Need some help - 1997 Tahoe Heater / Blower Motor

[east302]

The first one (heater blend door) is behind the ashtray. Pull the glovebox and you can see it. The recirc actuator is behind and above the blower against the firewall.

They each have three wires - one being the variable voltage signal from the panel to position the door and the other two being battery voltage and ground. I don’t know if they include a limit switch (there is no feedback to the control panel) so any logic is probably pretty basic and contained within the actuator.

Knock on wood, but I’ve only had one fail on my trucks (the heater one and it was an aftermarket part that the previous owner had used). I don’t remember it clicking constantly - just initially and then it would stop since it thought that it had rotated long enough to get to the right position. Actual damper position was incorrect, of course.

By watching the dial indicator on the actuator, you’ll be able to see if it’s working. It should rotate smoothly. Any erratic movement would be a red flag though cracked gears will be pretty audible and hard to miss once you’re right next to it.

 

[Mean_Green]

This is what's making the noise. I'm guessing from your description that it's the recirc actuator. Mounted to the left of the blower, sort of upside down. If I move the white door by hand, the noise reduces until the door goes back to closed (operates itself), then gets louder again. The noise stopped when I unplugged the connector (red arrow). This is with the climate control completely removed. When I plugged the climate control back in, the Recirc and AC lLEDs do not light up when I push the buttons. I can't remember if they did yesterday before I took it out or not.

I need to figure out how to remove it to test and inspect.

But why would it run constantly?

 

[Mean_Green]

One screw was already out. Got the second one out. Third one is hidden and I can't even see it to get a socket on it. I can just barely feel it with one finger.

Forgot the resistor was still unplugged. Plugged it back in and re-installed the blower motor.

LEDs on climate control buttons work again, but operation is wildly erratic, never the same thing twice when pushing a button or rotating a knob. Sometimes the blower runs, sometimes not, sometimes at different speeds.

I have one of the $50 control modules on order. Found a pack of 4 connector shells for $10 and ordered that. Should all be here next week. If it solves the door actuator issue, great, if not, I'm not sure it matters and I can just unplug the connector maybe.

I don't need to go anywhere, I don't need the blower if I do and I have another car, so it can all wait now. AC doesn't work anyways, but that's another thread.

Appreciate all the information.

 

[east302]

Yeah, that’s the recirculation actuator. The internal gears may be cracked and causing it to slip. Here’s a post where someone replaced it:

Recirc Actuator

Need some assistance - I have a 1998 silverado that has the thumping sound coming from the recirc actuator under the passenger side. I can see the lower screw to the actuator and can feel the upper screw but am having a hard time accessing it. Stealership says the dash has to be removed to...

www.gmt400.com

 

[Mean_Green]

Yeah, that's what I've been trying. I have the socket and small ratchet. Inverting your previous picture, I have screws 1 and 2 out. I can't get to 3 as it's between the actuator and what is probably the firewall. I might try with a 7/32 deepwell, but a standard and even a short extension won't squeeze in there.

I guess my question is, do I even need to? I don't drive enough that I can see ever needing recirc. Is there any reason I can't leave that disconnected? You said:

I don’t know if they include a limit switch (there is no feedback to the control panel) so any logic is probably pretty basic and contained within the actuator.

If it isn't going to cause any problems, I probably won't bother.

 

[east302]

The damper probably defaults to the fresh air position, so it wouldn’t hurt anything to just unplug it. That’s likely what I’d do if I couldn’t get that thing out otherwise.

 

[Mean_Green]

OK. I'm just getting tired of chasing after piddly stuff. As long as I can get the blower working reliably in case I need heat and defrosters in winter, I probably won't fuss with this door.

 

[Eman85]

You have encountered one of the common piddly things about GM trucks of this era. I'd like to have $1 for every one that has been disconnected and never replaced, I've done a bunch. My own truck is one of them.

 

[Mean_Green]

Connector shells look to arrive Monday. How do the pins come out? Pull the blue bar? Or pry each pin out like most Molex and Amphenol?

 

[east302]

Going by memory here, but you push the wire forward toward the end of the connector and then use a small screwdriver or pin to push in a tab to release the terminal. I think it was something like this:

Save the blue clips, the new ones didn’t come those when I ordered it.

Mine was pretty melted and brittle - some might come out by just snapping the connector apart.

 

[Mean_Green]

Yeah, OK, like typical Molex connectors.

 

[Mean_Green]

Connector shells arrived. As expected, I had to break part of the old shell since two of the pins were partially melted in place. Once removed, they looked OK though, no metal distortion from heat that I could see. Slipped into the new shell OK, all but one that I had to fight a bit for some reason. Blue bars snapped back in OK.

I was going to abandon the actuator motor until I found I could get one 'free'. Decided to try again to get it out. Had to break the far back, hidden mounting post, but it's out. Glued that post back in place to help support the new one. Strength not a major factor since no screw will be put back in. Not fighting that.

Opened it up and yes, the main gear is split.

I still don't understand how it's supposed to work though. Plugging it in and watching it, the metal center hub stops, but the motor continues to run driving the gear around the hub. If I press the Recirc button, the motor reverses, driving the hub until it stops, but the motor and gear keep running. Press the button again, the same thing happens.

No matter which way it goes, I don't see what's supposed to tell the motor to turn off. Is it just resistance? Is there something in that chip that senses the motor can't turn any more and kills power?

 

[east302]

Good question, I had wondered the same. I’ve read that the actuator uses a potentiometer, but don’t really know how that works. Does that help?

 

[Mean_Green]

No pot. Two 1/2 watt fixed resistors, two diodes, two caps and that one chip. Nothing around the metal hub to sense position either way.

Chip is marked Motorola 0372DP1 CKVN 9736 which seems to be some sort of Op Amp.

 

[exp500]

Any timers/counters on that board? pretty simple for motor pole counter. X revolutions signal change. would expect to see a trim pot though.

 

[east302]

Does the blower work at all speeds now?

 

[Mean_Green]

Any timers/counters on that board? pretty simple for motor pole counter. X revolutions signal change. would expect to see a trim pot though.

I don't see anything. If I knew for sure which pins were G, V+ and V-, I'd try to run it on the bench and see what happens.

Does the blower work at all speeds now?

New control should be here Friday.

 

[east302]

It looks like 5, 6 and 7 in the manual: battery, signal and ground, respectively.

 

[Mean_Green]

Hard to see in my picture with the shadowing, but the pins on the board are marked 5, 6 & 7.

But their terminology is confusing. 'Signal' is telling me something other than straight 12VDC is being applied and there is something other than a simple polarity reversal. Since the switches inside the control unit appear to be simple push button, lock on, lock off switches, I have to wonder if the PCM is involved somehow.

Where do 454, 1614 and 733 go?

Or maybe I'm just overthinking. I guess what I'm trying to figure out is if I have something else wrong that's just going to eat the new motor and new HVAC control.

 

[east302]

Here are the rest of the diagrams…