There are basically two systems of pneumatic central locking on Audis of the vintage that I deal with - the earlier cars are controlled by the drivers door lock, and the later ones by both front door locks. The early ones (5000/100/200 before 1984, 4000/Coupe/Quattro/80/90 before 1988) use a pump/controller unit with a three pin connector. Here is
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an electrical and pressure line schematic of the single control system: Remember that since the control switch is in the drivers door and the pump is buried up by the passenger side trunk hinge, the wires are a lot longer than this picture might make it look. Also, the pneumatic lines snake all over the car, under the carpet, and into each door (and the trunk lid) to operate the actuators. The first step in troubleshooting is to determine whether your troubles lie in the electrical or the pneumatic side of the system (or both. ). If you can hear the pump humming away when you lock and unlock the drivers door, but nothing happens to the other door locks, it is most likely related to the hoses connecting all the lock mechanisms, the pneumatic actuators in the doors, or the pump no longer creating effective pressure. If you hear no tell tale sounds, then the first place to look will be the electrical portion of the system - the switch in the drivers door actuator, the fuse and wiring, and the actual response of the pump to appropriate signals. Master Actuator: in the drivers door, below the lock knob. Most if not all type 85 systems do not run a pneumatic line to this actuator. In the diagram it is shaded light grey, since I think some of them do. I think that apart from the most cursory checking (like, is the fuse there ), you can count on opening up the drivers door and digging under the trunk liner to get to the control...
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