Okay, the first issue here drives me NUTS:
If the center vents don't open as they should, IT DOES NOT MEAN THAT VACUUM ACTUATOR IS SHOT.
The center vents not operating generally is caused by a vacuum leak somewhere, anywhere, in the ACC system. There are other symptoms, but people (including myself) don't generally notice anything but the center vents not working.
To DIY fix this, do as advised and remove the glovebox. You can see right behind the center vents where a plastic air duct comes up and a rubber piece connects it to the actual vents. Behind there, connected to a flap in the plastic duct, is the center vent pod.
Just a note, this only applies to 123's.
It is a PITA to remove that pod, a bigger PITA to disconnect and reconnect the vacuum line to that pod, and the biggest PITA to remove the dash in order to remove that pod.
Verify that with the temperature wheel set to minimum and the ACC on (in economy or normal mode), the pod is pulling the flap open. If it isn't, you have a vacuum problem. If it is, you have the aforementioned problem of the pin.
The pin problem is easy to solve, pull off (partially if possible) the rubber duct and use a plastic zip tie or small machine screw (or basically whatever you have on hand that will stay in place) to connect the metal piece from the duct to the metal piece on the flap. It is fairly self explanatory.
If it's a vacuum problem, the fun starts.
If you don't have a mityvac, you will need one to do any vacuum troubleshooting on this car. As they are durable and quite handy, most forum members will advise you to buy one. Just make sure to get the metal one and not the plastic (hopefully another forum member will chime in here).
The company that makes them is called silverline, search for it on google if you don't know where to look.
Once you have a vacuum tester of some sort, the best way to approach this is to just do a full test of the ACC system. The way the system works is that the CCU (Climate Control Unit, AKA that thingy with the buttons you push) controls 5 switchover valves that open and close to operate the vacuum pods. When you see them, it makes a lot more sense.
The switchover valves are located behind the wood in the center console. To get at them, gently pop the wood panel off of the CCU.
I did this with a small flathead screwdriver, starting at the radio. The thing to be careful of is that you are pulling up the metal plate under the wood and not the wood itself. As my wood has started to curl up at the corners, I had to watch very carefully.
Don't bend the panel as you remove it, just be gentle and patient.
Once that's out, you see a plastic cover underneath. This is held by four screws. Remove them and gently remove the plastic cover.
Now for the upper panel (the one with the switches, one of which is for the rear dome light).
Gently push the switches out from behind. Once they are popped out of position, remove the wires from behind them (there is a plastic wiring harness that pops/slides off of the actual switch). You wil see that each switch has one or two wires on the top and/or bottom that stay with the wiring harness, but are separate. You may want to tape these to the wiring harness, as they have a habit of popping out and getting lost in the tangle back there. These oddball wires are the fiber optics that light your switches.
Once you have the switches out and separated from the wiring harnesses, pop out the wood panel. It literally pops out, the bottom comes out, and then the top. I don't remember too much about this process, just push from behind and be slow but firm.
Now that the panels are out, the switchover valves are exposed. You may have to move those wiring harnesses aside to access them (this is where those fiber optic wires have a tendency to get lost).
As you can see, there is a rubber piece above them that connects them all to the main climate control line (the green line that starts in the hood). They are allowing air to flow or blocking airflow to the lines that come out of the valves towards you, and then curve off to the sides.
These are the lines to your vacuum pods. Now comes the trouble shooting.
In order from left to right, the lines go to these pods:
1 - Defrost full
2 - footwell
3 - center vents and defrost halfway connection
4 - recirculation pod
5 - main air pod
To test a pod, simply remove the rubber connector that connects the line to the switchover valve from the switchover valve and connect it to your vacuum tester. Evacuate the line (and the pod on the end) to about 10 inches of mercury. See if it holds this vacuum.
If you have a leak, it will be very noticeable (as in you will see a noticeable drop in under 10 seconds). The one thing to be careful of is the recirculation pod. It can trick you into thinking you have a leak when you don't because it has a very thin line connecting it to the system that restricts airflow, causing it to operate very slowly. With that, see if the vacuum stops draining, as it should once the pod is fully actuated.
All these pods, except the center vent pod, are readily accessible and easy to fix. What actions you should take depend on what is leaking and what is not.
The pod itself consists of a rubber diaphragm, a connecting piece, and a plastic shell. As air is evacuated from the rubber diaphragm, it shrinks and pulls on the connecting piece, thus opening or closing whatever vent it is connected to.
With age, the rubber diaphragms weaken and crack, thus allowing air into the system and keeping all pods from actuating.
For now, just test all five lines and report back with the results. With all but number three, you know which pod to replace.
With number three, however, the vacuum line goes to the venter vent pod AND the halfway connection of the defrost pod (the defrost pod is different from the others in that it can be actuated the full way or halfway).
If you get a leak on this line, don't panic(tm), there's a good chance it's not the center vent pod at all, but the halfway defrost connection. To test this, you must remove the driver's side kick panel (I can detail that if you need it), and disconnect the line from the middle of the defrost pod. If you lie on the floor (doing the limbo through the door) looking up at the stuff above the driver's kick panel, it is directly above you. You can see the red/pink cap.
There are two lines connecting to it, one directly above you (connecting to the pink cap) and one connecting to the middle (that you need a flashlight to see). Remove the middle one and plug it with a golf tee or something that will form an airtight seal with the rubber piece.
Now that the halfway connection defrost is removed from line three, test it again. If it was leaking before and it doesn't leak now, your halfway connection is leaking, as you can easily conclude.
At some point, I should probably get pictures and do a wiki write up of this (or someone should).
I would be happy to answer any questions (even the ones you may think are stupid - I've asked my share of stupid questions in the past
).
Hope this helps.
-Andrew