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2001 Chevy 1500HD, Blower Motor Inop, Help

knightgang on Tue October 19, 2010 9:12 PM User is offline

Year: 2001
Make: Chevy
Model: 1500HD
Engine Size: 6.0
Refrigerant Type: 134a
Ambient Temp: na
Pressure Low: na
Pressure High: na
Country of Origin: United States

I have a 2001 Chevy 1500 HD, 4x4, 6.0 ltr with Auto Climate Control. Everything was fine one day and the next, the blower motor would not work. I usually leave the AC on, either on Auto or with the fan control about 1/2 to 3/4 the way turned up. On this particular day, someone else drove my truck and the turned off the AC using the Fan control knob turned to off. When I got in and turned the AC back on, the compressor kicked on, but the blower motor would not work. After several days of trying to trouble shoot, I finally straight wired the blower motor with a switch to get through the summer, now I need to fix it before it gets cold so that I can have heater. Here is what I have done, tried so far.

1st thought was the blower motor module was bad. Bought a brand new one off of E-bay. No dice, motor still not working. (Again, with 12V direct it works just fine).

2nd, tested the voltage at the plug that goes into the blower motor module. I get 12v across the orange wire and the black wire, then I get .01 to .05 volts across the black and the grey/white depending on the position of the fan control switch.

3rd, with the blower motor plugged in and testing at the plug that goes into the Blower motor, I get .08 volts ragardless of fan switch position.

4th, I have disassembled the AC Control head and cleaned inside the fan control switch, no change.

At this point, I feel like the control head is bad, but at $135 new (cheapest I can fine) or even $85 used, I want to be sure that is the problem before I spend the money. Is there any other advice you have for me or other testing to be done to be certain it is the control head that is bad. Bear in mind, all other functions work just fine, blend door, Fresh air/Recirculate, Vent/Defrost deflector door, etc. Only the blower motor will not work while plugged in to the system as it should be.

Please help...

NickD on Wed October 20, 2010 3:01 PM User is offline

Just replying because no one else did, unfamiliar with your system but ACC is no secret to me. Always seen push buttons to manually advance or retard the blower, does this by playing with the pulse width modulation fed to the blower motor module.

With the module in my hand and a circuit diagram, and emulate all the operations on my bench to make sure its the culprit before taking it apart and repairing it. Emulate the BCM output with a pulse generator. Say repair because I refuse to pay 150-250 bucks for a module that only needs a blown out N-Channel Power MOSFET transistor that costs about 17 cents, but normally use one that cost 19 cents so it will last a little longer. Least I have some control over this, getting screwed by our government is something I have no control over, getting screwed by one organization is enough, only have one butt.

So what did you get from ebay, an empty case? Not knocking ebay, did buy a couple of broken notebook computers to get parts to repair my broken one, really lucked out, got enough parts to make two good ones. Also lucked out in buying broken car radios for parts, just about the only place you can get them. But with way overpriced electronic modules for vehicles, prefer buying locally so after pretesting them and learn I just purchased a piece of crap, I can return them. I don't pay attention to those signs that say no returns on electronic modules, can even show what's wrong with them.

You must have a BCM that controls that module, I switch my AC off all the time, 3 miles before I get home so the evaporator is dried out, switching off an AC should not hurt the system. Never has for me, you have some other kind of problem. Yeah, my job went to China, no longer have access to my old companies alldata database, so can't look it up. So why am I replying? Not helping you at all. Must be bored.

JACK ADAMS on Wed October 20, 2010 3:48 PM User is offline

I would check all your fuses first! Also was the blower control module bad? GM offers a repair harness that needs to be replaced if the module is burnt.

Good luck!

mk378 on Wed October 20, 2010 3:50 PM User is offline

I think it is PWM like Nick says, you should have more voltage on the gray / white wire from the control head. It's a series of pulses that increase in % on time as the speed setting is increased. The blower module amplifies those pulses up to the tens of amps needed to spin the motor. We'll presume it's good since you tried another one-- apparently the input pulses are not there.

Disconnect battery, unplug blower module and check gray / white wire for continuity to the control head and shorts to ground. If that's OK pull the control head and look inside for bad solder or obvious burnt parts. If there's a short to ground from the gray / white wire only when the control head is plugged in (and no power since battery is disconnected), the component in the control head that drives that wire is probably blown.

knightgang on Wed October 20, 2010 4:57 PM User is offline

Already pulled the control head and pocked around inside. Foudn no bad solders, sodler joints or resitors, etc. Also, pulled the fan switch appart and tried to clean the surfaces inside, to no avail. Still not working. Will try the continuity test tonight, that is the one thing I have not done, however I do get varying voltage at the grey/white, just not near enough according to the below information... I get between .01 and .05 volts. Below they state a min of .4 volts to 4 volts to the module...

This is the response I got from another Forum. Gonna try this little trick tonight. I assume it will work, can anyone confirm...


The Orange is 12V as you've found out.
The Black is ground as you've found out.
The Gray w/ Bk is a "LOGIC" wire. It should generate between .4V at the lowest speed setting, and 4V at the highest. If that voltage isn't there and changing, you've got a bad HVAC controller (control panel).

