HVAC Nightmares!!!

[StealthTahoe]

I have an 07 LT Tahoe with the digital dual zone HVAC system with digital rear air as well. I have a couple things going on that I cant figure out.
1st- My front HVAC does not blow warm or hot air until I go to 90* then it blows hot like it should. Anything under 90* blows cool air or cold if the temp is set low. The "Auto" option doesn't seem to be working either. This is the same for both driver and passenger sides.

2nd- My rear air started off intermittently working and not working. Now it doesn't turn on at all. The display turns on at the rear panel but no air is blowing at all.

I have googled and searched without much luck or guidance. Most issues I found are older vehicles and not the same symptoms I have.

Now for what I have tried based off of internet searches.
Front- Pulled fuses for about an hour, also disconnected the battery on a subsequent attempt, to allow the system to rest. I let it do it's start up sequence every time I tried this, but nothing worked. I have no clue what to do now. ****I am not sure if the interior ambient temp sensors are working***

Rear- This really irritates me because it used to work great. I have pulled every component out of the back, blower motor resistor, blower and fan and installed them in the front. They worked fine in the front, but the front didn't work in the back, so I put them back to their original spots. I used a multi meter to check voltage and the PURPLE ( I think its purple, it's the third wire on the resistor connector) has no voltage, this is supposed to be the speed control wire. I traced this wire all the way to the drivers side kick panel and there are no breaks. I disconnected the plug in the kick panel and ran a jumper wire from the front blower motor resistor and the damn thing worked. I could fan speed on the drivers control, and heat and cooling plus head or foot vents on the rear panel.

Is there something else I can try or am I going to have to take it to the dealer for troubleshooting????
Please help!!!

 

[badandyturbo]

Have you checked the air blenders for the drivers and passengers side?

 

[nixxxster]

My 2009 have the same issue sometime. Any input fro be great.

 

[StealthTahoe]

No, I have not checked the blend doors. From what I understand there is one that you basically have to pull the dash apart to get to. I am hoping that is not the issue.

Have you checked the air blenders for the drivers and passengers side?

 

[Brian Wilson]

Blend doors are a known problem. But yours sounds more like the front control might be messed up. Just an educated guess.

 

[StealthTahoe]

SO, I realize it has been a while since my original post, but I have an update from today..... I FIXED THE DAMN A/C!!!!
For the FRONT issues, I dropped the headliner and pulled the aspirator out. At first glance, it was disgusting and covered in dust. I gently cleaned it off with canned air and a dry rag. after cleaning it, I pulled the harness through the hole and hooked the fan back up. to my surprise it worked as soon as I turned the key. At that point I put it all back together and moved to the other HVAC issue.
For the REAR issues, I ended up sitting down with my multi-meter and tracing every wire that I could from back to front. following the wiring diagram in my trusty Haynes manual I was able to narrow it down to the front climate control module due to the lack of voltage changes when I selected different things on the rear controller. At this point I pulled the controller out and proceeded to disassemble it. upon further inspection after I removed the circuit cards I found that the GREEN harness had a burned pin on..... wait for it.... the Dark Green wire that controls the rear blower motor speed. So borrowed a controller, hooked it up, and puled the HVAC fuse under the hood to perform the calibration sequence. after calibrating everything worked on both front and rear systems... needless to say I am extremely happy with myself. Other than a little time here and there I will have fixed my A/C for about $60 on a used controlled from the salvage yard instead of the $75ish an hour the dealer wanted to charge to troubleshoot the A/C with their scanner and then parts and labor.

 

[Rocket Man]

Awesome job. Perseverance paid off!

 

[2011SSVHOE]

Good job. Seventy dollars an hour is cheap around here

 

[Mp619]

SO, I realize it has been a while since my original post, but I have an update from today..... I FIXED THE DAMN A/C!!!!
For the FRONT issues, I dropped the headliner and pulled the aspirator out. At first glance, it was disgusting and covered in dust. I gently cleaned it off with canned air and a dry rag. after cleaning it, I pulled the harness through the hole and hooked the fan back up. to my surprise it worked as soon as I turned the key. At that point I put it all back together and moved to the other HVAC issue.
For the REAR issues, I ended up sitting down with my multi-meter and tracing every wire that I could from back to front. following the wiring diagram in my trusty Haynes manual I was able to narrow it down to the front climate control module due to the lack of voltage changes when I selected different things on the rear controller. At this point I pulled the controller out and proceeded to disassemble it. upon further inspection after I removed the circuit cards I found that the GREEN harness had a burned pin on..... wait for it.... the Dark Green wire that controls the rear blower motor speed. So borrowed a controller, hooked it up, and puled the HVAC fuse under the hood to perform the calibration sequence. after calibrating everything worked on both front and rear systems... needless to say I am extremely happy with myself. Other than a little time here and there I will have fixed my A/C for about $60 on a used controlled from the salvage yard instead of the $75ish an hour the dealer wanted to charge to troubleshoot the A/C with their scanner and then parts and labor.

