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DanielJones
DanielJones, ASE Certified Technician
Category: GM
Satisfied Customers: 498
Experience:  GM A Tech at Straub Buick GMC
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GM Silverado: I have a 2004 Chevy 2500HD Duramax. My Heat/Air

Customer Question

I have a 2004 Chevy 2500HD Duramax. My Heat/Air isn't working. I have auto climate controls. I have changed the head unit, I have changed control module, cant find a bad fuse, and the blower motor/fan works if I plug it into my wifes car. Here is the strange part when I put a test light to the purple/input wire occasionally that causes the fan to start working.
Submitted: 7 months ago.
Category: GM
Expert:  Gary replied 7 months ago.
do you have a good multi meter on hand ?
Customer: replied 7 months ago.
yes.
Expert:  Gary replied 7 months ago.
with everything plugged in back probing the resistor module terminals with the meter set to DC black meter lead into the block wire that does NOT do to the blower motor and the red lead to the red wire terminal what does it read with the key ON and the blower off then when you turn on the blower to high what will it read ?
Customer: replied 7 months ago.
Is seems to read right around 12v consistently, rather key is on, off, blower on high or low.
Expert:  Gary replied 7 months ago.
do you have any wires or jumper wires around ?can you leave everything plugged in and truck on with the blower set to high and stick the wire into the back of the black wire terminal at the resistor module the black that does NOT go to the blower motor then run the other end of that wire to a good ground confirmed ground will the blower run ?
Customer: replied 7 months ago.
Ran a jumper from the black wire going into the module to a bolt on the frame and no blower.
Expert:  Gary replied 7 months ago.
ok if you change that ground you made to back probe the black terminal at the blower connector will it run ?
Customer: replied 7 months ago.
Yes is I use my ground, and back probe the blower, its works. Definitely on high.
Expert:  Gary replied 7 months ago.
so by adding a ground to the black wire terminal at the blower motor connector makes it work fine ?
Customer: replied 7 months ago.
Yes.
Expert:  Gary replied 7 months ago.
and the resistor module is brand new ?
Expert:  Gary replied 7 months ago.
with it jumped like that will the blower control operate correctly or just be on high all the time no matter what you select for fan speed ?
Customer: replied 7 months ago.
Yes just got it off Amazon. My old one would cause the fan to run non-stop even with the truck off. I must admit when pulling the old one out the Red and Purple wire touched causing a spark. No the fan just runs at full speed it seems.
Expert:  Gary replied 7 months ago.
if the red is 12 volts and the black is a good ground can you see what the purple/white wire reads when the blower is set to high and then what does it read when set to low ?
Customer: replied 7 months ago.
The purple just seems to read 12v no matter what the setting
Expert:  Gary replied 7 months ago.
if you unplug the module and test it 12 volts all the time ? are you 100 % sure on this ?
Customer: replied 7 months ago.
I will unplug the module a test it that way. one minute
Expert:  Gary replied 7 months ago.
ok
Customer: replied 7 months ago.
Maybe I was mistaken, after unplugging the module I am not getting any juice to the purple wire regardless of speed setting.
Expert:  Gary replied 7 months ago.
not even 2 volts with the truck on and the blower set to high ?
Customer: replied 7 months ago.
Completely dead
Expert:  Gary replied 7 months ago.
that should send close to 5 volts on high then 0 when offat the back of the controller is it still showing 0 volts ?
Customer: replied 7 months ago.
So back probe the purple and white wire at the back of the control unit?
Expert:  Gary replied 7 months ago.
yes
Customer: replied 7 months ago.
Nothing is coming out of the purple wire while back probing at the head unit.
Expert:  Gary replied 7 months ago.
can you check in the under hood fuse box and be sure the fuse HVAC a 10 amp fuse is good and in the inside fuse box the fuse HVAC is good ?if you plug in your old controller will it run at high speed ?
Customer: replied 7 months ago.
I plugged the old controller in and still nothing out of the purple wire, I will check the fuses.
Expert:  Gary replied 7 months ago.
ok
Customer: replied 7 months ago.
checked both fuses and are fine. still nothing out the purple wire. I know it doesn't make sense but there was a couple times when I was putting a test light to the purple wire at the module and the blower would start moving.
