Blower motor troubles

[1998_K1500_Sub]

I couldn’t help with bypassing it, but here are two things that may be worth checking:

1. Is the connector that plugs into the blower switch at the panel melted or damaged? With the blower on, move the connector around to see if the blower stops. It could be a loose or bent female terminal (or whatever they’re called) in the connector.

2. The blower ground wire connection is attached directly to the blower housing. With the blower on, move it around and see if it’s loose.

Your symptoms mimic those that I saw when the connector was melted in my 98.

^^^ this

Everything @workingonit said points to a poor electrical connection. Somewhere, in proximity to where @workingonit strikes the panel (and the blower responds), is the poor connection.

"Poor" could mean the connector itself is loose or oxidized, as noted by @east302.

"Poor" could also mean the wiring has been compromised in some way, although this is less likely than a poor connector.

@workingonit, the wiring diagrams / wire color codes are available in the service manuals, and they can be found here:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

@east302, didn't you post the wiring for the blower circuit recently, in another thread?

 

[east302]

It was in post #2 of this thread. Should the connector be the culprit, these are what I used on my 98 - Delphi #12064998.

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[workingonit]

I couldn’t help with bypassing it, but here are two things that may be worth checking:

1. Is the connector that plugs into the blower switch at the panel melted or damaged? With the blower on, move the connector around to see if the blower stops. It could be a loose or bent female terminal (or whatever they’re called) in the connector.

2. The blower ground wire connection is attached directly to the blower housing. With the blower on, move it around and see if it’s loose.

Your symptoms mimic those that I saw when the connector was melted in my 98.

"Bypassing" some circuit is my usual way to fix a problem I can't resolve, or that others (the "expert" technicians at my old job) made worse. I love to tinker, and/or save money by make-do workarounds, but I'd prefer to leave my wife's GMC (her backup vehicle, and gardening & antiquing items hauler) factory, and not have to worry about her misusing or failing to monitor the circuits I added or modified (she has a history of both, on two other vehicles, that ended-up badly for both).

When I changed out the first control panel, I didn't notice any melting or damage, but it may be present anyway. And the blower ground is also something I should've already checked, but haven't so far. I'll check both connections tomorrow, before it rains again. I have to work on my vehicles outside on sand & gravel, because the wife's Lexus, our mowers & outdoor tools, and my homebuilt 4x8 squareback camping trailer preclude me from working in the rain!

I'll also check the amperage draw at the blower motor; I never had a DC amp clamp before, but now I've got an AstroAI Digital Clamp Meter, that I recently bought when working on the BMW's fan speed project. If the blower is drawing more than 17 amps (a figure I've seen on many forums as a max reading for these blowers), then I'll replace it again.

I might just run a secondary ground while I'm under there; I had an intermittent fuel pump relay problem on my old '86 S10, that'd only act up at night, 50-100 miles from home, and usually in the rain...it confounded me for quite awhile, until I added a second new ground, just for giggles. The problem went away, and never returned. I'd guess that the '98 GMC might have a few grounds that might need attention, too (all the unpainted metal underdash is very rusty).

Thanks for your reply...it's encouraging to get a quick response here, since my posts/queries on some other forums are largely ignored, until the problem is fixed, or the problem(s) persists long-term.

 

[workingonit]

WOW, two more replies while I was eating lunch and composing my reply to east302. Thanks to all; I have a lot to look at and wiggle a few wires, after reading your responses. Now, I have hope for a fix! In my nearly 59 years of working on cars, this problem has perplexed me the longest.

 

[1998_K1500_Sub]

In my nearly 59 years of working on cars, this problem has perplexed me the longest.

Something I learned long ago and has remained true since is that a large percentage of electrical problems are related to a physical connection that's deteriorated / no longer effective.

Write that on your garage wall

This is never more obvious than when a physical attack alters the device's behavior.

Dual inline pin ICs mounted in cheap sockets (e.g,. as used in the Apple II computer) are notorious for this behavior. Example: Slamming the Apple II on the desktop would restore it to proper operation. A college professor showed me that fix, he used it routinely.

Connectors that have been overused / overheated / exposed to corrosive elements can be troublesome.

Insert your experience here:

 

[Schurkey]

If you have an "amp clamp" suitable for low-amperage loads (less than 60 or 80 amperes) the next thing you need is an oscilloscope.

You can then freeze the 'scope pattern, examine the waveform...and discover the amperage draw of each bar of the motor's armature. Once you figure out how many bars the armature has, you can calculate the motor's RPM.

Amperage draw, and motor RPM are not likely to be in the service manual specs. You'll have to test "known-good" motors of all sorts to build your own database.

Fuel pumps, HVAC blower motors, radio antenna retraction motors, window motors...test 'em all, write-down the figures.

Ancient Snap-On Counselor II automotive 'scope, testing a K1500 fuel pump.

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Cursors picking out repeating pattern of armature bars. This fuel pump has eight armature bars. Time between repetition is 9.42 miliseconds. 60,000 divided by 9.42 = 6369 rpm. Peak amperage draw is 6.889 amps.

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[workingonit]

I watch a lot of YouTube auto-diagnostics guys, particularly Pine Hollow Auto Diagnostics and South Main Auto (from a list of 20 or so), and eventually would like to get a cheap 'scope to check suspect component waveforms, but time and money aren't on my side.

At almost 74, I'll probably not have the time (or learning time) to be able to diagnose via a 'scope, or, since I'm probably only going to be working on my cars (99% sure), it would be a waste of time and money (at least that's what the CFO "wife" will say). But, maybe I'll sneak in a cheapo 2-probe 'scope into my tool kits.

My collection of tools keeps growing, yet my younger relatives are completely non-automotive in their interests...so whom am I supposed to hand them down to?, much like my elders had no automotive interests either, therefore I received no instructions nor tools from them, excepting my maternal Grandpa, prior to his early-onset Alzheimers.

 

[1998_K1500_Sub]

You can then freeze the 'scope pattern, examine the waveform...and discover the amperage draw of each bar of the motor's armature. Once you figure out how many bars the armature has, you can calculate the motor's RPM.

This method, described by @Schurkey, also allows one see failure of the commutator or individual motor windings, e.g., the current draw (the "sawtooth" in @Schurkey's images) will not be consistent across the 'scope trace; there will be disparities where poor commutator performance / winding failure occurs.

@Schurkey used a storage 'scope in his example, but an analog 'scope can do almost the same thing by manually adjusting the sweep time to match the motor period, so as to "freeze" the waveform on the display.

I occasionally check my fuel pumps (on my various autos) in this way to gauge their electrical health. As @Schurkey noted, the same method can be applied to many automotive motors (as well as others, such as electric hand tools).

I use the Fluke Y8100 AC/DC Current Probe.

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