So basically you replaced the front climate control module? I am having the rear climate control problems and i am hoping this might be the solution, i could just pick up a replacement.

 

[Mp619]

T

SO, I realize it has been a while since my original post, but I have an update from today..... I FIXED THE DAMN A/C!!!!
For the FRONT issues, I dropped the headliner and pulled the aspirator out. At first glance, it was disgusting and covered in dust. I gently cleaned it off with canned air and a dry rag. after cleaning it, I pulled the harness through the hole and hooked the fan back up. to my surprise it worked as soon as I turned the key. At that point I put it all back together and moved to the other HVAC issue.
For the REAR issues, I ended up sitting down with my multi-meter and tracing every wire that I could from back to front. following the wiring diagram in my trusty Haynes manual I was able to narrow it down to the front climate control module due to the lack of voltage changes when I selected different things on the rear controller. At this point I pulled the controller out and proceeded to disassemble it. upon further inspection after I removed the circuit cards I found that the GREEN harness had a burned pin on..... wait for it.... the Dark Green wire that controls the rear blower motor speed. So borrowed a controller, hooked it up, and puled the HVAC fuse under the hood to perform the calibration sequence. after calibrating everything worked on both front and rear systems... needless to say I am extremely happy with myself. Other than a little time here and there I will have fixed my A/C for about $60 on a used controlled from the salvage yard instead of the $75ish an hour the dealer wanted to charge to troubleshoot the A/C with their scanner and then parts and labor.

his is the part i am referring to

 

[Mp619]

T

his is the part i am referring to

Here*

 

[Rocket Man]

So basically you replaced the front climate control module? I am having the rear climate control problems and i am hoping this might be the solution, i could just pick up a replacement.

You can find used ones on EBay pretty cheap if you don't have a wrecking yard with one.

 

[Mp619]

You can find used ones on EBay pretty cheap if you don't have a wrecking yard with one.

Thanks sir, we do have a wrecker yard nearby, i'll be dropping by there tomorrow

 

[Rward]

Speaking of HVAC nightmares: I had to share this. I use forums to fix most of my problems so I thought I would return the favor.
2013 Yukon
Symptom: rear HVAC not working well, not blowing much air (heat or AC). Not sure how long she had the problem. Friend of a friend.
My assessment: blower seemed to respond to all the controls, but really no air coming through the ceiling vents. Seemed like the ductwork had an obstruction.?? Maybe blend door is stuck.
What I did next: I recalibrated the blend door actuator by disconnecting the battery, had a hops flavored foamy pop and then reconnected the battery. It didn’t fix anything.
Next step: I went to auto parts store and picked up a new blower resistor. I didn’t think this was the problem, but it was an easy thing to try... it didn’t change anything.
Other things I did. Checked fuses, pulled the rear panel all the way off and removed duct work so I could see the blend doors (all pretty easy to do) they appeared to function correctly and I did not see any obstructions.
Solution: I noticed air was blowing out the intake...??? The blower was rotating the wrong direction!!! I have no explanation for this and can not imagine why. In hindsight I wonder if it had always been this way. Anyway, I pulled the wires out of the connector that plugs into the blower and switched them to reverse the polarity and it worked perfectly. Any ideas why this happened??? The owner thinks the problem just started as the weather became colder. She is the only owner. No work was done on HVAC before. I suspect it was backwards from the factory and she just never realized it wasn’t working well. The only person to sit in the rear was her toddler and didn’t know any better.

 

[Doubeleive]

