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  #1  
Old 08-06-2006, 02:45 PM
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Join Date: Mar 2005
Location: Wilmington, DE
Posts: 148
Where are vacuum controls for A/C?

87 SDL

I've only got defroster no matter what setting I have the fan on.

I'm assuming I've got a vacuum leak somewhere but can't find it. Is it in the dash? If so what's the best way to get to it? Windows, door locks, all work fine.

I see a pink vacuum boost/reducer/transducer/thingamabob when I pull the controls out of the dash does this have anything to do with it?

Thanks,
Bill

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle
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  #2  
Old 08-06-2006, 03:07 PM
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smoke gets in your eyes
 
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Location: SF Bay Area
Posts: 20,793
The ACC unit controls a bank of switching valves that direct vacuum (so to speak) to the various vent actuators. The pink think you see in the dash is one of them. I'm not sure if you can get to the bank of switching valves through the center of the dash. IIRC you have to pull the right side panel of the center console. Check that there is sufficient source vacuum. Then check that each line holds vacuum. When you apply vacuum to a line, you should hear an actuator move a flap. You'll need a system diagram because some lines interconnect. Try mb.braingears.com if you don't have a factory manual.

This could go a lot of different directions but basically potential problem areas are:

- no source vacuum, major leak in the switching valve bank

- no signal from the PBU, unusual if there's proper blower control

- ruptured acutator diaphragms, unusual that all are bad

Could be other things.

Sixto
... stay tuned
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  #3  
Old 08-06-2006, 03:13 PM
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Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Classic sign of leaking vacuum pods.

Ready to do some work?

Remove the passenger kick panel.
Remove the carpeted piece that sits alongside of the transmission tunnel. It's not easy to get it out from behind the console.......so be careful.

Now, you'll see a set of six vacuum solenoids aligned vertically next to the CCU and radio. The bracket is held by two screws. Remove the screws for better access.

The vacuum supply hose has six branches that connect to the vertical leg of each solenoid. Connect a vacuum gauge to the vacuum supply hose and confirm that you have vacuum from the engine (presumably so).

Remove each horizontal rubber hose.......one to each solenoid........and connect your Mityvac. Pump up the circuit and see if it holds vacuum. Start at the bottom (#1) and finish at the top (#6). Some will hold vacuum. Some won't.

Report back with results on which circuits hold vacuum and which don't.

BTW, the repair of this problem will take at least one week (you'll need to order parts). Don't dive into it if the vehicle must be driven tomorrow.
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  #4  
Old 08-07-2006, 12:04 PM
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Join Date: Mar 2005
Location: Wilmington, DE
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Actually it now appears that I have little to no vacuum going to it from the main line... not sure why that is, but haven't spent a lot of time to fully investigate.

At least I don't have to play around under the dash.

Probably a clogged line in the engine compartment... we'll see.

Thanks,
Bill

__________________
'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle
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