Thread: The great blend door teardown (with pics)

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  1. #1
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    Default The great blend door teardown (with pics)

    So a week or two ago I drained my coolant and refilled it and turned the heater to full on to make sure the heater core purged any air (which I later found out was unnecessary). In doing so, I suddenly lost the ability for my HVAC system to blow cold air. I wasn't sure what was wrong initially, so I went through as much troubleshooting as I could. There is not water valve in the heater core plubming, so that ruled that possibiliy out. Turning the temp dial made noise at the servo, so it appeared to work. I later snaked a boroscope on top of the HVAC box and could just barely make out the plastic coupler that connects the servo to the blend door (seen later) and saw that it appeared to be moving. I finally put the boroscope down the dash vent and into the HVAC box and saw that the temp door wasn't moving, so it was time to dig into the dash to see what I could do.

    I have a service manual and would suggest that anyone who enjoys wrenching on their own cars gets one. It is a great piece of literature and has some very good info in it. Not only does it tell you about removal and installation for components, but a lot of the time it will tell you the method and theory of operation as well, which is fun for an engineer like myself. Reading through it, the dash had to come out to get to the HVAC box, so I got everything ready and dug in.

    I have done half of this job a few times now as I replaced all the lights in the car with LEDs I bought as a kit, so it wasn't really that bad of a job. I had the whole dash out in about 1.5 hours and pretty much the only "special" tool you need is a set of torx bits. The rest is just a phillips screwdriver and typical sockets. A trim stick can be handy too to help prevent damaging the plastics with metal tools.

    The first step is to remove the center console cover and shifter boot. It's just held in by snap clips and can be pulled straight up. Be careful to not pull too far though as you have to unplug the cigarette lighter and window switches. Next, the center instrument panel comes out which is held in by the visible allen head screws around its perimeter and the oen phillips screw at the bottom that is normally hidden by the center console trim. As a side note, strictly speaking I don't believe the seats have to come out, but it gives you so much more room that I would recommend it (which is why they aren't in any of my pictures).

    DSCN0889 2.jpg

    Next, the center tunnel needs to be slid back, though in the end it's easier to just remove it as well. There are two screws at the front that attach it to the main instrument panel trim (the big black plastic piece that goes around the steering wheel gauges), four screws under the arm rest storage compartment, and two screws at the back that attach it to the rear waterfall panel. I didn't remove it initially, but when I went to pull the dash itself out I just took it out to get it out of the way.

    Afterwards the sill plate trim pieces and kick panels can come out. The sill plate trim is just held in with clips and can be pulled straight up to remove.

    I'm talking about these panels:

    DSCN0924.jpg

    The kick panel on the driver's side has two push pin christmas tree things holding it in down by the pedals and a single phillips screw that is under the sill plate trim. The passenger side only has one push pin and the same phillips screw.

    With those out of the way the lower dash panels can come out easier. The driver's side is held in with two screws on the bottom and a few press in clips. Remove the screws and start at the outboard side pulling back towards you and down just a tad to remove the clips. Then pull sideways a bit to release the clip that holds it to the tunnel. Remember to unplug the pedal adjuster switch as well.

    You can remove the passenger side next, but it is a bit easier to remove the main instrument panel surround first. And to remove it, it helps to pull the steering column cover and lower the column. There are two screws at the front of the column cover (go in from the bottom), and the back of the shell just clips together. Pull the screws and press in on the bottom half of the shell towards the back to release the two halves. Aftwards, you should be able to see two nuts that hold the steering column up if you look down in there. Loosen these are far as you can without taking them off and it will let the steering well come down to give you more clearance to get the instrument panel surround off.

    The nuts are where the yellow arrows point.

    DSCN0922.jpg

    There are three screws that hold the instrument panel surround trim in under the driver's side lower panel that we just removed. Otherwise the rest of the panel is held in with press in clips. Be careful here and pull gentle and directly near the clips if you can as this piece is large and could crack. It's also got that soft touch finish, so you don't want to hit it on stuff on the way out.