I had a similar problem this past summer I had replaced the front control with a new one because of button wear, it was plug-n-play or so I thought----, when I put it in it was hot in the California summer time so basically you have to run the temp @60 deg 24/7 to keep cool so that all worked fine, but as soon as it started to cool down this fall I started running into a problem with the rear only getting warm/hot if it was cranked all the way up to 90deg, set it for 89deg and it would blow cold. so I figured must be a bad rear blend actuator right? nope $127 later still same problem I could sit there and watch it set to 90 get hot, set to 89 go totally cold.....
so lucky me I had bought a tech2 for reasons just like this (avoiding $*** diagnostic fee's) I hooked it up and found a bunch of body codes in the hvac dcm, basically a list of 10 different errors, one of them was a open code for rear temp sensor so I thought ok here's my problem, lol tons of searches and questions later still cannot find this dam rear temp sensor. figured it must be one on the ambient sensors in the vent housings (there's like 8 of these in our trucks) checked the back 2 they checked out good with resistance and the harness had 5v so wth??? Finally I get a diagram for probably a swb escalade that showed a rear temp sensor in the headliner just like the one above the driver in the headliner. I double and triple checked my xl denali didn't have this sensor....,during my searches I had found a tsb that said if you had this list of errors (similar to what I had) then the control module should be re-programmed, not calibrated,-reprogrammed!
so at this point I just took it to the dealer and requested they flash the hvac control with the latest software, since I haven't yet programmed anything via tsweb with the tech2 I didn't want to brick my $180 control, turned out I guess the software that came on the control was for this mysterious escalade or whatever with rear temp sensor after they flashed it works perfect and no errors. so if you ever replace your hvac front control and have similar problems it could just be the firmware. I am kinda happy it happened simply because I learned a lot about how these systems work troubleshooting it.

 

[kbuskill]

I had a similar problem this past summer I had replaced the front control with a new one because of button wear, it was plug-n-play or so I thought----, when I put it in it was hot in the California summer time so basically you have to run the temp @60 deg 24/7 to keep cool so that all worked fine, but as soon as it started to cool down this fall I started running into a problem with the rear only getting warm/hot if it was cranked all the way up to 90deg, set it for 89deg and it would blow cold. so I figured must be a bad rear blend actuator right? nope $127 later still same problem I could sit there and watch it set to 90 get hot, set to 89 go totally cold.....
so lucky me I had bought a tech2 for reasons just like this (avoiding $*** diagnostic fee's) I hooked it up and found a bunch of body codes in the hvac dcm, basically a list of 10 different errors, one of them was a open code for rear temp sensor so I thought ok here's my problem, lol tons of searches and questions later still cannot find this dam rear temp sensor. figured it must be one on the ambient sensors in the vent housings (there's like 8 of these in our trucks) checked the back 2 they checked out good with resistance and the harness had 5v so wth??? Finally I get a diagram for probably a swb escalade that showed a rear temp sensor in the headliner just like the one above the driver in the headliner. I double and triple checked my xl denali didn't have this sensor....,during my searches I had found a tsb that said if you had this list of errors (similar to what I had) then the control module should be re-programmed, not calibrated,-reprogrammed!
so at this point I just took it to the dealer and requested they flash the hvac control with the latest software, since I haven't yet programmed anything via tsweb with the tech2 I didn't want to brick my $180 control, turned out I guess the software that came on the control was for this mysterious escalade or whatever with rear temp sensor after they flashed it works perfect and no errors. so if you ever replace your hvac front control and have similar problems it could just be the firmware. I am kinda happy it happened simply because I learned a lot about how these systems work troubleshooting it.

That's weird... my '08 Burb LTZ has both a front and rear ambient temp sensor... I replaced both when my front A/C started not cooling consistently. Problem solved.

 

[Doubeleive]

That's weird... my '08 Burb LTZ has both a front and rear ambient temp sensor... I replaced both when my front A/C started not cooling consistently. Problem solved.

ya when I saw the open code I looked up the part and it called for 2 so I ordered 2 but mine only use's 1 I even pulled the headliner down in the back and reached up inside as far as I could inside just to see if maybe it was hidden somewhere or if maybe the harness was just dangling but nope....must have been one of those suttle changes made like rain sensors or heated wiper fluid

 

[Airbear757]

Can you confirm that the center console controls also contains the control "computer" and that no separate module exists? I'm having multiple blend door issues and after reading your thread I think I may just replace the dash controller for $50 used instead of donating $1100 to my local Cadillac charity.

 

[swathdiver]

Can you confirm that the center console controls also contains the control "computer" and that no separate module exists? I'm having multiple blend door issues and after reading your thread I think I may just replace the dash controller for $50 used instead of donating $1100 to my local Cadillac charity.

Welcome to the forum Eric. If you can get access to a Tech-2 or other advanced scan tool, you can find out in moments what is wrong and why with your HVAC system. Without the codes and seeing what the actuators are doing, we're just guessing.

 

[Doubeleive]

Can you confirm that the center console controls also contains the control "computer" and that no separate module exists? I'm having multiple blend door issues and after reading your thread I think I may just replace the dash controller for $50 used instead of donating $1100 to my local Cadillac charity.

the center console controller is the main "brain" if you want to call it that then there is the rear controller at the back of the center console and a separate rear module inside the passenger side kick panel in the rear hvac that controls the 2 rear actuators, but that's it other than the temperature sensors throughout the system.
if you get a used controller be sure it is from the same style truck otherwise you likely will have to have it reprogrammed