W124 Comfort Control/Vacuum/Current Drain

[ray_hennig]

Hello All.

I am trying to trace a current drain associated with the comfort control circuit.

If I unplug one connector from the Comfort Control Module (CCM), the current drain disappears. It’s a drop from close to 200 mA down to about 40 mA. Unplugging this connector disables the ability to open and shut windows and roof when the ignition is off and a door is open.

The question is, “What is draining the current”.

Just downstream from the CCM is a “Vacuum Valve”, part number A0008001178. This valve appears to control vacuum to the coupé’s seat backs to lock them in position when the seats are occupied. All that seams to work.

BUT, that valve gets VERY HOT, as if it’s conducting too much current. So, as you can see from the picture, I’ve unplugged it and the current drain has dropped.

So, one and all, does someone out there have intimate knowledge of these systems?

Should the valve get hot when the car is sitting doing nothing?

Is something further downstream from the valve forcing it to continue drawing current?

Or is the valve faulty?




VacuumValve_02.jpg1181x1305 742 KB


Any guidance would be most gratefully received.

Best to all.

RayH

 

[WDB124066]

Valve or Pump Ray?

Running all the time because of a vacuum leak?
Running all the time due to faulty door jam electrical switches??
I think the vacuum reservoir is inside the front right wing, maybe not holding vacuum and the pump is firing up to compensate...?

 

[WDB124066]

mityvac - Google Search

 

[grober]

Originally the seat back locking was vacuum actuated by vacuum supplied by the engine running [later perhaps from the pump itself] --- except when the doors were opened at which point the vaccum would be switched off via a solenoid valve? allowing the back to be moved. In Electrically speaking sense the central locking valves were normally given a constant 12 volt supply [ ignition on] and " activated" by being "earthed" via the central control unit. You might be able to test this at that plug. If the solenoid valve doesn't switch it may mean that is faulty or that its constantly being activated by a short to earth somewhere wiring or a switching transistor in the control unit.
BACKREST LOCKING MECHANISM MERCEDES E 320 / E36 AMG (124066)

 

[WDB124066]

With the doors open the seat back is still locked until you press the button on the seat back which releases the vacuum...

What is item 5 or 23 [the bit that isn't the elbow], I think this is what Ray has getting hot...?

 

[grober]

BACKREST LOCKING MECHANISM MERCEDES E 320 / E36 AMG (124066)
sorry wrong link now corrected
item 5
A0008001178
1
VALVE
BACKREST LOCKING MECHANISM

 

[WDB124066]

Door switches not closing properly making the system think the doors are always open...??

 

[grober]

Correct* or a wiring short to earth--- "a" will be the ignition on 12volt supply I talked about [ main control unit not involved]
http://www.w124performance.com/service/w124CD2/Program/Chassis/91-162.pdf
* altho perversely the door switches should "open" = break the earth connection---- when the doors close!

 

[WDB124066]

Door switches corrode because they get wet, and they get wet because your seals are shot Ray. I'd be getting some more if I were you...

 

[ray_hennig]

Thanks for pitching in everyone.

Firstly, yes, it is Item 5 (A0008001178) that's getting hot. I'm not 100% sure but I think we checked that the vacuum was being held on tubes that connect to it. This was when we replaced the front seats and tested things.

Funny you all mention door switches. I carefully measured them all recently and observed good open/short circuit on the meter. However, I did order a set of 4 this morning with an order for other bits.

Regarding my switches getting wet, yes, this may have happened before we solved a wretched ingress of water. But that is no more and I have even blown €500 on new seals above the windows. having said that, I've tested the switches.

Just to recap, that valve gets hot when the car is left, engine off, key out, doors locked. I'm convinced that my current drain is due to the load that's causing the heat but I have not verified that 100%.

The valve is pretty simple, its input is a single vacuum line (the green one at the top) and its outputs are two vacuum lines at the bottom. And, of course, it has a 2 pin electrical connector to supply the solenoid or whatever switches on the vacuum. So:
>> Either the valve has shorted in some way and is thus drawing more current.
>> Or it is being "held on/energised" by something that's misbehaving. Back to door switches? What else might cause the thing to energise?

Apropos of door switches, I always wonder whether they switch more forcefully and thus open/close more predictably when "pinged" by hand. As opposed to the relatively gentle action on them when the door is closed.

More testing when I have both myself and the car at home.

Best to all.

RayH

 

[grober]

This more comprehensive circuit diagram might help--- its difficult to know exactly when this dates from/to??

 

[ray_hennig]

This more comprehensive circuit diagram might help--- its difficult to know exactly when this dates from/to??

Many thanks. Will study. It does seem to bear out my understanding. Well, almost!!

R