you have a manual or automatic heater controls. Look for Dorman to save money, probably half of a GM price. The BDA for auto climate control will be much more then the BDA for a manual contol set up. I don't remember seeing manual controls on a Bravadas but that is mostly in 1998-2001.

02-13-2012, 08:14 AM
Read nightskyrider's thread again and have a question. What is shot about your heater core? Is it leaking or plugged. when I got my 1998 Bravada it had no heat. There was two reasons for me. Blend door actuator and plugged heater core. Literally took ten minutes to unplug heater core. With Bravada at operating temp., feel both hoses going to heater core. If one is hot and the other is not then there is no flow through core. I slid the hoses off and connected a garden hose and back flushed it. Cleared right up. Might even consider runnning some radiator clean chemicals in the core and let it set. I then carefully cleared the water out with my air compressor. When the core is dry I added via funnel fresh Dex cool until it ran out other side and then put hoses back on. The problem with most of these 4.3s using the red dex cool is two fold. First anytime you have one of these you need to replace the rad. cap with a Slant 10230 or a Slant 11230. Second fill your resevoir to the "hot" level when "cold" The Dex-cool gels and clogs form contaminates and air infiltration

06-12-2012, 08:00 AM
I have removed my Blend Door Actuator and noticed that the shaft that it sits on turns freely with the car off, once the car is on the shaft does turn one way but unable to turn it back to the other position, unit I turn the car off. Is this normal, I don't want to buy a Blend Door Actuator and install it and have it break the gear again.

Also the VAC thing in front of the Blend Door Actuator has broke of the little plastic thing that the arm connects to, could this be why the shaft does't spin freely?

06-12-2012, 08:25 AM
Unfortunately I cannot answer either of your questions. Don't remember when I did the BDA replacement about the shaft it sits on. The only thing I can think of is if heater motor is activated and putting pressure on the shaft/door or is the vacume arm controlling the shaft you are referring to? If so then I would think this is normal. Did you break off the vacume hose? I tried to caution when working with the vac arm removal.

06-12-2012, 08:34 AM
I broke the piece that the metal part of the vacuum arm connects too, is that piece replaceable?

And would it be a problem if i remove the DBA, and just turn the shaft to Cold for the summer and back the other way for the Winter, its a cheap fix for now.

07-16-2012, 02:41 PM
My blender door wasnt working (hot air only when a/c turned on). looked behind glove box and you can see the actuator motor behind the vacuum for the flapper door for defrost/heater/vent. easy to get to with a 1/4 ratchet and 7/32 socket. replaced mine with a surplus part. 10 bucks!!

06-10-2013, 01:30 PM
My comment goes way back to the start with input by riccbhard of June 4, 2006, and a later comment by another concerning a quick fix for the split gear that causes the problem. Photo by riccbhard shows the separation in the larger plastic gear that is the common problem. The other viewer advises to simply put the damaged gear back on so that the split never comes into contact with the blue programmed gear. My input here is similar, but with a variation. The gear inside diameter is simply too tight, and with normal plastic deterioration, it becomes brittle and cracks. Reversing the gear is something that I've used on other projects, and it does work because it stresses to push the split back together. This gear has a recess about 1/4 in. wide and almost as deep. I used a length of stainless steel wire, fine, and inserted it into the recess, then used hot glue to secure it to the bottom of the recess and against the center hub. Continued this all around the gear, until lastly, using needle nose pliers, I twist the two ends of the wires together to tighten them. Finger pressure to compress the split aides in the twist. Then snip off the ends, bend the twist back into the recess, and hot glue all around -- wet to cool. Don't do the bottom side because there is a platform component that fits into the recess from below. Adjust the gear so that the split area does not come into contact with the blue control gear, the further away the better. Slide the gear back on, but you'll note that the split reappears, but smaller, but it now has additional structural support of maybe block future failures. The good news is that the center gear teeth are still engaged, but the stress is less, so it may last for years. Mine works perfectly. Lastly, others in other places, indicate that all the gears must fit exactly as they were when removed -- not true! All the gears, except for the blue program control gears are simply speed gears that translate high speed off the electric motor to slow speed gears that the blue program gear uses for timing and collective sequencing of the blend doors. You cannot put the actuator back together wrong, so long as you have the stop-ear within the stop recess. Lastly if the console vents are wide open, connect the plug to the disconnected actuator, and manipulate the vent control until the stop is fully to the right as you look at the stop, if closed, then it is fully to the left. Reinstall, and enjoy a virtual no-cost solution.

