What is this Device?

[TJMart]

Can anyone identify what this device is and what is its purpose? Also instructions to test whether it is working.

Thanks!

[teahead]

Hah!  Constant Speed Solenoid.

https://www.sl113.org/wiki/Restricted/Linkage-tour#ConstantSpeedSolenoid

You have air conditioning?

I think early cars used it for auto-trans.

Then later cars, used it for AC.  Is your's hooked up to your AC compressor?  I.e. does it energize (gets 12v) when the AC kicks on?

[Pawel66]

Hah!  Constant Speed Solenoid.

https://www.sl113.org/wiki/Restricted/Linkage-tour#ConstantSpeedSolenoid

You have air conditioning?

I think early cars used it for auto-trans.

Then later cars, used it for AC.  Is your's hooked up to your AC compressor?  I.e. does it energize (gets 12v) when the AC kicks on?

Unless it is Euro car.

I see you have 1970 280sl - if it is Euro and auto transmission, it is very likely it is for keeping constant idle when gear is engaged.

On US cars with emission control - it is like teahead is saying, I think. Might also have not been hooked to anything, but yours is. So if you have a US car with AC with CSS connected, it moves the linkage a bit so that idle is stable when you switch on AC and engine gets more load. I see one connector of your CSS is grounded. Then the other must be getting + from somewhere - probably AC. It is definitely not a set up for automatic gearbox. In the set up for automatic gearbox ground is taken from hydraulic switches on the gear box, + is permenent (after ignition) from fuse 3.

How to test it? Switch on AC with engine running and see if the solenoid pin moves forward (half an inch or so, maybe less) and moves throttle linkage so that the engine idle is not slowing down when putting AC on. If the solenoid pin does not move and it is connected to AC - solenoid does not work. If it works but engine idle still slows down - it can be adjusted.

[ja17]

The CSS solenoid. Is automatically grounded from the engine. Only a positive wire is needed to activate it. Obviously the one shown has been wired in later years.

[mBdrvr]

Doesn't this also keep the idle up when the power steering is all the way left or right (locked position)?

[Pawel66]

I think there was a bit different device, hydraulic, on some early cars to do that (not sure if on W113).

[teahead]

Wouldn't grounding one of those terminals render it useless?  Maybe even short the whole thing out?

I thought one terminal was for the DRIVE solenoid on the trans, and the other was for REVERSE solenoid.

And if for AC, then only one is used.

[Pawel66]

I think grounding was meant for when there is an AC connected to it. It cannot be ground when functioning together with transmission. On transmission we have the two switches for D and R and one three-way solenoid to manage the modulator pressure. The switches provide ground when activated by gear selection.

[TJMart]

Thanks all for your advice. My 280SL is a 4 speed so the CSS is for my A/C. My A/C was working before it went into storage for 2 years but now appears no freon. I can't get any drag on the engine to see if the CSS is working. As I recall when my A/C did work the idle speed increased randomly so I assume now the CSS worked sporadically. Must get A/C to work again first. I think it is wired correctly with the compressor wire to one terminal and the other is grounded as shown in the photos. Don't know if the wires were originally red but could have been black wires and someone rewired it with red wires.

[ja17]

Paul, the only accommodation for increase idle related to the power steering is fairly rare and only used on some models. It uses a hydraulic cylinder to move the linkage. A metal fluid line from the power steering box goes to the hydraulic cylinder.

[hkollan]

This hydraulic cylinder is used on the M189 engines found in the W112 cars.
I just replaced the internal seal in the hydraulic cylinder last week on my 1964 300 SE Lang to prevent any future leaks.
The seal was surprisingly still available from the dealer.
Picture shows the hydraulic cylinder next to the idle control magnet.

Hans K

[col320ce]

Hi Hans
Do you have any more photos of this power steering linkage to the css?
Thanks!!!

[mbzse]

This hydraulic cylinder is used on the M189 engines found in the W112 cars

I also have it in my 250SE (W108) sedan which is equipped with SA for power steering.
Purpose is (was) to avoid engine stall when you turned the steering wheel towards the end stop. The end
position increases the pressure (thus resistance) for the power steering pump. An idling engine risks to cut out
(which is annoying, the car owners think  )   
The added actuating cylinder increases idle in order to avoid such a stall.
The M130 (280) engine was more powerful at idle so this actuator was dropped in 1968