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06' TBSS LT2
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Discussion Starter · #1 ·
Just wanted to put this out there in case it hasn't been brought up before.

So I had a couple bulbs out in my hvac control unit and figured instead of sending mine out to have LEDs put in (or just replace the 2 bulbs) I'll just order up a new Dorman unit and plug it in.

Well, the unit came. Looks so nice. Plug it in. And nothing went the way it was supposed to since. The Exterior temp gauge was reading 27f all the time. It wouldn't convert the display back to the ext temp when on it would just stay on what I had it set to and the LCD display got more washed out
102536

That was "59" degrees. Junk. So I happened to have the hood opened while it was running after a wash and I noticed this lovely image
102537

Oh what a pos.

So I ordered ANOTHER one giving them the benefit of the doubt. Sure enough new one comes in - display is fantastic but it won't allow me to configure the device and defaults back to a 2006 program (mine is an 07 and 07-09 are "07" in the configuration table) so it just commands the clutch to remain engaged all the time. Including.... when the whole system is off while engine is running.

I call Dorman. On the phone for 30 minutes we ran every scenario and they conclude BOTH units I have are defective try a 3rd. F that. I said nope. Sending both back. And I grabbed up a used one from an 09 with a blown motor my buddy bought (he has several parts trucks). I plugged that unit in and IMMEDIATELY everything works as normal. Lesson here is look for a reman unit requiring a core charge vs some new Dorman junk.

This other used unit has the defroster bulb button out but its better than blowing up the whole freaking system.
 

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TrailblazerSS
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Thank you! I was just getting ready to replace mine for the exact same reason. I will do some more research and try to locate an OEM one.

Side note, did yours have any trouble with fan control? When I dial mine up to “full speed” the blower motor works for a bit, then stops as if it is overloaded. Is that related to this control, or is this a separate part?
 

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06' TBSS LT2
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Discussion Starter · #3 ·
i want to say that that is related to a relay "hi speed fan" or something like that.

found this

#6 Feb 7, 2009

Second most common failure is a relay in the resistor module. Do a search for "resistor module" and you'll find it's a relatively cheap part you can change yourself behind the glove box. Available at car parts stores - not just a dealer part. You can confirm the problem if you have a meter. The red wire on the resistor module's 7-pin connector - pin G - is 12V coming through the fuse you just changed. Pin F - orange - is the relay control and should go to 12 V when the control switch is in the HI position.

Pin A on the 2-pin blower motor connector - purple - is the input to the fan motor. Pin B - black - is ground to the fan motor.


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esu
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2006 chevy trailblazer_lt
Joined Feb 6, 2009
28 Posts
Discussion Starter • #7 Feb 9, 2009

OK,
got a warm day today so decided to pull the cover under the dash and take a look see. Turns out when I "jiggle" the multi wire plug conneceted to the resisitor assembly the hi blower comes on. Does not appear to be the individual wire but rather the assembly itself. You had said this could be replaced and not a dealer item. I guess just remove the 2 screws holding it in and bring to the local autozone?
Thx Cory
 

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'07 3SS 2WD
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i want to say that that is related to a relay "hi speed fan" or something like that.

found this
The auto climate trucks don't have a hi speed relay. The fan module is PMW control by the HVAC head unit. The fan actually has power supply and ground all the time. The HU pulses ground to the control module on the fan motor to dictate speed on the third (purple IIRC) wire. On mine, when the HU took a dump it just put the purple wire to ground all the time. Even when the key was off, the blower was on high. Killed my battery.
 
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Discussion Starter · #5 ·
awesome detailed response.

Another thing i wanted to mention was - if i didn't pop the hood to clean the engine bay off after that wash WHILE the truck was running? i would've never noticed the AC Compressor was engaged and the drier was frozen over. think about how many people who bought that dorman unit that have this happen to them and do not know that is going on (until something cracks from freezing). crazy.

I did notice that both of those dorman units defaulted to "04" configuration on the display. which works for 06 TBSS only (and others) but not 07-09.. so maybe people who have an 06 end up ok?
 

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The auto climate trucks don't have a hi speed relay. The fan module is PMW control by the HVAC head unit. The fan actually has power supply and ground all the time. The HU pulses ground to the control module on the fan motor to dictate speed on the third (purple IIRC) wire. On mine, when the HU took a dump it just put the purple wire to ground all the time. Even when the key was off, the blower was on high. Killed my battery.
So it sounds like either way the control is what’s causing my issue, correct?

2008 with Auto climate.

Anyone with an ‘07 or newer have good luck finding a new replacement that isn’t Dorman?
 

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Discussion Starter · #7 ·
Ebay and check rock auto. They have options.

There's also a guy who redoes them on YouTube. You can send to him.
 

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Dorman use to have quality products but they have went the way of a lot of manufactures starting to use off shore junk, I own a Truck repair shop when our customers stuff breaks they loose money and down time, The old saying if the wheels don't roll you don't make money is true, I have used there product for years but started to notice more and more stickesr from Taiwan and Indonesia in the last 3 years and the parts are junk. finally got to the point we had to seek other aftermarket parts and in some cases use the OEM sometime you get do get what you pay for.
 
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