Courtesy of Nick93SDV

In case anyone gets here by searching for "B1340", "actuator", "glove box", etc., here is a follow-up with the steps to access the actuators on a '97 Deville. As Ranger indicated, it was "a piece of cake".

1: Decide if you are interested in the actuators for the air mix doors for the passenger's side or the driver's side. If you only need to get to the ones for the driver, it takes all of 30 seconds. Use a 7mm socket on a driver and remove the three screws holding the large cheap black plastic insulating\hush panel underneath the glovebox. The screws are along the rear (meaning towards the rear of the car) edge of the panel. Once they are out, the panel can be pulled out (the front edge is held up more or less by the carpeting). You'll see the air mix door plunger (the metal rod with threads) where it snaps into the plastic bracket on the plastic actuator arm.

2) If you need to get to the passenger actuator, you'll need to pull the glove box.
a) There is a false panel in the front (meaning towards the front of the car) of the glove box. I'd never noticed it before. The FSM says to pull out that panel (it snaps in and out of place) to unhook some sort of air bag connection that is held in place on the exterior of the box. I never found that connection but YMMV.
b) The FSM next says to snap out the panel face on the glove box that surrounds the valet and trunk switch as well as the plunger that triggers the glove box light, reach inside, push the switches out, and undo the electrical connections. The people who wrote this must have tiny fingers shaped like needle nose pliers. I say skip this entire step.
c) There are six screws that hold the glove box in place: four around the inside rim and two that go down through the floor. Remove them but don't yank out the box yet.
d) Gently pull the box out to the point where you can see the electrical connectors to the switches and the plunger. Remove those connections using a tiny screwdriver to unclip them. Mark the one for the upper switch because it looks a lot like the one for the lower switch.
e) Remove the box the rest of the way.
f) The passenger actuator will be exposed (see #1 for a description).

3) Turn the ignition switch to "on" but there isn't any need to start the car. With the A\C-heater system on Auto, use a free hand to rock the warmer-colder temp switches between 60 and 90. You should see the actuators spin counter clockwise (as if you were looking down from the top of the car) when you get to 90 and clockwise when you go down to 60. Since you are doing this at all, it is likely that one or both of them won't go from full CCW to full CW smoothly. On mine, the lower drivers arm was sticking about half way through the travel, which meant cold air when I needed a blast of heat and warm air when I needed a frigid wind on me. A gentle push on the end of the arm got it past the sticky spot and for a while, everything worked fine. Alas, it was a temporary fix.

4) The next step differentiates the actuators from the internal air mix doors as the source of the problem. Turn off the ignition and using a small screwdriver, carefully pry the threaded end of the door plungers out of the plastic snap on the end of the actuator arms. Now you can push and pull the plungers at will to see if there are any sticking points and run the actuators in free mode to see if something internal is binding through travel. When you are done, turn the ignition switch to "on", change the AC to 60, and when the actuator goes full CW (you might have to help it if it's sticking internally), push the plunger in until you get resistance and then snap the threaded end into the actuator arm end.

5) If the problem is inside the heater core (meaning there is something wrong with the air mix doors in how they are swinging), I would suggest douching the insides with some sort of lubricant. I don't think I ever saw a post that explains how to repair the air mix door other than obtaining a good condition heater core from a junk yard (the FSM didn't seem to discuss the issue either), so while the purists will gasp at the idea of spraying WD-40\Teflon\Silicone like holy water inside a system you can't see, I think it's a low risk\high benefit approach.

6) If the problem is the actuator (e.g., sticking half way through travel when you have the plunger snapped off or making a lot of noise), the repair is to simply replace the actuator. I haven't done that yet but I will as I'm about to order a replacement from Rock Auto. But according to my FSM and my eyeball inspection, it shouldn't be more than a unsnapping the air mix door plunger, undoing a couple of screws, removing the electrical connections, and pulling the actuator out. If it is any more than that, I'll post a follow-up.

7) Until your replacement actuator arrives, study the arm as it goes back and forth. You may find that it'll work just fine on the A\C side as long as you don't crank up the heater one night (or work fine as a heater as long as you don't crank up the A\C one day). Obviously, that's just a seasonal fix but it's better than nothing. If it's a problem with a sticky actuator on the drivers' side, you could leave off the hush\insulating panel under the glove box and when you notice it sticking in one direction or another, give it a gentle shove when you come to a stop light.

8) If you've yanked the glove box, you can check the operation of the passenger side comfort adjustment dial. Basically the dial on the door allows the passenger to turn the upper actuator a few degrees CCW when a little more heat (or a little less cool) is desired and a few degrees CW when a little more cooling (or a little less heat). To see this happen, you need to be somewhere in the middle of the temperature range and the little light on the dial has to be clicking on. If it's not working right, I'm not sure what you can do to fix it but it's cool watching the actuator move as you spin the comfort dial.

Hope this was helpful.