97 Sonoma SLS 3 door, 2wd, 4.3 vin X, auto trans, manual heat.

New to the forum. Been chasing the problem for a while and this looks like a good place to check.

The Question: Is there a relay in the accessory circuit between the ignition switch and the fuse block? If so, where is it?

The problem: If the heater switch in the dash is turned on, the heater blower continues to run after ignition switch is turned off and key removed. All 4 blower speeds still work. Blower will turn off if the heater switch is turned off (heater and blower switches seem to be working correctly.)

Trouble shooting completed: Remover H/S blower relay. No change.
With switch off, I checked fuse panel (#6) pin, still getting power to fuse on what is supposed to be a “hot in run/acc” pin (i.e, fuse 6 feed pin.) Replaced switch. No change.
Disconnected/reconnected battery with heater switch turned off, blower does not run in any position with ignition switch off. Turn ignition on , turn heater on , blower works fine. Turn ignition off, blower continues to run.

Speculation: Sounds like a relay not resetting in the accessory circuit.

The Eternal Search: I can’t find a relay in any schematic (or behind the dash.) Did find 1 schematic (for some year GMC) that did show a “power distribution center” between the ignition switch and fuse box, but no circuitry diagram, just a box.
Alldatadiy shows a location and pinout for a “power distribution center” which seems to be the backside of the “courtesy center” in GMC drivers handbook. It contains the hazard flasher, turn signal flasher and a black box (literally, a black box) containing key, light and seatbelt buzzers, Popped the dash and took a look at it from the backside No relays (other than flashers.)

Cry for Help: Any ideas?

(BTW, I pulled the high-speed blower relay early in the process just to insure that it hadn’t malfunctioned and was back-feeding the circuit. Didn’t help.)

 

There is only one relay (right rear of engine compartment) and if you pull the correct one it interrupts power to the blower completely regardless of any other setting. If the blower still runs after that then there is a short to power on the purple wire from the relay power contact to the blower motor or a wiring hack somewhere. Unless this 97 Blazer wiring diagram does not apply to a 97 Sonoma. Even if the wiring diagram is wrong and the relay is for the high speed setting only, then the high speed setting should stop working but you said no change so something is still not right regarding the relay and/or wiring.

Regarding fuse 6 in the IPC fuse panel. You have power to this fuse with the ignition off? You replaced the ignition switch and this is still the case? What happens to the blower if you pull this fuse? That won’t effect the blower relay situation above but needs to be addressed at some point as well. The power path from the battery to that fuse is straightforward through the ignition switch with no relays. Same caveat as above regarding Blazer/Sonoma.











George

 

Thx for the quick response.
Easy Question first. Pull the fuse and blower motor doesn't work at any time.

Yep, you're right. Evidently I pulled the wrong relay because, per both your schematic and mine, ALL fan speeds go through the relay. For some reason, I was thinking that the relay only controlled the high speed fan and was only triggered when the high fan speed was selected. I failed to notice that the other 3 speeds passed through the relay on the default circuit (87a terminal on a Bosch relay.) If I had pulled the correct relay, the blower should not have worked at all.

Getting old sux.

Once I get the dash back together, I'll start pulling relays (again) and post the results.

Thanks again.

 

I suspect that the relay contacts are stuck and disconnecting the battery releases them. Once that gets straightened out then we can address the always on voltage at fuse 6.


George

 

Yep, I checked the wrong relay. 4 relays in a line, #1 & #2 connectors had been swapped. Got a new relay from O'Reilly's and it seemed to work through 3 switch cycles (blower powered off when ignition switch turned off.) 4th cycle, blower stayed on.

Still getting power to top pin of Fuse 6. Ignition switch on or off, blower relay installed or removed, probe still glows red (power.) bottom pin goes to ground (green light.) Its supposed to be a hot-in-run circuit.

Below is the Sonoma heater schematic. Similar to Blazer, but reversed right to left. What started me on the extra relay hunt was the arrow before the fuse that points to "Power Distribution Cell 10."

I'm also wondering if something else on the fuse box "Hot In Run" bus bar is supplying power (if the fuse box has a bus bar. I figure more than one circuit connects to the "hot in run" wire from the switch, hence a bus bar. Looks like my next project is to learn fuse-box circuitry.)

Any thoughts, suggestions, or ideas are appreciated.

 

Is there a time delay/review process for posts with graphic content (schematics?) Thought I'd posted a reply, but not showing up yet. In case I screwed up, here's a quick update.
Replaced CORRECT relay with new one from O'Reilly's. Problem persists. (Row of 4 relays, #1 & #2 connectors had been switched.)
Probed fuse 6 again. Top connector hot with ignition switch on or off, blower relay installed or removed. Bottom connector to ground.
Posted schematic and some questions/assumptions in disappeared post. I will repost it if it doesn't show up by tomorrow.
Really appreciate the help.

 

I am going to need some pictures/diagrams to understand your comments. What happens to the blower motor with the relay removed?

George

 

I'm sorry. I've been playing with schematics and pinouts for 6 or 8 weeks on this vehicle. (Figured I'd add power windows, door locks, mirrors, remote entry, cross-body harness and remote start while fixing this problem.) Anyway, I'm immersed in this and can be a bit sparse in my descriptions. I'll try to do better. If I don't, let me know,

With the relay removed, the blower is off in all four blower speed positions.
Ditto with the fuse removed - no power to power to blower in all four positions.
I have copy and pasted a "Blower Control, Manual" schematic from AlldataDIY.com to this post. (Tried that earlier, and the post failed. If this post fails, I'll try attaching attaching the schematic.)
What started me on the search for another relay was the arrow in the top right of the schematic pointing to "Power Distribution Cell 10" before the fuse. I see this as a connection to Power Dist. before the fuse. I may be wrong. (After I misread the blower relay circuit so badly I have added Schematic Reading to my "I Useta' Be Able To....'" List .) Like you, I was thing hanging/stuck relay and Power Distribution may have relays. No luck finding "Cell 10" on AllDataDIY site.
Next thought was "do automotive fuse boxes have bus bars?" If yes, then maybe another circuit on the Hot-In-Run bus has a stuck relay that is feeding power to the bus bar.
OK, I'm chasing ghosts again. Real world data.
Replaced high speed blower relay with battery disconnected. Reconnected battery. Turned heater switch to Heat. Cycled through blower speeds. Blower did not come on. Turned heater switch off. Turned ignition switch to "run" position. Turned heater switch to "Heat" position. Blower came on. Turned ignition switch off. Blower stopped. Turned ignition to "run"; blower came on. Repeated cycle again. Blower turned on and off when ignition turned off. (Heater switch was on "Heat" setting thru-out all cycles.) Next on/off cycle, blower stayed on. Turned heater switch to off position, blower turned off.

 

Forgot to thank you before sending the last post.
Thank you.

 

So did you replace the blower relay (all speeds, not high speed) with a new one?

It sounds like everything works as it should.


George