I've been diagnosing the usual climate control problems. Got the 'no heat to the footwell' problem solved by replacing the small rubber hose that connects the plastic line to the actuator. By the way, the actuator for the footwell vents is just to the right of the accelerator. Remove the cover under the steering wheel area and it is readily accessible.
I do have a funny problem with the center vents. No air coming out, door obviously not opening. Pulled a vacuum on the line and it holds vacuum but the door does not open. I can reach up and move the door somewhat with my hand but the actuator wont move it. There are two lines going to that actuator that join in a Y right before the actuator. I'm pulling the vacuum on the line that comes off the switchover valve. Does anyone have any idea why the actuator would hold vacuum but not move the door?

Hour later---I found the problem. Someone had inserted a BB in the line to the center vents!!!! Never underestimate the creativity of mechanics! When I removed it, the line would not hold a vacuum. Previous mechanic probably thought it was the actuator leaking and plugged the line. In fact, the leak was at the three way rubber connector that joins the two lines just before the actuator. Replaced it and now I can pull a vacuum and open the center vents with a Mighty Vac.
HOWEVER, when I turn on the AC, the center vents will not open!! If I give the actuator a litle help with my hand it will open and stay open until I shut it off. My hypothesis is that the switchover valve is not working correctly and not permitting enough vacuum in that line to operate the actuator. Does this seem like a reasonable analysis? Do switchover valves fail in this manner? If not, anybody got any other ideas before I reassemble the whole thing and put off fixing the center vents until next summer?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13