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Discussion Starter · #1 ·
2008 I5 3.7 4x4

So some time ago while sitting at a stop light idling, my blower motor out of no where stopped working COMPLETELY on any fan speed so this rules out a resistor issue. I replaced my blower motor with a new one. still nothing. All fuses check out fine. Took it to a small mom and pop shop to get a diagnoses on it and they told me it was the control switch panel that has gone bad.
Purchased a new/used one and hooked it up. and it worked FLAWLESSLY on all speed settings:grin2:......for about 3 mins.:censored: ...Back to square one with the blower not working at all on any speed...What is going on here?
 

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Locate the ground splice box, mounted to the fender wall, behind the air filter case. Remove the bolt and clean the mating surfaces of the box tab and the fender wall.



If that doesn't help, find this connector, behind the right kick panel. Disconnect it and check the condition of the terminals:



If the problem persists, post back.
 

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Discussion Starter · #3 ·
So im almost positive that its not a ground splice box, I say this because as i was sitting in the parking lot about ready to replace the control unit, my old control unit still wasn't working, obviously, so as as soon as I hooked up the new one it did work, "for a short while", but am i wrong to believe that if it was a splice box, that it didn't just magically get a good connection as soon as i hooked up my new unit then decided to stop again 3 mins later without moving truck.

Oh and do i now need to buy another new control switch unit? did this blow something? is there even anything TO blow in the back of this switch? I dont want to buy another $90 dollar part to TRY and see if the problem is fixed from the other two solutions i may try JUST to find out that it didnt fix the issue and it blows ANOTHER 90$ part
 

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I envision the control box on these model year trucks are mostly just a box of switches. Can you just take an ohm meter and run some test on the unit? It does sound like something is overloading the control box.

As I don't have a truck of this era, I would need to see wiring diagrams, but a short in a main circuit, a shorted resistor to ground, could cause all fan speed selections to be dead on arrival, and might blow the new unit as well.
 

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Discussion Starter · #5 ·
Ok cary, let me run this by you,

I did remove the wiring connecting harness that connects into the bottom of my resistor to inspect it and there are a few pins (I believe it's like a 4 pin connector) in the middle of the female end that appeared to be darkened, and MILDLY appearing to be burnt out pens, but not majorly blackend and clearly burnt out like many pictures i've seen on threads of people who are experiencing similar issues but they still normally will have the highest speed setting where as i have ZERO speed setting. so this still leads me to believe it's not that connecting harness......but then again could it be?????
 

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When the blower is set on high speed, the circuit bypasses the resistor module, so you can rule that out. You are losing power or ground. The control of the system uses the ground side of the circuit. Your choice is whether you want to throw parts at it, or troubleshoot it. Do you have a test light or multimeter?
 

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Discussion Starter · #7 ·
Thanks cart, I was under that same impression. But my downfall as a mechanic is anything electrical. That's where i fall flat on my face. I am unfamiliar with a multi meter and do not even own one, but i do have a friend that does, but I wouldn't go as far as to even call him a shade tree mechanic. And what level of volts/ampers is a normal level of output would be for this unit?
 

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OK, without a wiring diagram, I am just talking in very broad terms. If you are seeing burnt terminals, something must have shorted out. I would start with cart7881's question, Do you have a meter?

I am not sure I could explain what I would do, but since you are looking at this wire harness, I would check it out first.

Someone who actually has this model truck and has troubleshot the HVAC system may be able to point you in the right direction, and i suspect cart has some ideas.

I tend to do silly things like unplug the blower motor and check for output voltage when running, etc.
 

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You can keep throwing parts at it or you can diagnose the problem first.

Check the heater circuit with a voltmeter (not ohm meter) with the fan and key on and with the fan trying to run.
http://www.naskie18.com/colorado/schematics/07_Colorado_I5/AC Heater.pdf

Cart7881 gave you the most probable failure points. Beside the two he gave you, open the grounding box and see if the pins inside are burned. That is a 3rd common failure point in that circuit.

You could also swap the fan relay and fuse with another of the same number in the fuse box. That would eliminate them as possibilities. These are not common failure items.

It only takes a few 1/10ths of an ohm in that circuit to cause the failure. Also many times it will read good under no load with an ohm meter and then open up under load. So do voltage checks with the fan powered on and failing.

There is a quick check you can do from the heater control panel. With the fan powered on, push the AC button and see that the light in the AC button illuminates. With the AC light still on, rotate the fan switch to the "O" position. The AC light should go off. If it does not go off, then you have an open in the ground side of the fan motor circuit which is where Cart7881 was trying to get you to check.
 

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My humble suggestion, get rid of that damned splice box for the ground on the fender. That thing gave me grief unimaginable with my blower for my A/C for years conking out randomly.(sometimes at the worst possible time, like the dead heat in the middle of a Louisiana summer) Once that ground pack started acting up, it never would get a good, permanent ground connection, I could move it around all day in various rotated positions near the airbox and it would never stay stable for anytime longer than a few weeks.

Finally I had enough one day and cut that POS out... So in desperation I got some wiring eyelets, cleaned up/dremeled the mating surface of the ground point and re-wired the ground leads with the eyelets back to the bolt. I have not had a issue or the blower conk out even once ever since, so don't hesitate and git'r done! Be free of this stupid GM shortsighted flaw and restore your sanity! (haha)
 

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Thanks cart, I was under that same impression. But my downfall as a mechanic is anything electrical. That's where i fall flat on my face. I am unfamiliar with a multi meter and do not even own one, but i do have a friend that does, but I wouldn't go as far as to even call him a shade tree mechanic. And what level of volts/ampers is a normal level of output would be for this unit?
First, you can get a cheap multimeter that will do 99% of what a typical shadetree mechanic needs to do at Harbor Freight. Just a few dollars, worthwhile investment for anyone.

Second, with just 12 volts of the vehicle, you are not likely to kill yourself messing with electrical. The only high voltage issues are in the ignition system and that is not where you will be playing.

Vehicle is operating off of 12 Volt DC, so set meter on DC, typically there are multiple voltage range options, 20 volts is usually where I go.

Check to see if you are getting 12 volts to blower motor with the system in the "on" position. I assume you know where the wire harness is for blower motor if you replaced it. Most likely, there is one wire to the motor, and then you have to find a ground connection to the frame. With the resistor description from cart, I have to assume that at lower speeds, the resistor reduces the voltage, so you should see something less than 12 volts, at highest setting, voltage to blower should be about 12.5 volts.

You are not going to typically be wanting to do any Amp readings in this troubleshooting - most people will just blow up there meter if they try to take an amp reading.
 

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If you replaced the blower motor yourself, you shouldn't have any problem checking the places that I posted previously. You are not the first person that has had blower motor problems, however most of the guys had some understanding of electrics. In your case, I suggest that you follow n9cv's suggestion to determine if the problem is on the ground side of the circuit. If it is a "ground" problem, you will need to find out just where it is at. The two locations that I gave you in Post #2 are the most common areas and do not require any electrical knowledge or tools to check. If you need help getting access to the connector, post back.

If the light stays on, when you accomplish the check that n9cv posted, let us know.

Oh, one more thing. It might seem that the problem is not related to what we are trying to get you to look at. Keep in mind that not all electrical problems follow common sense rules.
 

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Sorry for resurrecting an ancient thread, but i have the same issue as OP. Tested voltage at motor with key on and fan on. Get 0.35v at each position 1-3 and get -0.0v in position 4. My ac light goes out when i turn the fan to the off position.
 
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