http://www.wellsve.com/ This video demonstrates how to read the wiring diagram for a GM vehicle blower motor and use that knowledge to diagnose a failed blow…
GM Blower Motor Resistor Diagnostics by Wells
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Hello. I have an issue with my 2008 ford expedition. The blower motor would only work on level 1 and 2 (low speeds), any higher and the motor shuts off. Do you think I too should get the ac motor resistor replaced? Thanks a ton.
Yes, I believe you are right Jeff! Nice catch.
Mark Hicks
Wells Vehicle Electronics
The only yellow connectors in a GM vehicle are SIR related.
On my buick pa it dosent even blow air on any speed it is auto. I took the piece and it cost from 180-360 at dealer to replace. Smh. I hope this fixes it.
Have no idea, it was unplugged before we worked on it. I believe it is for some sort of accessory.
Mark Hicks
Wells Vehicle Electronics
What was that unplugged yellow plug by the blower?
3. Increase the fan speed setting from low to high while watching the voltage. The voltage should increase to nearly 5 volts as the fan speed setting is increased to high speed.
4. If the voltage increases to near 5 volts in step 4, and the terminal for the Purple and White wire is tight at the blower motor control module, replace the blower motor control module.
Hope this helps
Mark Hicks
Wells Vehicle Electronics
Sorry for the slow reply … your vehicle also has issue with the Blower motor control module BMCM. It is unusual to just have the middle speeds. here is a test procedure:
1. Test for ground on the Black wire in terminal C at the blower motor control module.
2. Connect a voltmeter from battery positive to the Purple and White wire in terminal B at the blower motor control module.
Mark,
I have a 2003 Trailblazer. The fan will not run on setting 1 or 5. Do you think it might be the resistor or something else?
Thanks,
Mike
You are welcome. Let me know if you need anything more.
Mark Hicks
Wells Vehicle Electronics
BINGO! – you’re a gentleman and a scholar Mike. Off to look for a replacement control head (couldn’t find anything loose). Thank You VERY VERY much!…
1. Remove the HVAC control head but keep the connectors plugged in.
2. Back probe and ground the Gray/Black wire at pin H at the control head. There is a Green/Yellow wire next to it.
3. If the blower motor now comes on check for a poor connection at the control head.
4. If OK replace the control head.
The blower motor should draw less than 15 amps running, or it can greatly shorten the life of the blower module.
Hope this helps. Stay in touch
Mark Hicks
Wells Vehicle Electronics
Hi Mark – Thanks for the very qiuick reply – here’s so far… Resistor is new, blower works (when hooked up straight to battery), have ground continuity at blower plug but no power with controller at any speed including high. No fuses show short/blown. ???
Well your vehicle has both and more, please let me explain. It has a blower motor resistor and two blower motor relays. One relay for high speed and one for the other speeds. What is wrong? If you give me this information, I might be able to give a most common failure and a diagnostic procedure.
Mark Hicks
Wells Vehicle Electronics
Question: Is there a blower motor relay (not resistor) on a 1992 Buick LaSabre Custom – and if so where is it? Thanks!
thwack from tree wick likes stuff from themen strife tested gnix frumpings,cause those would be in due time!
Leave me a message on my channel with your e-mail address and I will send you the instructions.
Be sure to also leave the year, make, model and engine size.
Mark Hicks
Wells Vehicle Electronics
I have a 2003 chevy venture that the medium fan setting does not work I have been told the resistor is located on the driver side and hard to get to . I am disabled on SSDI and would like to know how to replace it.
Thanks
@markjhicks
Thanks Mark for the comment. I never learned to play base but they say if I really want to know how a song is played to try to listen to the base in the song. I’ve been playing on/off since 1991 but if I take out all the breaks where I didn’t play it probably would amount to about 3 solid years lmao.
… 2001 was the last year for the 4.3 Trailblazer. The 4.2 is a 6 cylinder and they also offered the 5.3 8 cylinder.
Mark
That TrailBlazer is a 4.2L? Is it a V-6? My 2000 GMC has the 4.3L high output V-6 witch leads me to believe its a large bore 6.
Cool, thanks Mark. I will see you tomorrow morning on the Podcast with. Eric & Rich.
I honestly have no idea. I suggest contacting a local salvage yard, they should know the answer.
Mark Hicks
Wells Vehicle Electronics
will a blower motor from an olds alero fit on a pontiac sunfire?
Good to hear … I am going to work on that STAY TUNED!
Mark
Absolutely, Mark. The theory is what carries the day, ultimately….
I am impressed another great question!! You correct when the internal windings short to each other the internal resistance will drop. If we remember Ohm’s law, if the resistance drops and the voltage supply stays constant the amperage must increase. This is what happens to not only a blower motor but anything with a winding of wire.What do you and everyone else think about us producing a few videos on electrical diagnosis with some theroy in them?
Mark Hicks
Wells
When the blower motor draws too much amperage it has to be because it’s internal resistance has fallen. Is it accurate to assume that there is an internal short within the blower motor that allows current to pass more easily through the motor? Of course it can’t be a short to ground, just to adjacent wires within the motor coil, allowing current to pass with less resistance. Is there any other explanation for why resistance would fall? Thanks for posting your video.
Very good point and completely true. It also helps to confirm the 23 – 24 amps the blower motor was drawing was too high the circuit. In the future I hope we can show more of what happens to a circuit that is drawing too much current and how to diagnose it. It happens more than most know.
Thank you for the great tip.
Mark Hicks
Wells Vehicle Electronics
Something I’d like to mention is that a general rule of thumb is that the load of an electrical circuit should consume roughly 1/2 the amperage, give or take, that the fuse for that circuit is rated for. Example, circuit that has a 10 amp fuse, whatever load, be it injectors, fan motor, whatever the case may be, is on that circuit should consume around 5 amps.
Great Diagnosis.
good tips.