My heat and airconditioning are working fine, except that as the driver's manual says, I should be getting air from my center vents when certain buttons are pushed. It also says that cooled or heated air should be coming out of the rear vent in the console between the seats. This vent is presently only producing fresh air at this time.

I looked at a diagram of the vacuum and vapor hose system for this car. Over the summer I had an intermittant problem with not getting much cool air through the center vents in the dash. When I heard a certain flap close - all of the sudden the air flow would increase and air started blowing from the center vents in the dash. It was like in my wife's Honda accord when you put the system on recirculate you get a lot more air flow than fresh air only. I noticed in the diagram for my 1982 300sd that there is a #41 vacuum element for fresh air/recirculating air. I am wondering if this might be the problem for both the rear seat console vent and the non-existent air flow through the center vents in the dash. There is also a switchover valve #18 in the diagram for the fresh air/recirculating air flap. Could this be an issue too and where are these two items located?

Has anyone ever replaced theirs??

More than likely, like most of the rest of us, one or more of the diaphragms in the vacuum pods that actuate the flaps in the acc system are going/gone. My 1981 SD has worked flawlessly until yesterday when the footwell vacuum element failed. Since you have to tear into the dash to get at all this stuff, I'm just going to replace all the diaphragms at once. My failure has caused only cold air to blow out the rear vents, due to the nature of the design. I have studied the diagrams carefully and have determined that with the failure of my footwell flapper, the air backs up and flows out the rear vents before ever reaching the heater core.. It really is a complex system. Oh yeah, I have yet to hear of anyone replacing the switchover solenoids, the vacuum elements seem to be the weak link. Could happen though.

I have never replaced the fresh/recirc. actuator on mine. However, in order to gain access, you need to pull the glove box. The box is held in by a plastic insert "rivet" with 2 parts. Pry up the insert and once removed, the outer ring lifts out.

If you just want to verify it's operation, in the upper back of the glove box is an oblong flexible plug. When you pry this out, you can see the flap open and close for fresh/recirc. air. (A handy little port for occasional air freshener also ).

Intermittents may be in the dash climate controller unit. This is easily repaired by touching up solder connections at the edges of where the circuit boards meet. (If you are not comfortable with circuit work, bribe a friend who is. )

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Sam

84 300SD 350K+ miles ( Blue Belle )