After Action report: Whale Blend Door Actuator Replacement
Vehicle: 1999 Mercury Grand Marquis LS with EATC

First, I'll try answering a question from up above:

This is pretty easy to figure out if you know a little about how feedback systems work. The very first thing the EATC unit has to do when you turn it on is select full cold and full hot so that it can figure out what the range of answers from the position potentiometer is for your particular blend door actuator and blend door. I'm guessing it does this by checking when the motor stalls (there are no limit switches in the actuator that I noticed), which may be why so many of them fail with crunched gears. It's pretty easy to tell that the blend door is pretty much constantly in motion on an EATC car as the computer notices changes in light (sun heating load), changes in exterior temperature, and changes in interior temperature. The exception case is min and max temperature setting, which (software) forces the door fully one way or the other.

Now onto the report:
The information on the easy/quick and dirty way to swap out the CV/GM Blend Door Actuator (BDA) is spread around among several threads here on CVN. Note that Town Cars with dual zone air seem to be completely different. I'll try to get it into a coherent narrative here:

1. Diagnostics

a. If you have EATC, run an EATC self-test. If you get some combination of codes 024 and 025 after a reset, congratulations, you've got a dead or dying BDA.
b. Manual HVAC is pretty simple to diagnose - either cranking the temperature knob changes the temperature of the air coming out or it doesn't. You can do some simple tests to make sure the problem is not the potentiometer behind the knob. Usually, it's the BDA.

2. Assume your BDA is unrepairable and buy a new one. If it turns out to be repairable, you can fix it and have a spare. You don't want to do this job any more often than you have to. I'll include some detail on diagnosis and repair later. There's some debate here over whether the Ford or Dorman BDA's are better. There are also Standard BDAs at Rock Auto, of which I know nothing. I went ahead and got a Ford BDA ($44 from Rock Auto).

3. Small Hands! The smaller, within limits, the better. If you can palm a basketball, bribe a friend who can't to do this job for you.

3. Tools. You'll need the usual basic hand tools for working on the dash to get to where you can see/touch the BDA. I used 7mm and 8mm(5/16") 1/4 drive sockets with a generic ratchet handle for everything but one screw. There's a hidden weirdo screw on the firewall side of the pass side dash vent duct that takes something tiny like a 5mm, but the same 1/4 drive ratchet kit with one 3" extension will get all the preliminaries out of the way.

Once you have gotten everything out of the way you will need a 5/16" or 8mm ratchet-head hand wrench. I used the one from Harbor Freight 96654, which did fine. The finer the ratchet teeth, the better. It's theoretically better to use a shorty 1/4" drive socket and a thin socket wrench, but the height stack has to be just right to get the handle over the BDA box instead of bumping into it or something above it. If I had a garage full of panthers to do this on, I'd grind down a socket to just the right height. You'll also need something like a large screwdriver to stick between the BDA and the plenum to pry it up and break the two firewall-side mounting tabs. I used the handle end of a 1/2" drive ratchet handle I had nearby.

I also used a pair of electrician's pliers to cut the end off of the forward two mounting tabs on the new BDA. Diagonal cutting pliers or wire cutters would also work.

4. Procedure:
a) Disconnect battery negative cable and turn on headlights. You can turn them off after a minute or so. This is to discharge the air bag capacitor.

b) Remove the glovebox. Three screws underneath through the hinge. Beware the air damper lanyard if so equipped - it's fragile and hard to unhook without breaking it.

c) Remove the dash center trim panel (with clock or trunk release in it). It just pries off - no tools required. Don't forget to disconnect the wire before you pull on the center too hard.

d) Remove the four screws holding passenger air bag in. Two facing you normally hidden by the center trim panel. Two screws facing up going in from above the glovebox through the dash reinforcement rail.

e) remove the airbag (it's surprisingly heavy) and carefully disconnect the connector. This sucker is both expensive and dangerous around electricity, so don't mess with it until you've done step a) above and had a couple of minutes wait before disconnecting it.

f) remove the right dash vent register. One screw in the center trim panel area. It snaps in, too, so a bit of prying or pulling is required.

g) Remove the right register duct. Two horizontal screws facing aft to the top and bottom of the duct behind where the right register mounted and one oddball (5mm?) screwed into the connection between the center register plenum and the duct, also horizontal and facing aft. You can't see any of these, but you can feel them and can get the 1/4 drive ratchet on them pretty easily.

Removing the duct involves pushing it as far right as possible and then shoving/prying/bending it over the plenum connection to pop it off. The warmer the day the better for this job, as it makes the plastic more pliable. An alternate technique might be to cut it through the middle and remove in two parts, then tape back together with bodywork tape during installation.

h) Remove the BDA connector and screws. Look at the new BDA and orient it the same way as what you now see on top of the HVAC plenum. I just sat mine down on the transmission hump so that I could look at it when I was trying to figure out where this or that screw was, because you really can't see very much.