Expert:  Gary replied 7 months ago.
lets see if another expert has any ideashang on another expert will reply back to you
Expert:  DanielJones replied 7 months ago.
Hello. Welcome to the site. Thanks for coming. I'm ***** *****. I'm here to provide as much information and insight as I can, to best answer your question.Can you give me your VIN# ***** I can see if there are any Service Bulletins?Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
1GCHK23274F252093 . So I plugged the module back in, and get 12v at the module no matter what the setting, but its still reading zero at the control unit. Seems strange.
Expert:  DanielJones replied 7 months ago.
Did you check all 3 fuses?
Customer: replied 7 months ago.
I checked the HVAC 10 amp under the hood, the 10amp HVAC in the truck, and the 30amp Heat/AC in the truck.
Expert:  DanielJones replied 7 months ago.
There should be a 40amp Blower under the hood.
Expert:  DanielJones replied 7 months ago.
Here is the diagram If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
The blower fuse is good. So where do I go from here?
Expert:  DanielJones replied 7 months ago.
You replaced the blower resistor/module?
Customer: replied 7 months ago.
Yes its brand new along with the control unit.
Expert:  DanielJones replied 7 months ago.
This issue may occur if the blower motor speed is set to any speed position, except for low, when the key is turned off.Try setting the speed to low, turn key off and retry it.
Customer: replied 7 months ago.
Tried it. Still getting zero volts when back probing the purple/white at the control unit, and getting 12v when back probing at the module.
Customer: replied 7 months ago.
Are we done?
Expert:  DanielJones replied 7 months ago.
no.
Expert:  DanielJones replied 7 months ago.
Did you try plugging it in and seeing if it worked?
Expert:  DanielJones replied 7 months ago.
Here is the GM diagnostic procedure for checking the system. If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
Purple /white wire is still dead coming from control unit almost seems like a fuse issue but all fuses test good. Maybe I am just doomed to have no HVAC in this truck.
Expert:  DanielJones replied 7 months ago.
There is a bulletin for this issue but involves a GM module. It could be the same thing with the aftermarket part. If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
Control module and blower motor are good I believe. Maybe the head unit is my issue even though I replaced that as well, but without any juice to the purple wire I don't know what else to do.
Expert:  DanielJones replied 7 months ago.
Try checking it by the diagnostic chart using a test light and meter.
Customer: replied 7 months ago.
Do you have a wiring diagram for the climate control unit?
Expert:  DanielJones replied 7 months ago.
Here
Expert:  DanielJones replied 7 months ago.
HVAC Connector End Views
Expert:  DanielJones replied 7 months ago.
If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
Thank you. So still no reading back probing the purple/white at the control unit. When everything is plugged in I get 12v while back probing Both wires that plug into the blower, but if I ground the black wire the blower runs at full speed. So do I have a bad ground somewhere before the control unit?
Expert:  DanielJones replied 7 months ago.
Which black wire are you grounding and where are you connecting it to?What condition is the plug terminals in that plugs into the resistor/module?
Customer: replied 7 months ago.
The plug itself is new, came with the new module. I misspoke the wires coming from the new module to the blower motor are purple and orange, if I jump the purple to a good ground the blower works, on high only. The purple and red wires coming from the new module are reading 12v always.
Customer: replied 7 months ago.
Not sure if this may help but the back on the control unit gets really hot once the grey harness is plugged in.
Expert:  DanielJones replied 7 months ago.
What problem were you having before you replaced everything?
Customer: replied 7 months ago.
Only had the truck for 2 weeks, blower has never worked. I changed the module and the blower would then run all the time even when the truck was off. Then when trying to figure that out the red and purple wires touched causing a spark. I thought maybe a burnt something up in the head unit so I got a new one of those, but still nothing. So I don't know if I fryed a wire somewhere else. Sorry, to be such a hassle.
Expert:  DanielJones replied 7 months ago.
The red and purple wires coming out of the resistor/module?
Customer: replied 7 months ago.
Yes
Expert:  DanielJones replied 7 months ago.
It looks like you might have fried the module, I would return it and see if they will give you another one. Don't tell them you touched the wires together. If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
Will do.
Expert:  DanielJones replied 7 months ago.
Let me know how you make out.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
Just a little concerned why I'm I don't get any power to purple wire from the control unit.
