Heater Door Actuator Clip/Arm

The part I am referring to I have circled in red. It goes behind the actuator itself, and goes from one door to another. I'm sure the spring is somewhere in the car, but the clip itself seemed to hold the bar in place, and I doubt highly that I can use it without it.

If you find the spring, you should be able to find a clip at a parts store. Have you checked?

JGONZO. You can't buy that part at any Parts Store. Maybe. Maybe. Maybe at the Ford Dealer near you, but I had to go the nearest Pick N' Pull and pull a dash apart and get it myself. I now have a few, and that's for the lower clip, the one that you use a small flat screwdriver to remove, by pushing it into the cylinder and it kinda pops out. The Top one however, is unreplaceable. That little plastic "finger" that goes down over the metal bar, cannot be replaced. I have on an 02 Ford Taurus, drilled an ultra tiny hole using a micro drill into the stem dot, and placed a tiny pin to hold the bar on. I also glued a cap of epoxy onto the little plastic dot that is left, to further help hold the pin in. That has worked.

However, on my offending 98 Mercury Sable (which I still drive), I had to cut the heater box open and replaced the whole flap door with a new one, that has a metal protrusion, that facilitates the movement of the blend door. Dorman 902-223 is the part. They are a little expensive right now, as I think I paid only $45 this past summer for mine. But, cheaper than the dealer, and better than going without heat.

Note: You have to take the dash completely off, and with an oscillating tool, and a sideways cutter, cut away at the box. It will show you in the instructions how to do it, and then tape up (I used epoxy to ensure its air tight). When you go to take the dash off, TAPE the STEERING WHEEL to itself. Which means, taping the steering wheel so it can't spin on it's own. When I did this job, I let the wheel free spin, and broke the "Clock Spring", which required another trip to the junkyard and a whole lot of extra time and aggravation, as now the cruise and horn wouldn't work, and the airbag light stays on. Just be sure when you take the dash off, to unplug everything you possibly can. Including heater fan, steering wheel, dash lights, upper controls (requires a screw in the center be removed), everything you can, and the lower shifter will be in the way too. That's a lot of fun to remove, but needs to be done, or the dash gets hung up on it.

That part number should work. I have the same car as you do. You sure its not a SHO model?
Also I took my dash apart for a third time, verified every thing works, and I still get lousy heat. I also tried to clamp down on the bypass pipe, and that didn't help either. There is just something wrong with these cars that just won't allow heat to come out of the engine somehow and circulate enough to make heat into the car. I replaced all the things you did, and more (I replaced the water pump) and for whatever reason, still lousy heat.

There is one thing I haven't tried yet, and that is to flush the core again (even though I replaced it). I figure these cars are just throwing out a lot of rust, and every year you have to flush the system. I'm going to try it with air this time, as well as water, and clamp the bypass pipe when I do it. Or this guy. https://www.youtube.com/watch?v=9LSWGL3kK44

" Even the small hoses coming to/ go from the resevior were clogged."

Okay, I have not done that as of yet, so I will give that a go next. I had to replace the reservoir tank, as the old one cracked. It was just as well, as the tank was clogged at the bottom, and there was no getting it out. Main thing was, the screws holding the thing down, there was no putting them back, so I had to zip-tie it to the frame as the old bolt holders were just junk.

I did note over the winter, that the new tank, and a new radiator cap do not mirror well, so I had to include Teflon tape over the threads to keep the pressurize tank from leaking. Kind of surprised, since it appeared to be the same material as the old tank, but had to put about six revolutions of tape around to keep it from leaking out the top.