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post #1 of (permalink) Old 06-07-2017, 04:47 PM Thread Starter
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blend door actuator failure

I have my share of this problem. Does anyone know exactly what's happening? Why the ticking noise? I replaced 2 of mine. And just replaced one of the two for the second time. I am really curious what happens. Do gears get stripped? What I just replaced appears fine. Or is it the motor too powerful for the plastic gear that the gear is pushed beyond?

Last edited by paker; 06-08-2017 at 07:24 AM.
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post #2 of (permalink) Old 06-07-2017, 05:23 PM
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My understanding is that the teeth on the main plastic gear break... What brand are you using when you replace them? Another poster recently said that he purchased a Dorman replacement from AutoZone and it had a lifetime warranty.

Are you saying that the one you just replaced was taken apart and you didn't find any gear-related issues and it was still clicking?

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post #3 of (permalink) Old 06-07-2017, 09:41 PM Thread Starter
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........Are you saying that the one you just replaced was taken apart and you didn't find any gear-related issues and it was still clicking?

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True. It is ticking but all gears are intact. This one is on the right side of glove box. It opens/closes the heater door.
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post #4 of (permalink) Old 06-08-2017, 12:07 AM
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There are several of them under the dash at various places; could it be that a different one has broken, and not the one that appears to be unbroken?
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post #5 of (permalink) Old 06-08-2017, 05:17 AM
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If none of the gears are damaged at all, then it makes no sense that it would be clicking like that... My understanding is that the issue is always related to broken teeth on the main gear...

Can you post a close-up picture of the inside of the actuator? I''m curious to see what it looks like inside if it's clicking without any broken teeth...

Does anyone else know why it would click if its not a a gear problem?

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post #6 of (permalink) Old 06-08-2017, 05:43 PM Thread Starter
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Here are the gears. They are intact. No tooth is missing. I put my finger on the ticking actuator to find the faulty one. No way I took out a good one.

Yes, this is Dorman I bought from Amazon for Prime delivery. I doubt Amazon offers lifetime warranty.

My best guess is that the motor has too much torque for this application, making gears skip. DC resistance is 37 ohms. If I hear ticking again, I will add a small resistor inline to cut down current draw to less than 100 mA.
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post #7 of (permalink) Old 06-08-2017, 07:07 PM
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Here are the gears. They are intact. No tooth is missing. I put my finger on the ticking actuator to find the faulty one. No way I took out a good one.

Yes, this is Dorman I bought from Amazon for Prime delivery. I doubt Amazon offers lifetime warranty.

My best guess is that the motor has too much torque for this application, making gears skip. DC resistance is 37 ohms. If I hear ticking again, I will add a small resistor inline to cut down current draw to less than 100 mA.

the problem lies in the way the hvac computer works in these cars, there SHOULD be a part within these actuators that can "see" where the door is stop to stop on each end, but there is not, in stead, it relies on current draw of the motor. it sees the current go high and "knows" that the door has reached an end position. the way I am attempting to preserve the motors in my car is to not run the temp all the way to an extreme, if you go just two clicks before full cold or hot it won't look for the full stop and try to shove the door to reach the high current "stop"
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post #8 of (permalink) Old 06-08-2017, 08:27 PM
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Replaced my blend motor in 2015, no issues but I used AC Delco. Personally I'm not a dorman fan.
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post #9 of (permalink) Old 06-09-2017, 12:19 AM
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Originally Posted by IMSITTINGINYOURCHAIR View Post
the problem lies in the way the hvac computer works in these cars, there SHOULD be a part within these actuators that can "see" where the door is stop to stop on each end, but there is not, in stead, it relies on current draw of the motor. it sees the current go high and "knows" that the door has reached an end position. the way I am attempting to preserve the motors in my car is to not run the temp all the way to an extreme, if you go just two clicks before full cold or hot it won't look for the full stop and try to shove the door to reach the high current "stop"
I've been using one click from full stop each way.
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post #10 of (permalink) Old 06-09-2017, 05:02 AM Thread Starter
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Originally Posted by IMSITTINGINYOURCHAIR View Post
the problem lies in the way the hvac computer works in these cars, there SHOULD be a part within these actuators that can "see" where the door is stop to stop on each end, but there is not, in stead, it relies on current draw of the motor. it sees the current go high and "knows" that the door has reached an end position. the way I am attempting to preserve the motors in my car is to not run the temp all the way to an extreme, if you go just two clicks before full cold or hot it won't look for the full stop and try to shove the door to reach the high current "stop"
This is interesting. I was wondering about end point detection because the motor has only 2 wires. If I add inline resistor to cut down motor torque, the hvac brain may not see high enough current.

A related question. How is temperature selection knob position related to blender door hinge position? Are there position sensors on the doors? I have seen some actuators with built-in position sensor, but ours have just 2 wires.

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post #11 of (permalink) Old 06-09-2017, 05:37 AM Thread Starter
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Replaced my blend motor in 2015, no issues but I used AC Delco. Personally I'm not a dorman fan.
I think AC Delco is the OEM actuator that goes bad in our Impalas. I purposefully chose a non-AC Delco brand.
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post #12 of (permalink) Old 06-09-2017, 08:38 AM
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On some old Fords with hvac horizontal slide bar controls, I put a dab of clear silicone at the ends of each slot to prevent full travel, lol.
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post #13 of (permalink) Old 06-09-2017, 01:03 PM
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Quote:
Originally Posted by paker View Post
This is interesting. I was wondering about end point detection because the motor has only 2 wires. If I add inline resistor to cut down motor torque, the hvac brain may not see high enough current.

A related question. How is temperature selection knob position related to blender door hinge position? Are there position sensors on the doors? I have seen some actuators with built-in position sensor, but ours have just 2 wires.


The interplay is an interesting point, that until now, I think, has not been discussed.

Our cars are filthy with these things, I think there's 4 under the dash.
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post #14 of (permalink) Old 06-09-2017, 07:21 PM
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A related question. How is temperature selection knob position related to blender door hinge position? Are there position sensors on the doors? I have seen some actuators with built-in position sensor, but ours have just 2 wires.
Here's how I think this works. With the gear reduction, the motor spins at near constant speed, when turning. The micro in the AC-controls detects when the motor stalls, as occurs when the damper reaches its travel limits. When a motor stalls, it draws excess current. A current sensor allows the micro to detect the stall condition.

The micro can, during a calibration or learning mode, determine the travel time of the damper as it moves from stalled at one end to stalled at the other.

The micro also reads the demanded damper position as a voltage determined by the slider (or wheel) on the hot/cold control, for example.

The voltage corresponds to a %-age of damper opening. For example, if the voltage varies between 1 and 5 volts as the slider is moved, and the reading is 3 V, then the slider is demanding 50% [(3-1)/(5-1)].

If the travel time for the damper is 2 seconds stop-to-stop, then the damper motor would need to be driven half that time, 1 second, from a stop limit, to get to 50%.

The micro will also keep track of where it last left the damper. Continuing the example, if the slider is then moved to 25% (2V), the micro knows to drive the motor for 0.5 secs to get the damper to 25%.

Whenever the micro loses track of where the door is (such as a result of disconnecting the battery), it simply starts driving the actuator until it senses motor stall to re-gain knowledge of the position.

Hope this makes sense.

Doug

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Last edited by plano-doug; 06-09-2017 at 07:35 PM.
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post #15 of (permalink) Old 06-09-2017, 08:40 PM
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Nice explanation! So what would cause the actuator to click when there are no gear issues (after it's been installed for a while, like in this case)? Bad microcontroller maybe?

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