Transmission Pressure Switches, CSS and AC Operation 280SL/8 emissions control

[Nicolas Aristodemou]

I am in a little bit of confused as to the wiring and function of the pressure switches the CSS and the AC activation on my 1970 US spec 280SL with emissions control. There is conflicting information in the technical manual and in the various forum posts which I suppose is applicable to various W113 models different from mine.

As far as I understand the two transmission pressure switches should be connected to each other and then to pin 1 of the relay box. Is that correct? Is that the only connection of these switches? Not connected to the CSS? In my car the CSS, although the car had AC was not not connected at all. Maybe disconnected by previous owners? I have read in the linkage tour of the technical manual that it was normal for the CSS not to be connected for post 1970 cars unless they had AC. Mine has AC but CSS is not connected. Would I be correct to connect the AC compressor activation to the CSS so that upon energisation of the compressor the CSS would also be activated? but this would have to happen only when the car is at idle. Is that taken into account by the relay box/speed relay of the emissions control system?

Thanks for any info that  might solve this puzzle for me.

[teahead]

My 1970 USA Auto w/AC does not have CSS connected at all either.

AC on doesn't seem to dip the idle much at all.  Unlike the Auto going in 4 or R.

Only thing raising the idle is the dashpot thingy on the tb.

[ja17]

naristodemou, does your engine have the vacuum dashpot on the intake linkage ?

[Nicolas Aristodemou]

Yes my car has a vacuum dashpot under the throttle body. I believe it is correctly adjusted too.... I don't seem any problems with my idle dropping and the car switching off when in gear at idle or when both in gear and the AC is operational.

I am just curious to know if the CSS should be wired as for example in the earlier 230SL cars (i.e. power from fuse box and ground from auto gearbox pressure switches, or that these 2 switches are just wired in parallel and just to position 1 of the relay box (as shown on the emissions control logic diagram found in the electrical section of the Technical Manual).

I have re-commissioned my emissions control system and seems to work fine at the moment. The CSS wiring is the last part of the puzzle, especially in view of the fact that the excellent article on throttle linkage setup suggests it should be used in my car.....(1970 with AC).

[jeffc280sl]

this wiring diagram from the BBB indicates the pressure switches are wired to pin 1 of the relay box.  i have internal wiring details about how the relay box is wired.  other than understanding the speed relay function i dont understand the internals of this module.

[teahead]

If everything is working fine (like my car now), then I wouldn't worry about that CSS thing. 

Just there for decoration.