Still working on HVAC problem

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ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#13827 Closed 2004 GMC Sierra 1500 SLT public

The passenger side door is still giving me problems. I did your checks and found a bad connection at the new blend door servo that was causing erratic counts and I have repaired that but still the passenger side will not go to cool. My mechanic installed a new control head unit and had it programmed with the latest software update but it remains the same.
I was able to get a good knockoff of a Tech 2 scanner. I can see the counts of the doors as the controls are moved from full cold to full hot the drives side goes from 32 counts to 255 counts just fine and what is being called for. The passengers side goes from 255 counts to 128 counts and the head unit never calls for anything less than 128 counts. When I do the recal procedure I see both doors go the full range of counts as the calibration happens but after you turn the engine off and restart the passengers side calls for 128 counts and the blend door module goes to about half way in it’s range. Could this be a sensor problem on the passengers side air duct? I see that there are several sensors in the ducts on the wiring diagram for the HVAC system. Any other ideas? Both my mechanic and I are really stumped on this. He is a GM mechanic working free lance now and has never seen anything like this.

I used the scan tool to look at the sensor data and it looks about the same for both sides. I used the scan tool to manually drive the actuators and the drivers side goes from 0 to 265. The passengers side goes from 265 to 128. Then used the scan tool to do a reset of the control module and after the reset I tuned the truck off and restarted. without touching the controls the passenger side is calling for 128 counts and the actuator is reading 2 counts. If I touch the control the actuator moves to 128 counts and will not go lower.

Sparky

I am attaching wiring diagrams #1
Sparky

#2
Sparky

Can you take screen shots of some of the data and upload the images? I would like to see the duct temperature readings along with sunload.

Here is a screen shot of the sensor data. I did not see a value for the sun load sensor per say I do see a dim at 83% which is changes to 100% if I take the truck out of the dark garage.

Here are the door positions. Just don’t understand why the commanded counts only goes to 128? That is about half way between full heat and full cold.
Sparky

Since the command seems to be stuck at 128 counts we have to assume at this point that the control head is seeing some sort of data that is throwing it into a default setting of some sort.

Looks like the BCM is attached to  the solar sensor and sends serial data to the PCM and the HVAC module. You may have to look in the other modules to see any relevant data.

I will do some more research for a possible answer to this problem.

Thanks I do appreciate you taking the time to look into this problem. it seems to have everyone I talked to stumped even GM techs.

I scanned the BCM. Both sun load sensors are reading 4.5 volts on a sunny day with not a lot of heat today. I tried covering the sensor the headlight went on and the reading on the sun load sensors stayed at 4.5 volts. I scanned a few other things and the only strange thing I found is that the transmission sensor is read -40 degrees? The tuck had been driven about 10 miles and had only been sitting for about 15 min. So that seems odd to me.
Sparky

The transmission temperature sensor reading so low does need to be fixed but should have no relevance to the temperature door issue.
Sparky

Okay, here is a theory. I ran into one case where writer stated that there was a faulty ground to the actuator and it caused the feedback voltage to go well above the normal zero to five volt range. In essence changing the operating range of the actuator’s position sensor. I am a little skeptical of the cause but it did get me thinking about the five volt position signal possibly going outside the normal operating range and the control head over compensating.  So my next step would be to back probe  the voltage readings at the actuator and at the control panel.The signal wire would be the Dark Blue wire. The ground I mentioned earlier would be the Yellow wire.

 

I found no references anywhere with the counts being stuck at 128 or even close.

Okay thanks I will check the voltage at the control head and see what I find. I too have been searching the web and could not find anything related to counts stuck at 128. It has to be something strange as we have swapped control heads and re-flashed the new head and the HVAC system does the same thing.

Hi, Sorry its taken me this long to get back to you. The voltage at 128 counts 2.29 volts at 243 counts 4.38 volts and when I do a re-cal though the Tech 2 the door actually drives to zero counts even though the requested counts stays at 128 the voltage is zero.
When I use the tech 2 to manually drive the mix doors the passenger side turn off goes to a minimum 128 count on 224 counts the drivers side command off 67 counts and command on counts 224 counts.
I have no idea if this was the case the mechanic saw as he was chasing a bad connection at the actuator which I found. I am wondering if the new Dorman control head is defective? I am thinking about ordering a new one and trying it.
Any thoughts?
Sparky

Assuming that your voltage readings were taken at the rear of the HVAC control panel then I would recommend installing a new HVAC control panel and strongly recommend using the ACDelco brand.

Yes the voltages were tested at the control head wiring connector with it connected into the HVAC control. My mechanic was not able to get a Delco control. The local dealer told him they are no longer made. I will look around and see if I can get a AC Delco control head.
Thanks for your time with this problem.

Sparky

ACDelco part number 15-72956.  Looks like they are about to go obsolete. Still a few at my local warehouse that we buy from for $250. Don’t know if that is a good price or not?

I have been looking into the panel. It’s a little to much for me to spend right now. I will have to wait for a while until I have the cash.
Thanks,

Matt

Hi,

Can you post the wiring diagrams again? I was going to try and print them out but I can’t seem to get to them any longer.
Thanks,

Matt

I ordered a new control head today real AC Delco part. I will let you know if anything changes with the new control after I install it.
Thanks.

I was not able to get a new control the place I ordered it from called and did not have any left in stock. I went to a local wrecker yard who had a 2004 GMC Sierra as a parts vehicle. They started it up and I was able to try out the control and it worked fine so I took it. I installed it in my truck and it threw error code B0418 and B0229. The drivers side door works fine as usual but the passengers side just stays at full hot. 245 counts and I can’t command it. I even tried removing the connector to the actuator for the passengers side and connecting it to a actuator that I have that works fine on the drivers side just hanging there not actually connected to the blend door. I clear the error code and it comes back. The count reading is stuck at 245 counts. Each time I did a reset of the error codes and a recalibrate of the door actuators from the Tech 2. At this point I am totally lost??? I am thinking that it maybe a problem with the door wiring harness.
Any thoughts?
Sparky

Well at least you seem to have gotten past the 128 count issue and you are now getting trouble codes. The B0418 code is related to a problem with the passenger side temperature door actuator and the B0229 is for the air inlet door actuator but you already know that. If both codes return each time the codes are cleared then the diagnosis goes back to a series of continuity, load,and drag tests of the wires and terminals between the control head and the listed actuator. I am pretty sure you stated somewhere along the way that a new dealer supplied actuator had been installed and that you had tightened the terminals at the actuator connector. Can you reconfirm this?

Also have you checked and or cleaned the connectors at the passenger side junction block behind the right dash end panel?

I did tighten the pins on the HVAC actuator connector, I also checked the connectors at the right side of the dash. I used a good cleaner on them as well. The counts are erratic from the new actuator in the dash. I think I need to go back in and replace it with a better actuator at this point. The ones I bought were not dealer I got them from rock auto and they were not the most expensive ones nor are they AC Delco. I hat to take the dash apart again but if this is going to get repaired I need to get a real AC Delco actuator and install it. if that doesn’t fix it then it would have to be the wiring or some connector I think.
Sparky

Since you do have a scan tool to read the door position data I would maneuver the harness around at several points to see if I could induce movement or steady up the readings.  If you can replacing the actuator will probably do no good. If you cannot then a quality ACDelco part would likely fix your problem. Make sure you order the correct part number for your truck if you do replace it.

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