HVAC control weirdness...

[Pinger]

Two things on my 1999 Suburban I can't figure out.

The linkage that controls the face level door seems to be jamming up the operation of that actuator. For a while the face level vents wouldn't work. When I pulled at the arm on the door it freed - but the linkage came apart (at the spring). Re-assembled the linkage and if I try and reconnect it to the door arm it is too long and wont clip together. It is around an 1/8'' too long. If I reconnect in a different position everything is fine until I switch to demister and the face level linkage seems to jam up and prevent the actuator from reaching the demister position. With the face level linkage disconnected, the demister setting works fine.
Is it possible to re-assemble that linkage wrong? Does it matter which side each plate sits?

The other thing going on is the demister setting (with the face level linkage disconnected so it cannot bind as outlined above) is only available with the blower setting at Lo or higher. In the Off position the actuator arm moves to the position it does for foot well vents. Is this normal? Is it just a default position switched to when the blower is switched off (for whatever reason?).

 

[AK49BWL]

To answer your last question, yes floor-venting is the default position for system-off. I guess I'd need to see pictures of the linkage at the point where it's binding to know for sure where to go from here.

 

[east302]

Here are the linkages in the dash vent position, maybe it will help.

You must be registered for see images attach

 

[Schurkey]

I can't help except to say that there's no better time to replace that crappy foam, or to pull the actuators apart for cleaning and inspection (or replacement) than right now. Supposedly, the plastic gears inside the actuators get brittle.

The foam, in particular, caused me unlimited grief for about two years. Foam rotted between the cowl/firewall and the plastic of the HVAC fan box. Seemed like the heater didn't work, but in fact it was a cold-air leak into the cabin that totally offset the heat from the heater. 30 miles at highway speed, and the cabin was so cold I had to wear a snowmobile suit. Tore the dash apart, replaced the foam with generic home-improvement-store weatherstripping foam, and all is well in that department.

 

[Pinger]

To answer your last question, yes floor-venting is the default position for system-off. I guess I'd need to see pictures of the linkage at the point where it's binding to know for sure where to go from here.

In the photo in post #3, the face level vent is closed with the arm in the high position rotated ACW and the linkage at its maximum height. When I try to reconnect the linkage with the components as per the photo, the pin (that goes through the hole in the arm) is above the arm by an amount that allows it clear the arm. With no freedom to compress (only extend) the linkage it doesn't reconnect.
When I re-arrange the positions so that it can be reconnected the mechanism then binds at the position in the photo - the actuator arm can't push from its 12 O clock position to 1 O clock, cant push through its TDC.
The 'pin' on that arm on mine is different from on the demister linkage which makes me think someone has been there before me. The system was working before. Then the face level vents were erratic then ceased altogether - the point at which the linkage came apart when I pulled on the face level door's arm and from there I have the problem as described. I've just looked at it again and I have reassembled the linkage wrongly. The upper part should face the driver side - on mine it's passenger side. Away to swap it and see what happens.

 

[Pinger]

I've just looked at it again and I have reassembled the linkage wrongly. The upper part should face the driver side - on mine it's passenger side. Away to swap it and see what happens.

And... it's all working again. There's a protruding pip on the passenger side of the part of the linkage that connects to the actuator which must have been interfering with the part that connects to the door arm when assembled on the wrong side.
Thanks all.

 

[AK49BWL]

Glad you got it fixed!

 

[Pinger]

Glad you got it fixed!

Thanks. What really helped were the two photos posted (inc the one from you on the other thread). I guess I'd have tried reversing the linkage just to see, but having photos to reference how it's supposed to be certainly helps.