Problem with rear heat

[ggeorgia]

Solved:
I struggled with the same problem on my 05 Yukon, except it was for the rear AUX heater. After lots of diagnosing and realizing there was nothing wrong with the actuator or the control module, I realized that the feedback circuit that tells the control what position the door is in was out of range. It should read between about 1 and about 4 volts depending on the position. If it reads close to zero or close to 5 volts then the acutator will stay in the extreme position and will not move. Use a volt meter and measure pin 9 of the actuator, it should be the dark blue wire. If its out of range, remove the actuator, open the acutator and reposition the gear then place something at the stops to prevent the gear or arm from allowing it to turn beyond the extreme ends. Reinstall and initialize the control by removing battery power or the HVAC fuse for about a minute. Measure pin 9 and confirm your voltage stays between 1 and 4 volts at the extreme end of door movement. Easy fix but complicated explaination. Oh and the actuator pins start at 5 and go to 10. Pin 8 should be missing if our acuators are the same. Good luck.

See pics. I used two black philips screws (pic 2) to keep the actuator gear from rotating too far. The screws are just "Stops" to keep the gear from going too far. Before the screws I had 5 volts, after I got betwen 1.2 and 4.2 volts. Remember in electronics, logical signals are never zero and 5, they are actually silghty over 0 and under 5. The screws are there because likely the door is old and over travels which causes the actuator to over travel which causes the door position voltage to go to the extreme ends during acuator calibration. see pics and good luck. What a relief to finally solve this!

Wow, thank you for the tip! I'm going to try this later this week. This is the first post I've found that identified a fix to this niche issue that seemed to affect a few people who eventually gave up on fixing it. It always inspires confidence when I see someone bust out a nice Fluke meter.

During the holidays, I had no luck after replacing the control module and actuator and variations of recalibration procedures. Just before reading your post, I bought a 3-day subscription to GM's online service manual to see if any additional/revised bulletins, info, or procedures were available since I had run out of ideas.

Alternatively, instead of manually repositioning the actuator gear to the 12'oclock default setting like you described, it seems that it would be okay to adjust it by disconnecting the actuator plug and attaching a 9V battery to pins 5 and 7. Here's the video of the procedure from ACDelco:

 

[ggeorgia]

Gabefo -- I tried your prescribed fix and the actuactor is still overtraveling and tripping the B0434 code.

Here's the summary of previous attempt to address my issue (code B0434, no rear temperature control, cold air only, actuator goes to far right position and stays there):

- replaced control module with 2 different used control modules since there are no new ones available anywhere online.
- 15185966 (pulled from Pick-N-Pull lot)
- 21997590 (bought from ebay and allegedly "tested")

- replaced actuator


I followed the official recalibration procedures as well.


The only thing I can think at this point is to wait for the latest revised control module (15832319) to become available on ebay or the new Dorman equivalent (601-036).