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2003 chevy trailblazer_lt
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Discussion Starter · #1 ·
I have an '03 LT with automatic climate control. I'm having issues with the blower running at the correct speed. I had it in Auto mode and it was 100+ in the car. The blower was on low and barely blowing any cold air. I hit the fan speed button to increase the speed and at max on the gage, it would blow a little more, but not the max. I left it in manual mode and turned off the engine. When I came back, it was still in manual mode, but the blower was putting out the max. When I got to my location, I keyed off, but the blower kept running for ~5 seconds. Next time, the blower shut off when the key was switch off. When I increase the fan speed from min to max, I would expect the fan to increase at every step, but it doesn't. It may increase on 1 or two steps, but it never reaches max.

I thought it might be the resistor pack, but I can get different fan speeds at different time, but it is unpredictable...

Any thoughts? Thanks!
 

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2005 chevy
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I have an '03 LT with automatic climate control. I'm having issues with the blower running at the correct speed. I had it in Auto mode and it was 100+ in the car. The blower was on low and barely blowing any cold air. I hit the fan speed button to increase the speed and at max on the gage, it would blow a little more, but not the max. I left it in manual mode and turned off the engine. When I came back, it was still in manual mode, but the blower was putting out the max. When I got to my location, I keyed off, but the blower kept running for ~5 seconds. Next time, the blower shut off when the key was switch off. When I increase the fan speed from min to max, I would expect the fan to increase at every step, but it doesn't. It may increase on 1 or two steps, but it never reaches max.

I thought it might be the resistor pack, but I can get different fan speeds at different time, but it is unpredictable...

Any thoughts? Thanks!
:yes: That would also be my first guess.
 

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2004 gmc
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26,181 Posts
The automatic control is an electronic module like a light dimmer in your house. Except it was designed by an incompetent designer who didn't have to submit it for professional certification like gear meant for house AC mains. :hissy:

It can fail in any sort of erratic way. If it EVER, even once, fails to stop when you turn off the ignition, it should be scheduled for replacement ASAP. It can kill your battery if it continues to run on, and once a semiconductor circuit fails like that, it never repairs itself.
 

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2004 chevy trailblazer_lt
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Is that the HVAC control module or the Blower motor control module?
HVAC control module. There's another thread that discusses the actual electronic
component most likely to be the problem. Some members have had good luck replacing
the component, but you have to like soldering... :)

Good Luck!

Chris
 

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2004 gmc
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My terms:

HVAC Control module - in the dash that your fingers touch the controls of
Blower Speed control module - hidden behind the glove box in the plenum

Pictures have been posted elsewhere of the second item that is the most likely failure point. No need for pics of the first since it's in the dash.
 

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2009 chevy
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Actually, it is called the Blower Motor Control Module.

It does the same job (controls blower speeds) as the resistor pack (the Blower Motor Resistor Assembly) in the manual HVAC systems.

Yes, it can be repaired, the FET (Field Effect Transistor) usually fails. You need some electronics knowledge to facilitate the repair; but, it can be repaired.



EDIT: Sorry Bill, I was referring to Chris' post, you got in there ahead of me.
 

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2004 chevy trailblazer_lt
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Actually, it is called the Blower Motor Control Module.

It does the same job (controls blower speeds) as the resistor pack (the Blower Motor Resistor Assembly) in the manual HVAC systems.

Yes, it can be repaired, the FET (Field Effect Transistor) usually fails. You need some electronics knowledge to facilitate the repair; but, it can be repaired.


EDIT: Sorry Bill, I was referring to Chris' post, you got in there ahead of me.
Yeah...I got fixated on the blower motor control as equates to the resistor pack.
Inaccuracy doesn't get the job done, does it.....

:bonk:

Cheers-

Chris
 

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2003 chevy trailblazer_lt
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98 Posts
Discussion Starter · #10 ·
I've found alot of good threads on replacing the module, but none on repairing the FET(s) inside... I'm intrigued... Does anyone know of any threads on that?
 

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Discussion Starter · #12 ·
Just fyi... The module is ordered and in transit. The blower staying on after I key off is getting worse. I've learned the that pressing the climate control 'off' button when the fan continues to run turns it off... Hope the new part gets here soon!
 

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Discussion Starter · #13 ·
I received the controller last week and installed it an all is good again. Thanks for the help.

I went to order 89018778, but it has been superseded to part number 89019351 by GM. The new module has 1, 5 pin connector. The supplied harness has 2 wires that go to the blower and the other wired need to be spliced into the existing harness. Here is the documentation that was included:

 

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2004 chevy trailblazer_ltz
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20 Posts
Front Blower not blowing at all 2004 TB LTZ

Would this be the same fix for my TB?

Today the front blower would not blow even though the engine was warm and the fan speed was set to high. Manually adjusting the fan speed did not make any difference The rear blower functions properly. I didnt have the erratic operation as described by others, just no blow in the front at all. When the TB was moving at 30-45 mph (on my drive home from work) there would be warm air coming out of the vents if you put your hand in front of them.

Any thoughts or confirmation will be appreciated before I order this particular part.

Thanks!
 
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