Hey folks. I've got a '93 Buick Lesabre, and among other issues, the front vents never have airflow; just the Defrost and floor vents. When pressing the 'vent' option on the controls, nothing happens, airflow just stays at those two vents.

I've checked the engine bay for vacuum leaks; all the connections are good, nothing is disconnected, there'* good vacuum when I disconnect the line from the vacuum tank. I also went into the cab on the passengers side and disconnected the 4 colored vacuum lines from the control unit they connect to and individually tested for vacuum; they were all good.

Most people say that when there'* a vacuum leak, the system defaults to Defrost, which would make sense. But as far as I can tell all vacuum connections are fine.

There'* a motor in behind the glove box that, I assume, is what changes the temperature (when the temp on the controls is changed, the motor opens or closes), and it functions fine. It switches between hot or cold smoothly. Is there another motor that control the front vent doors?

It'* also worth mentioning that the climate controls function fine; air speed and temperature sliders work fine and the airflow responds, it just doesn't want to send air out of the front vents.

I'm pretty well stumped, as I've tried everything I can find. Any suggestions?

Thanks!

Here are some pictures. The first is of the motor that controls temperature behind the glove box.


Third is what kind of climate control it has, if that helps at all.

not being that familiar with the car, i would guess there has to be another actuator for position just by having buttons instead of a dial or slider

A faulty HVAC head unit will also default to defrost.

I think I've narrowed it down to two things. Either the primary climate controls, or the vacuum valve Solenoid.

I applied vacuum to each hose; defrost, vent, bi level and defog. When vacuum was applied to each hose, the airflow change was obvious and functioning as normal.

When having everything set up normally, when pressing settings on the climate control I can feel the solenoids in the control valve opening and closing; there'* an audible noise and I can feel the vibrations. But it doesn't change the airflow as it should, especially when setting it to 'vent' (it literally does nothing)

The climate control is intermittent; sometimes it'll turn on and other times it will turn off. After replacing this, would the only thing left to replace be the control valve?

It seems to me that it'* either the main control or the valve. I have to replace the primary climate control anyways, so it seems it'll be easy to figure out what comes next.

Any other input would be great.

Thanks!

From your description, it sounds like a vac solenoid box which controls the vac to each vac actuator....you will need a schematic for the solenoid box harness, and check for power in the harness circuit, that corresponds to heater, vent, bi-level, etc.......Since you have a vac source, if the harness voltages check out, you need a vac solenoid box....if they don't, you need a control head....

I can't remember if the solenoid box is separate or part of a whole "programmer".....

By control head you mean the primary controls onthe dash, with temp, airflow and vent controls, correct?

I'm not sure if this helps, but here'* a picture of what I describe as the 'vacuum valve solenoid'. This is taken from under the dash on the passenger side. The black vacuum line passes through the firewall, connects to a violet vacuum line behind the glove box, then runs down and connects to a plastic piece that provides vacuum between the white nozzles. So this part has 4 valves and a 6-prong female plug.
I think the easier thing to do is just to replace the main climate controls (on the dash) and then if the problem is still there, replace the valves. Also, in that box, there'* a circuit board next to the solenoids.

Thanks!