    DSCN0891.jpg

    On the passenger side you'll need to remove the glovebox door first to remove the lower dash panel, which is three torx screws on the hinge along the bottom and the two plastic tethers that just clip out. With that out of the way there are two screws that are under the center instrument panel trim and two (I think) screws along the top edge that get removed and the panel can pull out in a similar motion to the driver's side (down first then to the side).

    DSCN0893.jpg

    As a side note here, you may notice I have tons of felt patches on my car that you will likely not have on yours. I have been dealing with a bunch of squeaks and rattles in the past and tried to quiet them down by felting where panels attached. So far it seems to have worked reasonably well.

    With all the panels removed, the last piece to come out before the dash itself is the steering column. The Viper has a neat feature here. The column actually has a joint inside the car, so you don't have to remove anything from the engine bay (which can be hard to get to). Before removing anything though, you'll need to unplug the 5 connectors that go to the steering column. After that, go under the dash to find a u-joint with a pinch bolt. Remove the pinch bolt and the two nuts at the back of the column, then finish removing the two nuts that we loosened earlier to lower the steering wheel. You may have to get a screwdriver in the gap of the u-joint to spread it a tad, but the column should just pull back and out once you've lowered it enough to clear the front studs.

    DSCN0897.jpg

    Okay, now that your car is looking a little more barren, it's time for the big daddy, the dash itself. First things first, we need to disconnect all the electrical connectors and ground wires. On the driver's side, up under the kick panel is the BCM. It has 5 connectors on it that need to come off. There are also two connectors that go to the door as well as a large connector with a latch style lock and one more larger connector. There are also two ground wires on a single bolt on the outboard side, and two more on the inboard side on individual studs. The two large connectors are mounted on tabs that you'll need to remove them from. The white connector pulls down (I think) and the black connector pulls back I believe. You also need to unplug the pedal adjust motor and the brake switch, which are easily visible from looking down the hole where the steering column used to be.

    DSCN0913.jpg

    DSCN0912.jpg

    To be continued on next post (due to picture limitation).
    Last edited by MoparMap; 09-06-2017 at 11:50 AM.

  2. #2
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    Default Re: The great blend door teardown (with pics)

    While we're still on the driver side, there is a brace to remove. It's held in by a nut at the top and a screw at the bottom (next to the ground wires that need to come off).

    DSCN0916.jpg

    DSCN0917.jpg

    Over on the passenger side there is another handful of connectors to unplug. The same two door connectors are tucked up next to the dash pretty good and can be tricky to get to. Otherwise there are the two HVAC connectors for the blower motor and blower motor resistor (these might be able to stay plugged in, but I unplugged them to be safe), as well as another large latch style connector or two. You may have to peel back the carpet a bit to get a better look. Again, the large latch connector is on a clip that you'll need to remove it from by pulling down (I think). There are also a pair of ground wires on a single bolt that have to come out.

    DSCN0910.jpg

    With everything unplugged, now we get to the dash hardware itself. On the inside there are two bolts per side that have to come out.

    DSCN0914.jpg

    DSCN0915.jpg

    DSCN0918.jpg

    DSCN0919.jpg

    After these, we have to go under the hood for a few things. First, remove the wiper blades by taking off the rubber pivot caps and removing the nuts. Next, the wiper cowl cover needs to come off. This is a two part piece and is held on with torx screws and two tricky bolts that are a bit hidden. On either side of the car in the upper door hinge area there is a small bolt that needs to be removed to release the wiper cowl.

    DSCN0895.jpg

    The passenger side comes off first and is a smaller piece (coincidentally also the exterior air intake for the HVAC system). The driver's side comes off next (be sure to disconnect the washer hose at the tee too).

