CSS disconnected

[wwheeler]

I am trying to find information for friend with a W113 (auto and a/c) but do not remember the model or year. He says that his CSS is not connected and in fact there are no wires from the harness for this. I recall reading in this forum some years back some cars left the factory with a CSS but was not wired to operate. I tried to find using the search, but to no avail. I can get the year and model if needed. Did I just imagine this? 

Thanks for the help.

[lpeterssen]

Dear wwheeler

You have to look at the Mercedes automatic transmission wiring scheme.

See photos uploaded on this link:

https://www.icloud.com/sharedalbum/#B0QG0ehgLzrWBZ

The file attached is the most important to understand how to connect the CSS (constant speed selenoid). It is on the photo the part shown as number “53”.   The CSS receives a positive feed from fuse no.5 with a cable in black/green/red.  The trigger for the CSS comes from the pressure valve on the automatic transmission.  That trigger signal is NEGATIVE and is the cable green/red.

If an air conditioner system is added the following has to be done:

1. Activation signal from any A/C system is normally taken in parallel to the signal used to engage the compressor. That signal is POSITIVE.  The signal of course should be taken after the BINARY SWITCH which checks if there is enough refrigerant pressure in the system.
2. As trigger signal is POSITIVE and the CSS already is constantly fed with a POSITIVE cable from fuse no.3, the polarity of this trigger signal has to be changed to a ground signal by using a simple RELAY.
3. connection on this RELAY will be:
    3.1.  Port 85 connected to ground
    3.2.  Port 86, use the trigger signal coming from A/C compressor
    3.3.  Port 30, connect to ground
    3.4.  Port 87, connect to the negative terminal of the CSS in parallel with the signal coming from gear box
                         Cable Green/red.

Another level of sophistication can be added to this layout by considering the signal of the IDDLE SWITCH on the intake manifold so that ONLY if car is IDDLING (IDDLING switch clossed) will be needed any RPM correction (increase) by the CSS if A/C compressor engages.

PM me for further details on it.

Here some A/C subwiring harness I have made for some other happy customers.

https://www.icloud.com/sharedalbum/#B0Q52plgjSkXR7

Best Regards
Leonardo Peterssen

[mrfatboy]

You did not image this. Some cars did leave the factory with a CSS but not hooked up.

I know that JonB’s  sept? 1969 280sl Auto has the css but not hooked up. I don’t think he has AC and that might be the distinction.

Im sure someone can confirm.

[Pawel66]

We talked about this, yes.

The function of idle control in late US cars was taken by the Emission Control System. CSS was then left there for AC, but if the car had no AC (often or always installed at dealerships), then CSS was just left there.

I think the post above by Ipeterssen on hooking AC to CSS is important - I remember this has been asked a lot of times on the forum by Members.

[ja17]

Some USA cars without AC, did not have the solenoid connected from the factory even with automatic transmission. Normally the USA cars with AC and automatic had the solenoid connected. The vacuum dashpot and slip-linkage rod was used to maintain constant idle speed on latter USA 280SLs with automatic transmissions and if the car did not have AC (as is John B.), then the CSS was in place but never connected.

[Jonny B]

I will confirm, 1970 280 SL, with a Sept 1969 build date, automatic transmission with no A/C. It does have the CSS and it is on the engine, but there is no wiring/connection.

My installed spare for the 250 SL