Date: Fri, 12 Aug 94 10:20:13 EST
Subject: '83 A/C vs fresh air

Well, at least part of my mystery (why vacuum servo has "locked" the
fresh air flap closed) is, well, not solved, but at least understood.

The old (i.e., '83) manual heat/AC three-lever control head does in
fact have a vacuum switch embedded in it. The whole unit, viewed from
the front:

  Front, top left: Air lever for footwell control
            right: Air lever for windshield control
           bottom: AC / "off" / Heat temp control

  Inside, lower left side: A/C microswitch, engaged by temp ctl to AC
                           (two connections, three wires)
          upper left rear: A/C thermostat/clutch/gizmo (two wires plus
                           thermostatic piping connection to A/C coils)
         lower right rear: Vacuum switch with two nipples

  In addition, three wire/cable actuators, two on right and one on the
  left (I think I got that right; cable on right goes to hot water valve
  in engine compartment, the other two to control flaps on the air/vent
  main assembly -- I was ***VERY*** careful not to disturb the cables
  since I ***REALLY*** didn't want to take the control head apart to fix
  what was still working before I took it apart...).

By carefully (tortuously) insinuating a small mirror through the maze
of cables, vacuum lines, wires (did I mention the stereo I just put in?),
and whatnot, I can see that what I thought was just a random protru-
berence is in fact one of the nipples, right next to it is a small hole
with rough edges where some ****er broke the other nipple off. Rather
than "fix" the problem, some previous bozon just hooked the two vacuum
lines together (permanently "wiring" the servo "on", recirculation mode
no fresh air).

I knew there was a reason why I don't like to buy used cars from people
I don't know and trust.

Time for an electric vacuum switch...wonder where I'll find one of
those guys? Something must exist that I can finagle into the system...

$igh.

                                        -RDH

Addenda added later:

I did secure a Mercedes Air Solenoid ("valve") from my mechanic (apparently
Mercedes engine compartments are festooned with the little gadgets). I
hooked this up via a three-position toggle (ON-OFF-ON) switch so that
the air flap servo is now switch-selectable as (Auto-OFF-ON). In the
bottom position, it connects to the A/C master power (this in turn will
disengage in normal operation and open the fresh air flap, or will
engage +12 from the A/C master switch and close the fresh air flap for
normal A/C operations), and behaves just as the original manual
A/C/Heat switch would operate. In the center position, the switch
deselects and the fresh air flap will stay open for both heat and A/C
operation. In the up position, +12 is supplied always and the fresh air
flap will remain closed for both heat and A/C operation.