    After that the HVAC intake plenum comes off. It's held in by two screws at the back by the fire wall and two up front just behind the coolant reservoir. To remove it, you pull it towards the engine a bit and forward. It's a bit wedged in there, but it'll come out.

    Afterward, the wiper assembly comes out. It's held in by two bolts and a nut. Be sure to disconnect the ground wire and the electrical connector as well. Sorry I don't have pictures here, I was in a hurry to finish up disassembly before dinner that day. As a side note, with the wipers removed there is a ton of access to the back of the engine for work like replacing spark plug wires, removing valve covers, or even bellhousing bolts. I was rather surprised.

    Lastly, the final thing holding the dash in are 10 nuts on the firewall. There are 2 hidden nuts on either side that are in little pockets, the rest are pretty easy to spot.

    DSCN0900.jpg

    DSCN0901.jpg

    Next up, the HVAC box...
    Last edited by MoparMap; 09-06-2017 at 10:19 AM.

  3. #3
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    Default Re: The great blend door teardown (with pics)

    With the dash hardware all removed, the dash can come out. It helps to remove the rear view mirror at this point too as you can use the extra space. It's a single torx screw and two connectors.

    You will need an extra hand here as well. The dash is pretty heavy and awkward to move around. It basically pulls straight back, but you will hit the center portion of the dash on the shifter and emergency brake. You have to do some wiggling and twisting and maybe some very light bending of plastic to get it to clear. I'm not really sure what else to suggest shy of removing the shifter, which I didn't feel like doing at the time. There are also two more connectors to unplug on your way out on the airbag module (two big yellow plugs).

    Naked for all the world to see:

    DSCN0902.jpg

    Now I can finally see the HVAC box it all its glory.

    DSCN0903.jpg

    Naturally, the servo I'm concerned with is the only one you can't take off with the box still mounted in the car, lucky me. However, if you loosen the box (one bolt on the firewall, two nuts on the engine bay side near the A/C lines, and one nut on the interior) you can pull it back an inch or two and rotate it down a bit. With some clever work using a wrench and a screwdriver bit I managed to get the servo out.

    The offending servo:

    DSCN0904.jpg

    With it removed, I found out the stub of the blend door shaft that sticks through the box and engages the servo had sheared off. Looks like the servo got out of calibration or something too as there was a rib built into the top of the HVAC housing that was supposed to be a stop that had bent from being hit too hard. For the time being, I just drilled through the broken piece of the shaft and down into the shaft in the HVAC box and put some expoxy and a screw through them to hold them together for now. In the long run I think I'm going to have to do this project again and replace the door, but with VOI coming up next week I figured this would at least give me A/C for the trip so I could worry about it later.

    I also found out that the Safelite techs that replaced my glass a few years ago got a little carried away with some adhesive. All of that shiny stuff on my firewall and HVAC box is goo that had run down the inside of the firewall and was starting to get on stuff. Luckily I don't think it caused any damage. I wiped as much up as I could with some adhesive remover before reassembling things.

    All told it really wasn't that bad of a job. It really doesn't require any special tools, though the next time I do it I will have to drain the coolant some and purge the A/C system so I can fully remove the HVAC housing from the car. It sucks, but it is what it is.

    With the blend door addressed, the car can go back together in the reverse order. However, before doing that, I put new foam tape on the HVAC outlets as the old stuff pretty much crumbled into gummy dust.

    DSCN0906.jpg

    Dash reinstalled after playing tetris with it to get it past the shifter:

    DSCN0909.jpg

    Lower panels back on:

    DSCN0923.jpg

    Good as new! At least as new as 110,000 miles can get you.

    DSCN0925.jpg

  4. #4
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    Default Re: The great blend door teardown (with pics)

    Nice write up. This should make someone's life a lot easier down the road.

  5. #5
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    Default Re: The great blend door teardown (with pics)

    ​Outstanding!!!
    “Success is not final, failure is not fatal: it is the courage to continue that counts.”
    ― Winston Churchill

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