Expert:  DanielJones replied 7 months ago.
Did you try checking with a test light?
Customer: replied 7 months ago.
I haven't put a test light but I get zero volts with the multimeter. But I'll put a test light to it and get a new module and then I'll rate and close the issue.
Expert:  DanielJones replied 7 months ago.
OK.Make sure the part they gave you is the crossover # ***** this GM Part # ***** If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.If you are satisfied with the information I supplied we would like to close out this question.If you have no follow-ups at this time, please remember to Rate My Service.Follow ups are free after ratings, so rate in confidence!Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****
Customer: replied 7 months ago.
Second new module didn't do any good. I took the dash apart even farther and there is a small 8 pin harness just dangling behind the jockey box, and the passenger side junction box looks like it might be missing a harness don't know if maybe these are part of the issue.
Expert:  DanielJones replied 7 months ago.
What color wires are in the harness?Can you upload a picture of harness and location?
Customer: replied 7 months ago.
Hope this helps again thanks for sticking with it.
Expert:  DanielJones replied 7 months ago.
Can you take a picture of the end view of the connector?
Customer: replied 7 months ago.
And if we can figure this issue out I will gladly pay whatever it takes.
Expert:  DanielJones replied 7 months ago.
I don't see that connector in any of the HVAC connector's.Try checking it by the diagnostic chart using a test light and meter. Make sure you use the appropriate tester the step say's to.
Customer: replied 7 months ago.
So I should be getting some kind of voltage reading from the purple/white wire coming out of the control unit?
Expert:  DanielJones replied 7 months ago.
The HVAC control module provides a pulse width modulated (PWM) signal to the blower motor through the blower motor speed control circuit. The blower motor changes speed based on the received PWM signal from the HVAC control module. Power and ground are provided to the blower motor through the battery positive voltage and ground circuits. 1. Turn OFF the ignition.2. Disconnect the blower motor connector.3. Turn ON the ignition, with the engine OFF.4. Connect a test lamp between the blower motor supply voltage circuit and the blower motor ground circuit.5. Place the blower motor switch in the maximum speed position. 6. Place the air temperature switch to the warmest position.Does the test lamp illuminate?
Customer: replied 7 months ago.
No it doesn't light up
Expert:  DanielJones replied 7 months ago.
1. Disconnect the blower motor control processor.2. Connect a test lamp between the battery positive voltage circuit(RED) and the ground circuit(BLACK) of the blower motor control processor.Does the test lamp illuminate?
Customer: replied 7 months ago.
Is the blower motor processor the same as the module?
Customer: replied 7 months ago.
Yes it illuminates
Expert:  DanielJones replied 7 months ago.
The blower motor processor is the thing mounted next to the blower motor. Connect a volt meter between the blower motor speed control circuit(Purple/White) and the battery positive voltage circuit(RED) of the blower motor control processor.Observe the volt meter.Place the blower motor switch from the minimum speed position to the maximum speed position.Does the voltage increase when the blower speed is increased?
Customer: replied 7 months ago.
I get no reading on the purple when it's unplugged from the speed control module no matter the speed and once plugged into the module I get a little above 12v no matter the speed. The Red gives me 12v consistently.
Expert:  DanielJones replied 7 months ago.
Are you testing for voltage from the purple to the red?
Customer: replied 7 months ago.
So from my volt meter hook one probe to red and one to purple?
Expert:  DanielJones replied 7 months ago.
Yes. Red probe to Purple/White wire and black probe to red wire.
Customer: replied 7 months ago.
Ok back probed the red and purple going into the module and got no voltage reading. If I switched purple to black and red to red I got maybe 1v no matter the speed setting
Expert:  DanielJones replied 7 months ago.
Connect a volt meter between the blower motor speed control circuit(Purple/White) and ground.Observe the volt meter.Place the blower motor switch from the minimum speed position to the maximum speed position.Does the voltage increase when the blower speed is increased?
Customer: replied 7 months ago.
No when it's plugged into the module I get 12v regardless of speed setting. If it's unplugged I get nothing.
Expert:  DanielJones replied 7 months ago.
I am going to look over all your data again and see what I can figure out. I will get back to you. Thank you for posting your question.Your business is very valuable to us.Thank You ***** *****