I'm not going to waste time rewriting the original instruction because they could not be better written, so I have added images to help those that are on the fence doing this simple job.
I know others have revived their EATCs by swapping in the vacuum solenoid assembly from other Ford products, but I decided to dig a bit deeper. The problem was an o-ring inside one of the EATC solenoids. Total cost to fix the problem- 'Bout 25 cents, and a couple hours of my time.
Replacing the o-rings requires disassembly of the solenoids, but that's really not that hard to do, if one has reasonably good mechanical aptitude. But first, make sure they hold vacuum when not energized. Connect a hose to the center vacuum port (where the black tube was connected) and suck it.
It should hold vacuum. If it doesn't, the following fix probably isn't for you.
Start by removing the housing around the Radio/Climate Control by pulling on the two AC vents. It will come off fairly easy as it is only held by pressure clips. There are four T-20 screws holding the EATC module in place. Once they are removed you will need to wiggle the module out of the hole and past the clips for the housing.
The hose assembly is held in place with two 10mm speed nuts. On mine the top middle port did not have a hose connected but I guess this is normal.
The solenoid assembly comes off the EATC module by unscrewing the two T-20 Torx screws on the back side of the module.
Pivot the rear of the assembly up, and disengage the tabs at the front of
the module. Disconnect the solenoid connector.
Lay the solenoid assembly on it's back, and remove the 10 screws holding the solenoids and plenum strap to the plastic frame. At the wiring end of each solenoid, you'll see two metal tabs folded over, that hold the solenoid coil and armature to the solenoid frame.
Straighten these tabs and then carefully pull out the armature, while watching you don't lose the spring or plunger that are inside. Note the o-ring on the armature. That's what we're after.
Next, slide the coil off the end of the plenum tube, and then pinch the ends of the solenoid frame together to release it from the plenum. Once the solenoid is all apart, fit the armature back into the end of the plenum tube to check that the o-ring has a good snug fit. If it does, clean the inside of
the tube, and reassemble the solenoid. You can replace the o-ring if you like, but if it fits well, there's no need.
Make sure you pay attention to the screw flanges on the solenoid frame. Pinch the end of the frame together to fit it back onto the plenum. The spacer that goes at the plenum end of the solenoid has the inside diameter undercut, and four grooves. The undercut end goes toward the plenum, and
you'll see four ribs at the base of the plenum tube that mate with the four grooves in the spacer.
The armature slides back on next, followed by the plunger, and then the spring. (The flat end of the plunger goes into the hole first, if you missed how it came out.) Use a bit of dielectric grease on the o-ring, (I used Nylog) but do not use any oil or anything on the plunger. Make sure the tip of the
armature where the plunger seals against it, is clean and shiny. Don't get any dielectric grease on the tip of the armature. Clean and dry is what you want here. Slide the armature back into the end of the solenoid, and while pressing everything back together, fold the metal tabs back over.
Repeat this for each of the four solenoids. On mine, the one that was leaking was for the floor vent door (red hose).
It was obvious when I got to that one. I experienced the same thing. The seals were hard and the ones that were leaking very loose. The armature came out much easier than the others, and when I test-fitted the armature back into the plenum tube,
it was a much looser fit.
You might be tempted to only replace the O-ring on the leaking solenoid, and leave it at that. Don't. (Guilty as charged, yer honor...) Do them all the first time, or you'll be back in there again.