Can any one tell me what service the pictured device preforms. The white line from the device branches through a "Y", one line disappears some place along the firewall towards the passenger side. The other into the car on the driver side of the engine compartment under the hood spring.

On an 84SD/126 Is there a vacuum reservoir some where?

There two other lines going into the car. One is brown, I believe for the engine shut off.
The other line is red with a blue stripe.

I am trying to determine if the lack of heater door activity is from no vacuum or no electrical signal from the control.
The heater works except the heat cannot be directed by the push buttons

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1984 300SD turbo 126
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I think the one that goes under the dash may be just a vent but not sure. There are servos under the dash that open and close the defrost/heating doors. They are a bear to work on. Some have single diaphragm and some have double. I seem to remember that the double diaphragm ones can be repaired; not sure. Search the forum. There are a lot of posts on these things and the diaphragms.

It is placed at about the same place on the 124 diesels as the line that runs through the ignition switch to the fuel pump shut off. Try disconnecting it and see if the car turns off with the ignition switch - if not, then you'll know.

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