AJatx

There is a strange low frequency whirring sound underneath the dash near the glove compartment. The noise has been associated with my lack of cold A/C with my automated HVAC controls.

I've done some searching on the forums and found some folks experiencing a sound or noise like the one I've been hearing, but nothing really addressed my issue. I was going to clean out the blower but the air has been blowing out vents. It has been mentioned in a few threads and probably a good thing to do.

However, the humming noise comes from another area, not the blower. I disconnected the blower and you can still hear the sound. In fact, when I disconnect the air mix control solenoid, the noise goes away. The noise is in fact the little motor trying to push the air mix control armature. The arm is stuck at the mid-point of the arc (connecting arm track has an arc shape).

I played with temperature control with HVAC on auto-mode. Setting it to COLD and pushing the arm toward the driver side let the arm move. Voila! I have cold air blowing through my vents.
Raising the temperature to a hotter setting (about 88F), the armature moves to the passenger side. The arm stops moving about midway and you can hear the sound (stepper motor trying to pull/push the armature, but cannot).

Hopefully, the stepper motor life isn't shorten from being stuck (current still driving the motor when it's stuck). It's definitely still working but something is binding the arm or the stepper motor driving gear is somewhat stripped.
I tend to think it's the arm getting stuck somehow since I did install an aftermarket stereo head unit.

There is still grease on the arc'd path of the connecting arm.

For now, I'm happy to have cold air blowing in the truck again.
However, I need to fix the mixer. It looks like a lot of work to remove the dash components to get to the mixer assembly.

Anybody have experience with removing the mixer assembly or fixing this issue? I noticed my google search brought up some TSB with more recent Toyota/Lexus models that may have issues with their air mix control components.

J

MTL_4runner

The limiteds do have a servo control for each of the different functions where other basic models have sliders/cable linkages. The best thing to do would be to try and disconnect the servo motor from the linkage and verify by hand if you can move the duct lever such that there are no places it binds causing the servo to get stuck. If you don't find any binding, you'll probably have to replace the servo. If it does bind, you'll need to investigate further and remedy that problem.

Not sure if it is either of these two servo pics:

AJatx

Thanks, Jamie.

The arm linkage is not binding since with a little effort, I can make the servo swing either direction. The mid point is probably the most stressful point for the servo. Removing the servo assembly is going to be PITA.

The assembly is actually 90 clockwise offset compared to what I see under the dash.
The most difficult thing about removal will be the arm linkages. The armature from the servo has a lock nut on it and some washers. It looks like I need to remove the stereo/HVAC controls and ashtray to have easier access to the main armature that goes from the arc link to the actually long arm linkage. I'll post some pics later today for others to see what I'm referring.

Always something with my rig these days, but one task at a time, I'll get my truck back to tip top.

J

AJatx

Here is a pic of the mixer arm control servo. It's immediately above the passenger side lower heater duct.

I pushed the arm so it would be on the AC side and not hot side. Since it's summer in Texas, I should be fine with the AC.

Anybody have experience pulling this servo assembly out? There are a couple of linkages involved and it looks like the best way (without breaking anything) is to remove the center console.

J