You NEED to remove the center console. It's very easy. Once removed, then remove the computer. Where the computer is located is where you want to make the cut in the airbox. Just make it big enough so that you can get the broken flap out. My cut was about 4"W x 3"H. Don't cut all the way to the edges or you won't have anywhere to drill the support brackets to. Don't worry about making a perfect straight cut because you'll use the piece you cut out for the patch job and it will fit perfectly no matter how good the cut.

 

Age is most likely the cause of flaps breaking. They get brittle after a while. For the price of the flap, I would just get a new one vs drilling. A new one will probably last you the life of the truck without any modifications to it.

 

I just did this today, maybe a couple hours taking my time, pull the kick panels down and remove the center console, you need a 7mm and a 10mm for this part, then behind the console is a small computer, unplug and and its just snapped into a bracket, pop it out, here you will need a 5 or 5.5mm socket to remove the computer bracket. once thats out of the way cut your hole just dont go all the way up along the seam of the box so that you have something to put a couple screws in, reach in and pull the broken door out, its the one in the back, not the one above, you may have to push that up to get to the back but be gentle, next remove the actuator and the arm from the end of the flap from the outside and then pull that remaining peice of shaft out from inside the box, the door goes back in actuator end first, then the other end just pops in, the door should move pretty smoothly and stay in place, i cut a small strip of tin from a refrigerant can and put 2 screws in it to make a little strap to hold my access flap in place while i goobered it with silicone. By the way i used a die grinder with a regular metal cutoff wheel to make the cuts, my carpet is charcoal colored so it didnt make a mess that i can see but if you have a lighter color you make want to lay and old sheet down in there.

I hope this helps someone.

I will try to get pictures up.

i wonder how much this costs to actually have fixed at a shop. It took me a couple hours and a $20 dollar part

 

I gave up with this issue long ago. My actuator gate and vacuum motor was/is working fine as I had cut a big enough hole in the plenum to get my hand imside and feel things moving when I hit the controls with the other hand. I could see nothing wrong inside either!
It is beyond me why I have no floor heat!
I decided to replace the plastic strip I had cut from the plenum(front) and plug the hole as, in summer, a hole below will subtract from cool air on the dash vents where you need it when the air conditioning is on.
In winter it is more important to have defrost than floor heat.
"Saftey first", I say!
I have devised a way to control floor heat manually with a new round hole I cut at the bottom facing my feet. A tapered rubber bathtub style plug now hangs from a chain which I pop in or out as needed while not using the floor heat setting any more, at all.
This way I still have adequate defrost which I will rob air from as the winshield clears and as my feet get cold. This works for me and I live in Canada, land of extreme temperatures!

When this gas pig finally dies I will not be replacing it.
I'm all done with GM products!

 

Okay Mr Juicer,

I supposed you have already come up with a solution but if not, I have just found the answer. Remember that this post originated with me in the first place. I have been without defrost ever since, because I cut a hole below and never plugged it. The forum didn't help me much excepting that I discovered where and how big to cut this access hole.
Now I know, however!
My last reply to your question was lame as I had not built up the courage to fully tackle the issue. I was more intent on a hare brain solution then.
Today I discovered my broken door diverter(broken plastic axle), a second door tucked up away from the larger first diverter gate that was working okay. Just stick your hand in a bit further, start the engine and run the controls with the other hand.
The smaller diverter gate controls floor heat and the axle end potrudes out the plenum right at the lowest vacuum actuator on drivers side. A seperate white plastic piece hooked to the vacuum motor(outside) slips over the diverter axle end and, once removed, allows the broken axle remnant to be pulled out from the inside.
If you or anyone needs photos, I have them but am not sure how to include them in a blog. Just send me your Email, if you like.

 

Glad you got it fixed, i have some pictures too but cant upload from my phone, i will put them up if i ever think about it sometime when im actually at a computer.

 

My heat stopped working too. I saw the shaft rotating but the damper is not moving. I just put a clothes hanger up the duct to hold it open, only problem, the defroster doesn't work so well then.

Anyone connect a manual damper control?

Thanks

 

No, a manual damper control is not the answer. This is a safety issue as you do need defrost! Your shaft is broken like mine was. I think what happens is the heat over time warps the plastic damper shaft inside the plenum. Now it is bowed instead of being straight. Then the shaft is prone to jam and the vacuum pod/motor actuator has tons of power. The result is the shaft snaps into two pieces when it jams. You need to cut a sizeable hole in the front of the plenum and remove the entire damper. A bunch of crap has to be removed first, including a module containing two plugs and multiple wires. Remove it and cut your hole. Remove the actuator motor, prying it towards you. No need to remove any vacuum lines from this motor. The drive end of the damper shaft is rectangular to accomodate a levered drive link piece. This piece contains a torsion spring. Getting this white plastic lever link piece off of the drive end(broken stub) is a bit of a challenge as it has to be done where it sits. There is a small hole in the end so just insert a small screwdriver and pry up a tab as you pull towards you,.... while standing on your head. Then pull the broken stub out(drivers side) from the outside. I would recommend a new damper which you install again through the same hole you removed the broken damper. Once inside, poke it through the actuator side first and then just push it so the other end seats into an internal support boss. The drive end will be potruding out and you now re insert the white plastic link from the outside. Re attach the motor link, plug the hole in the plenum and......Bob is your uncle! You can have this all done in a shop but it will cost you a hefty sum.

 

I'm too scared to look at mine; my actuator is dangling in the floor by the accelerator pedal, and the air temperature that comes out of the vents in that mode feels hot enough to boil water

As long as it's on defrost or vent, the temp control seems to work pretty normal. I just don't want to look at it this season... I've fixed enough.

 

I have a 97 4WD and have over the years suffered problems with the heat/air vent door system. I troubleshoot by removing the pneumatic switch in the dash (next to the blower speed control) that controls the various actuators. Once you have disconnected the rubber connection to the switch, you have access to all the door actuators and can use a hand vacuum pump to see if each one will hold vacuum Use a small piece of tubing to place inside the rubber connector and draw a few inches of vacuum, be careful not to draw too much or you could damage the actuator. This should operate the actuator and hold it in place. In most cases I have seen bad actuators, unfortunately under the dash, that have leaks and will not hold in place. The typical symptom is air directed through the floor and or defrost vents, but not through the upper (face) vent. You may also notice the air flow shifts to the defroster as you are driving uphill or accellerating. Otherwise, look for leaks in vacuum lines tubing and connections that are not actuator related. But it's easy to test your actuators first using this simple method. If you have to get under the dash to replace an actuator it's a full day's work :-(