06 Yukon REAR HVAC won't shut off -update, WAS resistor - SOLVED

[TJ Baker]

So I did depin the center pin during testing

I just went out and depinned it and plugged it in, so purple was not connected and it still runs

I totally agree it has to be the resistor, but I've tried 3 different ones all with the same result, they just free-flow the input voltage to the motor output and I've tested that before even plugging the blower in so I wouldn't think it's a blower issue

I do have a 4th resistor on the way that was more expensive maybe it'll work but I'm gonna wire up the hot and grounds externally before putting in the vehicle to see if I get the same result with the output voltage for the blower side being the same as the input side from the car

It bears repeating... Have you verified that your replacements are getting the power, ground, and control input to the locations designated on the new speed control?

Here are a pair of diagrams. one has the 12 volt battery power at terminal A and the other has it at terminal C.

 

[Edwards1337]

It bears repeating... Have you verified that your replacements are getting the power, ground, and control input to the locations designated on the new speed control?

Here are a pair of diagrams. one has the 12 volt battery power at terminal A and the other has it at terminal C.


View attachment 489317


View attachment 489316

So on the oe resistor it shows 12v hot at pin c. The new ones don't have a diagram on them

However for ***** and gets I just swapped the pins a and c and have the same issue, once I plug it in the blower comes right on.

 

[mikez71]

Even with purple wire disconnected?
Really does seem like the blower module.. but 3 bad ones in a row?!

 

[Edwards1337]

Even with purple wire disconnected?
Really does seem like the blower module.. but 3 bad ones in a row?!

Make it 4 lol

Starting to feel defeated on it, can't wrap my head around it. When it's plugged in the ONLY way to get it off is unplug it or pull 30a rear hvac fuse under the hood... can unplug everything else and it just runs, unplugged bcm still runs

Next trip to junk yard the only other piece I can try is overhead hvac controller, which as stated prior it runs even with that unplugged, also runs with rear hvac module next to blower unhooked

Can't wrap my head around it. Ground is good, I've got virtually no resistance on the ground line back to the battery, ran a ground direct to battery just cause to test, still nothing

For now I'm just gonna break the 12v orange wire upfront with a relay triggered via ignition + a switch just so I can leave it hooked up and turn it on whenever my kids are in the back, just gonna blow on high but atleast it'll shut off with my switch or when I turn the key off

 

[mikez71]

HVAC control module auxilary?

Looks like that is located further forward on the rear HVAC, next to one of the actuators...
Guessing that is the orange wire you are talking about, 10A ECC fuse?

I know you tested the purple wire, but you said it reads a steady 9V when plugged into blower module. I guess the meter has different impedence than the blower module input?

 

[Fless]

I may have missed it but are you working on manual HVAC or AUTO HVAC (with digital temp on the head)? Wiring diagrams are different, of course.

 

[Edwards1337]

I may have missed it but are you working on manual HVAC or AUTO HVAC (with digital temp on the head)? Wiring diagrams are different, of course.

Auto

However you guys won't believe this shit

I traced every wire, properly tested each circuit to verify I had everything front to back and replaced every linked component

I went to the junk yard today and grabbed a upper console control, lower hvac control, rear console control, rear hvac module, blower motor, resistor, and both harnesses, full front to back through the headliner to the fuse box, ran me just shy of 150$

New upper controls, no go
New blower motor, no go
Draped the harness over the truck, no go
Said screw it lets try this resistor

******* worked. Blower didn't run and fan control is working at the front unit

I have no logical explanation for why 5 new resistors didn't work, all labeled and marked for my truck, rear, auto hvac controls

The junkyard OEM resistor fixed it, can't believe that shit

 

[mikez71]

Wow! I'm even more scared of new replacement parts now..
Amazing they all failed the same way.. I wonder how many defective ones are out there..

Way to power through it!

 

[TJ Baker]

However you guys won't believe this shit

I believe it,,, see my post #11.

I have no logical explanation for why 5 new resistors didn't work,

They are not properly manufactured for your rear Blower control system. I would say their application listing is incorrect.

Good to hear you got it working now.

 

[Joseph Garcia]

I'm super happy for you. GREAT troubleshooting work, even though it was a royal PIA for you, and took way more time and money than you wanted, to resolve this issue.

There's always a positive coming out of experiences like this, though they are sometimes really hard to see. Knowledge is power.

Look at it this way, you now know WAY more about your truck's HVAC system, and will be able to assist others on this Forum, when they have related issues.

 

[TJ Baker]

Amazing they all failed the same way.. I wonder how many defective ones are out there..

I wouldn't say they failed or are defective.

I think they simply are not the correct design for this vehicle, regardless of what they are labelled or sold as.

 

[mikez71]

Maybe an incorrect listing, but how many other GM vehicles have a rear blower?
I doubt it was the manual version, as there is an extra connector and the resistor looks different..

Perhaps one factory supplied them all, and they have a screwup in production..

Just noticed, the front and rear use the same blower module in the automatic system..

 

[Edwards1337]

I believe it,,, see my post #11.




They are not properly manufactured for your rear Blower control system. I would say their application listing is incorrect.

Good to hear you got it working now.

Ya that's why I kept buying from different brands and sellers and all listings would mention rear auto ac only and such

 

[Edwards1337]

Maybe an incorrect listing, but how many other GM vehicles have a rear blower?
I doubt it was the manual version, as there is an extra connector and the resistor looks different..

Perhaps one factory supplied them all, and they have a screwup in production..

Just noticed, the front and rear use the same blower module in the automatic system..

The parts I got came from a 2003 yukon slt but it seems all full size GM SUVs had rear air system, whether they are all auto or not I'm not sure

But every resistor looked similar but I did open them up and did see some differences from one to another

 

[TJ Baker]

The parts I got came from a 2003 yukon slt but it seems all full size GM SUVs had rear air system, whether they are all auto or not I'm not sure

But every resistor looked similar but I did open them up and did see some differences from one to another

For my own curiosity, did your original have a smaller/shorter heat sink than most of the replacements seen online?

On mine most all of the replacements I saw online when looking for one showed a heat sink that looked like the one on the front blowers speed module. These physically will not fit on my 2005 Yukon because the larger heat sink hits piping inside the cabinet.

 

[mikez71]

Interesting..

Rockauto shows the same blower module for Yukon XL front and back..(and suburban)
But not the short Yukon, which shows a staggered heatsink for the rear..