Disconnect the connector. I also disconnected the two connectors to the RAS/EVO module and tucked them all out of the way. The 'mini dryer hose' going from dash to blower on EATC cars can also be tucked out of the way to make access a little easier.

You can get at one BDA screw (the one you can see) with the socket and ratchet handle or the ratchet wrench. The other one you must unscrew is on the same (aft) side behind the center register plenum and below the defroster plenum. The ratchet wrench was the only tool I had that fit in the space with the spanner end pointing right. I got about three clicks of motion per stroke and it wanted to pop off the screw head because the foam seal between the center register plenum and the HVAC plenum kept pushing it up. The solution was to put my right index finger over the screw head and wrench to hold it on and work the wrench with my left hand reaching up through the glovebox hole. It's slow, but it will come out.

The biggest impediment to using a better tool on the left-rear screw is the over-long mounting tab for the defrost plenum. I tried to think of a way to remove the extra 1/2" or so that sticks down, but found it easier to work around it instead. If you are pulling your dash for some other reason (heater or evap core replacement) you should definitely cut off the extra length of this mounting tab while it's out to make future BDA replacements easier.

You can try to get one or the other forward screws out, but I didn't have a tool combination that fit in between the firewall/firewall insulation and the top of the BDA. Luckily, you don't have to:

i) Commit violence against the dead BDA. Stick a prying tool in between the BDA and the HVAC plenum and pry it up to make it pivot about the forward two mounting tabs. It will for a bit, and then the tabs will break. Don't worry about breaking the mounting points on the plenum instead - they're much stouter than the BDA tabs. Once the tabs break they might hang on for a bit. Wiggle and pull and you'll break it loose. Remove.

j) Check the blend door arm (that 1" horizontal steel arm sticking out of the plenum) for free motion. It should flap very easily, and you should hear/feel the damped thump of the door closing against its foam seals at the travel limits. If the blend door doesn't move easily or doesn't seem to be attached to the shaft, you get to remove the dash to fix this problem.

k) Now stick your ratchet wrench in there and remove both forward BDA screws to get the broken-off tabs off of them. Put the forward screws back in with slightly more than a tab thickness of clearance between the head and the tower on the plenum.

l) Cut off the end of the two forward mounting tabs on the new BDA so that they look like a two-prong fork instead of a loop.

m) Slide the new BDA into place under the two forward mounting screw heads. You will have to hold the blend door arm in the right position to engage the BDA arm as you wiggle and settle the BDA into its new home.

n) Screw in the easy screw. Screw in the difficult screw. Make your best effort on the two impossible screws (they shouldn't need much tightening if you guessed right on clearance when putting them in).

o) As the bad manuals say, 'Assembly is the reverse of the removal operation.' I found a putty knife helpful in getting the duct to slide back over the center register plenum, but a big screwdriver works too. Don't forget any connectors. If you're worried that the BDA was not the problem, it's completely OK to hook the battery up and start the car with the duct, airbag, and glovebox missing and watch the BDA arm rotate as you play with the dash controls. Yes, the airbag light will stay on. Just remember to go back through the battery connection safing operation (step a) before hooking the airbag up.

My total elapsed time was about two hours, but I made several trips back to the shop for more tools, and I was definitely not hurrying through the procedure.

I would absolutely not pull the dash for this job unless I needed to do something else that required it - the extra time alone is sufficient reason not to do this procedure the Ford way.

Dead BDA diagnostics and repair:

The BDA just snaps apart once you get enough of those little tabs pried away from their hooks. Once you take the cover off, you're likely to see one of two scenarios (that I know of, anyway):

1. The gears are stripped. This is the more common failure reported. This could be due to a) the blend door being hard to move, b) insufficient lubrication of the gears, c) a failing position potentiometer (those black traces on the circuit board under the BDA actuator arm), or d) just plain old wear. If this is the case, the motor is probably fine, the circuit board is suspect, and you might be able to salvage some gears.

2. There's nothing obvously wrong. I had this one. I also had a flaky BDA failure for a while - it would work normally when the dash was cool, but would quit (and EATC would throw a BDA code) when the dash got hot, as from sitting out in the sun. Once it had thrown a code, EATC wouldn't try to operate it again until a self-test and reset had been done. It gradually got worse over about a month until it just quit working. The failure was due to a fractured solder joint on one or more of the connector pins caused by thermal cycling and possibly a cold solder joint to begin with. Interestingly, the blower speed control module/resistor on this car had failed for exactly the same reason three years before. This module, obviously, just needs the solder joints reheated and can then sit on the shelf waiting for the day when the new one dies. I would probably use the case and arm from the new module (because I won't need to break the forward mounting tabs to remove it) and the board, motor, and gears from the repaired module in that case.

One can also postulate a 'nothing obviously wrong' case where the motor dies or some active or passive component on the circuit board dies, but I haven't heard either of those reported.