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Old 03-06-2012, 03:12 PM
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Vacuum Line question

Ok i just figured out that the doorlock vacuum is supplied by the trunk mounted electric pump. That being said I went to refigure some of the connection blockoff's I'd made and am hoping for some advice from the forum here..

Ok so here's a picture of the connections in question. All of these were originally connected to the main line to the booster from the mechanical vacuum pump.



The large yellowish line, was connected to the white (check valve) and does not hold vac. So I plugged it. Where does t this one go to?

The gray line runs to the VCV, that works ok as I have vac to the trans and have it shifting well...so I left it.

The red line with the green stripe and the brown were originally connected via a Y-connector to the main line...show replaced with a single tube ... The red/green goes to the HVAC controls...that holds vacuum....the brown line does not hold vac..it leaks down slow, not super slow, but it's obvious there is a leak. Whats the brown line connect to?

EDIT...here's a pic of my VCV



The grey line is the vacuum feed from the main line off the pump, the black off the side of the VCV and the tan one off the back of the IP seem to route back into the cabin...do I have this configured right?

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Old 03-06-2012, 03:59 PM
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No pics showing up on my end.
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Old 03-06-2012, 04:16 PM
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The large line goes to a reservoir in the front fender, used in conjunction with the HVAC system.

The brown line is the vac supply to the ignition switch, when the key is on, it blocks vacuum from getting to the shut off actuator. When you turn the key off, it opens the loop, provides vacuum to the s. o. a., thereby shutting off the fuel supply, stopping the engine.
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Old 03-06-2012, 04:29 PM
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thanks all for the responses, I kinda answered half my question when I got to work and the car kept running after I turned the key off...so I reconfigured the lines as such here...


TooManyMBZ, where is this reservoir located and whats up with this big yellow line not holding any vac? are you sure it has to do with the HVAC? I tested the function of the CCU and all seems to be working correctly on that end.. since big yellow was creating a leak in the system I had it plugged off...so??

Also, since the ignition line is showing a SLOOOW leak...does this mean something? From what I've gathered leaks are BAD BAD BAD mm'kay!

And what do you think of my VCV set up? Yes I need to nail down, print out and paste to the inside of the hood a vac diagram!
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Old 03-07-2012, 08:41 AM
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I don't understand it either.

The epc states it concerns the HVAC, area.

The slow leak in the ignition may be that valve failing.

VCV looks good to me.
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Old 03-07-2012, 02:17 PM
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this big yellowish line in question goes to a two way splitter feeding one line into the driverside fender and the other disappears somewhere under the battery tray...

BTW is that a heated windshield I have?

took the bulkhead down and removed the reservoir...it does not leak..just takes some pumping to remove the air...

I tested the reservoir and the other line, they DO hold vac...

I replaced the splitter with a newer one reconnected both lines...

oh and I scrubbed 30 years of grime (that looked like undercoating) off the underside of drivers front corner of the car well...

Based on the IMPOSSIBLE time I had TRYING to get the ignition switch off the occupus of lines attached to it in the donor car, I REALLY cant wait for that valve to fail...(GROAN) thats one of the things I've been meaning to read up on in case I come across another W126 with a KEY in it

Thanks again for the good info and help!
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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
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1982 300D - Blue/Blue (Sold)

Last edited by SpecialDelivery; 03-07-2012 at 03:31 PM.
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Old 03-07-2012, 03:24 PM
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Glad you found 'em, forgot there were two.

Yes, that's a windshield heater.
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Old 03-07-2012, 03:58 PM
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ahh so theres another unit of same type in the passenger fender?

and thanks for the clarification on the windshield heater...

my HVAC guy tells me not to mess around cleaning an evap that is a 8 hour R/R job...plus vaccing down and recharging the system, just to do it when I do the dash ... I tend to agree...tell me ..do you think I'm wasting my money on a new evaporator and same question about the heater core?


EDIT...how are these reservoirs related to the HVAC system...as stated in the FSM... they're not connected to that system but rather based on where they are plumbed in...Between the check valve and the radiator, that they're more to do with braking in the event of vac pump failure while driving...
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1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)

Last edited by SpecialDelivery; 03-07-2012 at 04:16 PM.
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Old 03-07-2012, 04:39 PM
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Two schools of thought about replacing the evaporator, replace everything, or just what needs it, not a clear winner.

I have no idea. But, I think you're on to something about it being a reserve vac tank.
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Old 03-07-2012, 04:52 PM
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as far as the evap/heater core arguement goes, I've seen it said on the forum that "the copper tube evaps rarely go bad" and the "heater cores are steel I think and rarely go bad"

My friend Ed, 41 years in automotive HVAC says " I dont care if it's aluminum, copper, steel...moisture when it gets in the system as yours has, having a leak, makes phosphoric acid and it eats away at the evaporators, which pool oil and acid in the bottoms of them when the system is off...same thing with coolant, it gets acidic, it eats up metal...it's a 8 hour job, what is your time worth"

I think I'll just buck up (literally, we're talking almost $300 in parts for both) and do em both..

with respect to the reservoirs being reserve tanks for braking in event of a vac pump failure, if that white thing between the lines to the tanks and the brake booster is a check valve...then that all they can be as far as I can conjure...now I am curious as to why they're under HVAC in the FSM
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Old 03-07-2012, 07:19 PM
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I'm not sure, but I thought the white thing was just a distributor, the VCV should get lower inHg than the "other consumers".

German engineers have their own way of thinking!

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