Rear Fan/Climate Controls for XL Not Working

[CaptainXL]

I have been having an issue getting the rear controls in the second row to work. When I switch the knob up by the shifter to "R" I get no control at the rear for fan speed/mode or temp. I did a quick search on the "old" website and found the thread below. That thread kind of fizzled out and the OP was left guessing. I am left stuck wondering which part to get. Is it a actuator module that is the culprit?

blower motor resistor - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

 

[djthumper]

If none of the controls in the rear are working I would see if 12V is getting back to that panel. When the front switch is set to R it should send a 12V signal to the rear controls to operate. With that said you may want to check your connections at the front switch as well.

 

[CaptainXL]

I have been having an issue getting the rear controls in the second row to work. When I switch the knob up by the shifter to "R" I get no control at the rear for fan speed/mode or temp. I did a quick search on the "old" website and found the thread below. That thread kind of fizzled out and the OP was left guessing. I am left stuck wondering which part to get. Is it a actuator module that is the culprit?

blower motor resistor - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

Well the HVAC fuse under the seat is good. I am going to test for power there and at the control. If nothing shows up there I am going to suspect the rotating switch is faulty. Will have to check for power there.

 

[Blckshdw]

If the rear system works properly from manipulating the front controls, I would think the problem is in the neighborhood of the rear seat controls. Long shot, but when the parking lights are on, does the rear seat controls light up as well? If not, then that's a sure fire way to know there's a problem back there.

 

[The_Roadie]

...when the parking lights are on, does the rear seat controls light up as well? If not, then that's a sure fire way to know there's a problem back there.

That's a good idea, and works on the DDM and PDM modules in the doors, where GM saved a wire and the modules have a local dimming control for their lights, and the BCM tells the DDM/PDM what intensity to put the lights at by a serial data message. But in the case of the HVAC control modules and many other dashboard switches and modules, the lamps are separately powered up by a "dimming supply bus". That means (against most folks expectations) the module can lose its 12V power, fail to operate, but the display still lights up. Sneaky GM design.

Check for power at the control connector for sure, but don't always accept lamp function as a clue that the module will also function.

 

[TB2k4]

If the rear system works properly from manipulating the front controls, I would think the problem is in the neighborhood of the rear seat controls. Long shot, but when the parking lights are on, does the rear seat controls light up as well? If not, then that's a sure fire way to know there's a problem back there.

don't know if yours worked in the past. but i had a similar problem that i discovered when i replaced the speakers. i ended up just popping the interface out of the console and unplugging it, then replugging it- should work if the problem is extemely centralized like mine was. probably not THE solution, but definately an easy, cheap beginning.

 

[neelskit]

I have been having an issue getting the rear controls in the second row to work. When I switch the knob up by the shifter to "R" I get no control at the rear for fan speed/mode or temp.

Do you have manual or automatic (digital) HVAC controls?

 

[The_Roadie]

Do you have manual or automatic (digital) HVAC controls?

How does affect the answer? I'm not near my schematics at the moment, but I'm pretty sure that no matter what system you have up front, the rear seat controls for the XL are the same. I may be wrong.

 

[neelskit]

...but I'm pretty sure that no matter what system you have up front, the rear seat controls for the XL are the same. I may be wrong.

If you have the manual HVAC system, the rear control head will consist of three knobs- fan speed, temp, and mode. If you have the automatic system, the rear control head will consist of a digital display with soft buttons to adjust as well as an "auto" mode. The wiring appears to be the same- a reference signal sent from the rear control module, through the front override switch, then back to the rear control module. I was curious (assuming the OP has the digital system) if the rear control head display behaves as if it has control or if it shows the "locked out" message.

 

[CaptainXL]

If you have the manual HVAC system, the rear control head will consist of three knobs- fan speed, temp, and mode. If you have the automatic system, the rear control head will consist of a digital display with soft buttons to adjust as well as an "auto" mode. The wiring appears to be the same- a reference signal sent from the rear control module, through the front override switch, then back to the rear control module. I was curious (assuming the OP has the digital system) if the rear control head display behaves as if it has control or if it shows the "locked out" message.

It is the manual HVAC system with the three knobs. Will continue to troubleshoot power tonight. Seems easy enough as the control just pops out. Will also check power at the fuse panel. which wire is the power wire and control wire from the front switch? I need to check for power at both.

 

[neelskit]

It is the manual HVAC system with the three knobs. Will continue to troubleshoot power tonight. Seems easy enough as the control just pops out. Will also check power at the fuse panel. which wire is the power wire and control wire from the front switch? I need to check for power at both.

If the rear system works when using the front controls, it IS getting power. The reference signal to the front override switch is grey and the return signal from the switch to the rear control module is yellow. I would suspect a bad switch. Good luck!