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Discussion Starter · #1 ·
Hello all,

The car in question is my 2012 R/T Plus w/ STP (M6). It has single zone HVAC with no modifications that would affect it.

About 6 weeks ago, my battery began to show it's age and I decided to replace it with a new one. From the first start afterwards, my rear defrost light flashed on cold-start. I thought little of it initially, despite attempting to "calibrate" the blend doors via the battery/fuse disconnect method outlined in the forums.

Fast forward 3 weeks - During my morning commute I noticed that I had absolutely zero heat on a 35 degree morning. I gloved up and dealt with it for a day or two, before getting enough time off to diagnose the issue. The blend door behind the steering column had apparently failed. It would click, but no movement was visible. I replaced the actuator with an AutoZone brand (Duralast, IIRC), which restored my heat... for the most part. The actuator would not move until I turned the heat to the 74 degree mark, at which point it equated to roughly 60 degrees. I spent a few weeks driving around with the temperature set just below maximum to stay moderately comfortable.

After giving up the mechanic life for a number of years, I no longer possessed a bi-directional scan tool. I had a local shop attempt to calibrate the blend doors for me, only to discover that it was prompting them with an error and refusing to calibrate. Rather than pay a lofty diagnostic fee, I shopped around for bi-directional scan-tools and decided to give AlfaOBD a try. I also purchased the recommended OBDLink MX+ module. The software is awesome, I'm beyond impressed with the capability given the price point. It's no $4,000 scan tool, but it's easily the equal of the $1-1,200 models and then some.

Anyways, with that tangent out of the way... I attempted to test the blend doors via AlfaOBD, only to have it partially complete the process and then stop unexpectedly. I have run it over a dozen times, to the same effect. My first instinct was that the AutoZone blend door actuator was the issue. I ordered a used (but functional) actuator from eBay and ran through the same diagnostics to the same effect. I even took the time to re-connect the ORIGINAL actuator (which turns, weakly), only to confirm that all 3 resulted in the same issue. From the 56* mark all the way to the 72* mark, NOTHING happens whatsoever. The 72* mark is registering as the 56* mark is supposed to, while each interval through the maximum temperature is doing the same.

I played around with the monitoring function of AlfaOBD in the hope that the dial/potentiometer was the culprit. I was surprised to find that it (apparently) functions as it should. Now that I am out of ideas, I figured that I would reach out to you fine folks in the hope that you can point me in the right direction. I love this car, but I'm beginning to miss my early 90s sh*tboxes with their cable driven blend doors. I'm pretty accomplished when it comes to diagnosing mechanical failures, but electrical is my weakness. I have attached screenshots of my diagnostic attempt, it should be helpful for somebody more knowledgeable in this realm. Thank you in advance!!!

The only error code that presents - I cleared it multiple times and it persists:
Font Screenshot Material property Rectangle Number
A graphical display of the full range of the temp dial/potentiometer, overlaid with the target and actual positions of the actuator in real-time.
Light Product Rectangle Slope Font
The individual positions of the temp dial/potentiometer, at each interval from coldest to warmest.
Product Rectangle Font Screenshot Material property Product Rectangle Font Screenshot Material property Rectangle Font Line Screenshot Red Rectangle Font Slope Line Red Product Rectangle Font Line Red Product Rectangle Font Line Red Product Rectangle Font Line Red Product Rectangle Slope Font Line
 

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Discussion Starter · #2 ·
This SCREAMS calibration to me. Every instinct in my body says that it should be a simple fix - unfortunately, both a local shop (with a Snap-On bi-directional scan tool) and my own efforts to calibrate it have ended in failure. AlfaOBD didn't give an error code, it simply rotated all of the actuators and then stopped after a few minutes, without saying "complete" afterwards. The flashing defrost light persists, along with the calibration issue. I'm hoping that I simply missed something obvious...
 

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This SCREAMS calibration to me. Every instinct in my body says that it should be a simple fix - unfortunately, both a local shop (with a Snap-On bi-directional scan tool) and my own efforts to calibrate it have ended in failure. AlfaOBD didn't give an error code, it simply rotated all of the actuators and then stopped after a few minutes, without saying "complete" afterwards. The flashing defrost light persists, along with the calibration issue. I'm hoping that I simply missed something obvious...
Hey there, your trouble code for the in-car temp sensor fan may very well be part of your problem. I would suggest you start with that.

Did you happen to have the knee panel below the steering column removed at some point? If so I would make sure the sensor is connected properly.
 

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Discussion Starter · #4 ·
Hey there, your trouble code for the in-car temp sensor fan may very well be part of your problem. I would suggest you start with that.

Did you happen to have the knee panel below the steering column removed at some point? If so I would make sure the sensor is connected properly.
Thank you for your reply!

I suspected that it might, unfortunately I've had no luck even identifying that. The last time I chased HVAC issues of any sort in a vehicle, the most advanced part of the system was the A/C. Give me engines and transmissions all day long over these electrical gremlins...

I have owned the car since early 2016; I never removed anything beneath the dash prior to this month. It is still out of the car at the moment, only so that I don't have to risk damaging the tabs while tracking this down.
 

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Exactly, it may need just that. Disconnect battery, set everything to match what the car thinks it is, then reconnect it.
 

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Discussion Starter · #7 ·
Thank you for the reply, fellas.

I found that thread a while back; I attempted that multiple times, both with the fuses pulled and with the battery disconnected. Prior to buying AlfaOBD, I went through that process over a dozen times.
 

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Discussion Starter · #8 ·
Alrighty, so I realized that the DTC was me being stupid. I left the panel beneath the steering column off because I was still actively toying with this. Replacing the interior temp sensor cleared the code, but did NOT resolve the other issue.

After attempting to calibrate the doors multiple times w/ AlfaOBD and via disconnecting the battery, I was able to get the car to recognize about 2/3 of the temperature dial. It started at ~64 degrees, then worked all the way up to the maximum. I drove it for a day like that, then attempted to calibrate it again... back to square one, it only recognizes "72 degrees" as the full-cold position again.
 
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