11-07-2013, 07:47 PM
This is my first time at this and don't know if this is the right forum or not but here goes.

I have a 1998 Chevy S10, LS, 2 wheel drive, 4 cyl., manual heating controls in which I can only get lukewarm air out of.

In the past when I had this problem, if I hit a bump hard enough it would cause the heat to work OK if I had it set to that setting with the temperature control and vise versa for cold air in AC mode.

I have read several posts/threads concerning the blend door actuator and those gave me an idea of what to look for.

I picked up a blend door actuator at O'Reilly's and figured I would start looking for it.

I dropped the glove compartment interior and all I could find was a sphere with a vaccum line to it. When I looked up the actuator on O'Reilly's website it said it was on the driver's side. This particular actuator has four pins for the connector.

I've had the radio out, heating/cooling panel out, dash parts under steering column out and cannot see anything similar to the actuator that I purchased.

I called the local Chevy dealer and the parts department said that the temperature control actuator is located on top of the heater case. Where is that???!!! and how do you get to it on my particular type of S10?

11-08-2013, 10:39 PM
Update to my Nov 7th post:

I did find the blend door actuator behind the glove compartment on my 98 Chevy S10, LS, 4cyl., 2WD with manual heat.

It was located exactly where the photos on page one of this forum said it was but was hidden by the vacuum control. You have to definitely remove the vacuum unit in order to see it.

One idea that I ended up using was to place two pieces of computer paper, stapled together at the top, on the right side of the vacuum mount and made sure it went all the way to the back to make a trough. That was a saver as it caught the right screw when I dropped it trying to put it back in.

I was only able to get a 7/32" ignition wrench on the screws and I could only get a 1/8 to 1/4 turn on the nut head each time.

So as far as the 98 S10 goes you don't have to take the dash completely off in order to replace the actuator unless you have the hands the size of meat hooks. I have small hand but ended up with five bandages on them trying to get the screws back in.

Boy do I have HEAT!!!

Thanks for all the advice on this page as well as the previous 4 pages of information.

08-06-2014, 10:57 AM
Just did this repair on a 2000 Blazer with automatic temp control. I bought the Dorman 604-106 part. It is made differently than my broken one.

I strongly suspect that the gear from the cheaper manual actuator could be swapped into the automatic controller that has a broken gear. The Dorman parts are designed differently, but I've been in both of them and if you get the $144 Dorman part and it then breaks, you can buy the $44 manual one and swap the gears. You could likely do the same with the two different GM parts.

PRO TIP: Wear mechanic's gloves and use a thumbwheel ratchet!

I found a 1/4" Thumbwheel ratchet from Harbor Freight to be worth its weight in gold for this project. It was very easy to remove and reinstall the bolts that hold the actuator. It fit in the area just fine and I was able to turn it easily.

10-23-2014, 05:28 AM
I had heater issues...tried changing accuator (thumb wheel extension on 7/32 socket made removal a snap...) ended up being clogged heater core spent $140 to find out it was a 5 minute fix and free also! Make sure heater core is not clogged before changing accuator

07-12-2016, 02:16 PM
On my 97 Blazer everything in the a/c system is new, even the blend door motor and I still have the same issue. When it's overcast and the sun isn't beating down nasty hard, I get pretty cold air out the dash but not spectacular. But when it's blazing hot, it's barely a whisper of medium cold. If that's a measurement. Is there a certain timing for the blend door motor gear that I didn't get line up correctly? With 38 on the low side and 185 on the high side and the accumulator will freeze your hand, what's the problem, does anyone know?


07-12-2016, 03:18 PM
If it's 90 outside, 140 inside what do you think the ducts are? Sunshade cover. Step daughter complained that her a/c wasn't blowing cold enough. She never put the sunshade in place. Next time she stopped by. I put the sunshade up, waited around 4 hrs and drove it around. Pretty cold. Get a meat thermo and see what actual temp is blowing out the vents.

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