As a last resort, piggy back connect a AA battery (because it's only 1.5 Volts) across the black and the Gray w/ Bk (Black being the (-) negative of your AA battery) while the truck is running. It should put the blower on medium/low. If it then blows, you definitely need the HVAC controller.

Edited: Wed October 20, 2010 at 5:01 PM by knightgang

JACK ADAMS on Wed October 20, 2010 5:36 PM User is offline

Your e-bay part, blower controller (resister); was it New or Used? Was your old one burnt inside the plug terminals?

Also do you know if you have any stored codes or pending codes on the PCM?

Edited: Wed October 20, 2010 at 5:43 PM by JACK ADAMS

NickD on Wed October 20, 2010 6:38 PM User is offline

The Orange is 12V as you've found out. The Black is ground as you've found out. The Gray w/ Bk is a "LOGIC" wire.

Sure sounds typical of other GM blower modules, but don't see a wire listed from the module to the blower motor, kind of important as well as that orange wire is typically always hot, has a 30 amp fuse in series with it where the module is simply in series with the motor. By touching that orange wire to the motor wire, the motor should run, can even do this with the module attached as you are bypassing it.

What is typical of these things if the module does short out, more typical, the motor runs continuously even with the ignition key in your pocket.

Can only assume that .4 volts to 4 volts is the average voltage reading for the "logic", this is far more typical, as that pass transistor is switched hard on and hard off. If a battery did work, would have to be linear, but insufficient to switch on those pass transistors or could partially turn them on and burn them out. In a linear controller, the module could dissipate as high as 167 watts where its only about 15 watts maximum in the switch mode of operation. With the former, that would have to be one huge module to dissipate that kind of power, really doubt that is what you have. Logic levels were typically five volts, really don't know about yours but could find out in a couple of seconds if I had the vehicle.

So this guy is saying that logic signal is coming from the HVAC controller, can't dispute that either, but was always from the BMC. If that burns out, kind of expensive to replace.

You really can't tell if a chip transistor is opened or shorted just by looking at it, unless it is fried to hell.

knightgang on Thu October 21, 2010 8:37 AM User is offline

[quote=heymccall;4049616]As a last resort, piggy back connect a AA battery (because it's only 1.5 Volts) across the black and the Gray w/ Bk (Black being the (-) negative of your AA battery) while the truck is running. It should put the blower on medium/low. If it then blows, you definitely need the HVAC controller.[/quote]

Before doing this, I checked the continuity of the grey w/ black wire back up to the control head. It is good. Shaved back some insulation on the black and the grey/black wire to get the AA battery in the circuit, no dice. Still no action form the blower when hooked up in this fashion. I know the blower will work with full 12V applied, I ran it that way all summer, but it started melting inline switches.

At this point, I am stummped. Is it realy the control head, is it the blower motor? Do I have another bad Module? Don't have the money to replace all three. Somethings gotta give...

NickD on Thu October 21, 2010 9:30 AM User is offline

GM blower motors are throwaway items, have been that way for the last 30 or so used. Cold roll steel armature shafts that rust within the limited lubricated bronze bearings, shorted turns in the armature, worn brushes if everything else is good. Can't take them apart, but should rev up quickly and with the blower wheel firmly attached, came that way, heat melted on, should draw no more than 22 amps in open air.

Even at that, they are the best replacements you can buy from any aftermarket blower I have seen to date, seem to last about 80K miles. Aftermarket motors I have tested only pull about 15 amps, incapable of getting full blower speed when you need it. Then look even cheaper on the inside.

With any blown module I have seen, they blow far below that 30 amp fuse that is suppose to protect, the culprit is the blower motor itself.

Maybe I went over your head between the difference between a linear and a switching blower motor, really highly doubt if yours is linear in which case, that 1.5 volt cell could do more damage than good by partially turning on the pass transistors. Typically, logic levels are 5 volts, applying five volts would switch it on hard with no damage. But has been some talk about reducing the logic levels to 3 volts, so would want to be sure about that before advising. An instant peek at a circuit diagram would tell me that.

mk378 on Thu October 21, 2010 10:38 AM User is offline

Test the motor and power circuit by unplugging module and jumping orange wire to black wire. Motor should come on full speed. I think it will do that even with the key off. That proves motor, fuse, etc. are OK. Like Jack said, be sure connector is not burnt so it makes good connection to module.

I think you're going to need to hit the module with more than 1.5 V to turn it on. Five volts should do it. The module will have an on / off action. The control panel rapidly pulses the module (and motor) on and off to run less than full speed.

If the module will turn on, and the wiring is OK, then that only leaves the control panel. Assuming the other functions and display work it would be an internal failure and not something like lack of power supply to the panel.

knightgang on Thu October 21, 2010 2:02 PM User is offline

Good, I have a way to jump the motor off of the orange and black by-passing the module. I know the motor itself was working because I had it running straightwired at a full 12volts all summer. I also am getting 12V between the orange and black wire going into the module, so I know I have power there.

I will test the blower off of the orange and black and try to bump the pulse volts to the module to see if I can get it to kick on and run the system, thereby then proving that the Control head is bad.


NickD on Fri October 22, 2010 7:38 AM User is offline

An oscilloscope is the best tool to verify that logic output, but a voltmeter should at least tell you, you are getting a greater voltage than zero at the output. That voltage should increase as your fan control setting speeds increase. Don't have to use the process of elimination, just measure it.

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