CSS Solenoid w manual transmission

[ramcdonald]

Among many little "non-factory" issues I've discovered while tinkering under the hood of my 71 280 manual trans, I've found that the Constant Speed Solenoid (CSS) is both disconnected and apparently inoperative anyway.

I've procured a reportedly working solenoid off ebay but don't know how/where to electrically wire it up so that it does it's thing when the AC compressor kicks on.

The solenoid unit on the car has two posts on the wiring block, each of which having a wire from the post into the guts of the solenoid.  There is however, only one wire from the wiring block leaving the solenoid.  (See attached picture, if I can figure out how to do the attaching)

The CSS unit I've procured has a wire stub leaving each of the two posts.
My first question is:  Is one wire from the CSS correct for a manual car, and if so, to where should it be wired?

Second:  Can I test the "new" CSS unit by simply applying 12v to one of the wire stubs and grounding the frame?  

Third:  Is there supposed to be a bushing on the lever arm where the CSS solenoid would contact the throttle arm? (again see picture)

Its definately summer in the deep south...AC in use.

thanks,
Richard

Download Attachment: CSSsolenoidsmall.jpg
69.21 KB

[Cees Klumper]

To your first question: I would expect you need two wires, but not sure about that. Wiring to the A/C circuit somewhere?

Second question: yes, I believe you can test the solenoid by applying positive and negative leads to 12 volts

Third question: I don't think your unit is missing a bushing. It looks like a few similar ones I saw at Blacklick last weekend.

It's definitely good to have the CSS operating effectively.

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[al_lieffring]

quote:Originally posted by ramcdonald

I've procured a reportedly working solenoid off ebay but don't know how/where to electrically wire it up so that it does it's thing when the AC compressor kicks on.

The solenoid unit on the car has two posts on the wiring block, each of which having a wire from the post into the guts of the solenoid.  There is however, only one wire from the wiring block leaving the solenoid.  (See attached picture, if I can figure out how to do the attaching)

The CSS unit I've procured has a wire stub leaving each of the two posts.
My first question is:  Is one wire from the CSS correct for a manual car, and if so, to where should it be wired?

Second:  Can I test the "new" CSS unit by simply applying 12v to one of the wire stubs and grounding the frame?  

The two terminals on the solenoid are isolated from the ground so either one can be hooked to + and the other to ground, polarity doesn't matter.
Most of these solenoids are hooked up in paralell to the compressor clutch. Often there is too much load on this circuit and the idle won't bump up untill the throttle pedal is pushed, A relay added to the circuit would help get full voltage to the A/C clutch and the solenoid.

Al Lieffring
66 230Sl
Jones'n for a new gas tank

[George Des]

Richard,

I have a manual with an A/C system, but I use a rotary compressor and it hardly pulls down the engine idle so I do not have a CSS on mine--my 230Sl did not originally come with A/C though. My guess is that the CSS needs to be connected to the same line that goes to the A/C clutch since you want the CSS to activate when the clutch is engaged. The body of the CSS probaly provides the ground. Hope this helps.

George Des

[George Des]

Al,

Looks like we both got to this at the same time!

George

[jeffc280sl]

Here is a wiring diagram for a manual transmission MB.  Its from the BBB for our cars but the section refers to the S, SE and SEL models so I don't know if the SLs came this way.  The circuit is simple and will work on our cars.  My car has A/C and no fast idle solenoid.  Hummm.  The A/C is not hooked up so I can't tell you if it works okay.  One day I'll put a rotary compressor in it and not worry about the idle.

Download Attachment: ac wiring.jpg
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Jeff C.
1970 280SL 4-speed

[ramcdonald]

Thanks to all.  As soon as it cools off in my garage (probably about 6:00am), I'll get going on these suggestions.

Richard