I have a 1998 Ford Taurus. When I rotate the temperature dial on the instrument panel beyond the half-way point, I hear a clicking noise. This noise does not stop until I return to before the half way point. I was told by Ford it could be a blender door actuator. When I told them that air does blow through all the optional ducts when the vent dial is changed, they were puzzled. The air temperature never gets hot.
I’ve got a '97 and had the same problem. It’s a repetetive “clunking” or “flapping” noise you’re hearing, right? It IS the blend door actuator. The BDA a small, plastic, milky-white cigarette pack-sized box with a keyed plastic shaft sticking out of it that is held in with 4 (5?) screws under the center of your dashboard (behind the cigarette tray). One of the plastic gears inside has a cracked tooth, causing the slippage. I paid $42 at the dealer for a new one. Takes about 30 minutes to install (once you’ve contourted your back into position over the front seat and underneath the dash).
In the meantime (I actually did this for two full seasons before replacing the broken BDA), you can get underneath the dash and push that silver, slotted, popsicle-stick-like bar (that moves when you turn the knob on the dash) to the desired position (UP or Down for full heat or full cool), then fix it in place with something. I jammed a piece of cut plastic into the slotted hole to keep it propped up (I think it was) for heat. Tried twist-ties first, but that didn’t work for me…
Exactly right, it’s a broken blend door.
The controls for defrost floor etc are a seperate thing alltogether.
Thanks for the info.