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Mystery vacuum line


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Back in the day vacuum was used to control wipers and other items.  Not so much anymore.  I'm replacing all my cameras and monitor and doing some clean up behind the dash.  I came across what appears to be a vacuum line just hanging out under the dash between the steering wheel and the windshield.  Too much "stuff" to remove to find the other end.  But I don't think Monaco used "vacuum" to control anything, or did they?  As far as I could trace the line it went from steering wheel to curbside under the dash.  This is a 2009 coach.  Could there be vacuum being used for something?  I'm not a mechanic, but I don't think a diesel engine would use vacuum for anything, especially in this day and age.  Before I go crazy trying to chase this down, does anyone know of any reason there might be a vacuum line in the dash area?  Thanks,

Woody Miller

09 Dynasty Regal IV

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Woody, your dash HVAC is controlled by vacuum lines.  Verify that all the lines going to the control panel and all the lines going to the vacuum actuated baffle doors are connected.

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OK, yes, a vacuum pump and canister on the firewall.  One small air line going to the HVAC selector switch, no other lines that I can see.  All controls for the HVAC working.  The line that I found behind the instrument cluster has some of the gray foam sealant on it about a foot from the end, guessing at some point it crossed the firewall.  The line is not long enough to reach anything that I can see.  There is no vacuum or pressure on the line with the engine on or off.  At this point since I can trace the other end of the line I'm going to give up on it.  It runs from the instrument cluster area to the right and disappears behind the cabinetry and I lose it halfway, don't see anything coming through the firewall.

Woody Miller

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Woody, a different coach but on ours the only vacuum line going out through the firewall is for air recirculation actuator, driverside of the external air intake, above the generator. You may not notice whether it works while stationary but it makes a big difference for cooling. It gets turned on with Max Air.

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Ivan, does it make sense that the line is twice the size in diameter of the single vacuum line leaving the pump on the firewall?  It does head that way from drivers side to curbside where the vacuum is located on my coach.  And the presence of that gray foam on a section of that line behind the instrument cluster.  So if it did go through the firewall it could not go far and I just don't see anything that is could reach or control.  Now, if a person was to go to the right that would make that hose a little longer to reach something in the middle of the firewall, above the gen.  ????  I was looking for something more around straight ahead of the steering wheel.  I guess I'll take another look.  But, the length of hose between the end and the foam is about a foot, a little less really, so it would have to be something mounted to the firewall.  Thought I would take a few minutes and "clean up" some of the "stuff" under the dash while I was in there installing the new cameras and monitor, boy did I open a can of worms.  Splices, black tape, ty-raps and no documentation.  Did find a constant on voltage for the monitor during my looking around.  I have no idea what it was there for, it's not a factory splice, just a wire with a fuse holder just hiding out in there with all the other "stuff".  Without documentation a ten minute job turns into a week.

Woody Miller

09 Dynasty Regal IV

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Our configuration seems quite different and years apart. I can't think of an other use for vacuum other than HVAC in our coach... I have a bank of vacuum solenoids in place of vacuum switch and these have sort of an "exhaust " port, to relieve vacuum, with a filter on them. Don't know if your oversized line could have the same relieve function...

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3 hours ago, Ray Davis said:

Could it possibly be an air line for the entry door inflatable gasket?

You mean the door seal?

14 hours ago, woodylmiller said:

Ivan, does it make sense that the line is twice the size in diameter of the single vacuum line leaving the pump on the firewall?  It does head that way from drivers side to curbside where the vacuum is located on my coach.  And the presence of that gray foam on a section of that line behind the instrument cluster.  So if it did go through the firewall it could not go far and I just don't see anything that is could reach or control.  Now, if a person was to go to the right that would make that hose a little longer to reach something in the middle of the firewall, above the gen.  ????  I was looking for something more around straight ahead of the steering wheel.  I guess I'll take another look.  But, the length of hose between the end and the foam is about a foot, a little less really, so it would have to be something mounted to the firewall.  Thought I would take a few minutes and "clean up" some of the "stuff" under the dash while I was in there installing the new cameras and monitor, boy did I open a can of worms.  Splices, black tape, ty-raps and no documentation.  Did find a constant on voltage for the monitor during my looking around.  I have no idea what it was there for, it's not a factory splice, just a wire with a fuse holder just hiding out in there with all the other "stuff".  Without documentation a ten minute job turns into a week.

Woody Miller

09 Dynasty Regal IV

Is your door seal working?

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I can see the solenoid/control for the door seal.  The hose is going in the complete opposite direction, from curbside to roadside.   The door seal supply is on the curbside part of the firewall.  Of course the door seal doesn't activate until around 5mph as I recall.  I'd have to check that next time I'm on the road, but who knows.  I can check that with a hand pump though in the meantime just to rule that out.  Been too hot here for outside work.

Woody Miller

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I don't have an air door seal so I'm speculating that the ECM signals when to send air to the seal.

Anyway, surely that would be 12v, so why couldn't you simply jump 12v to it temporarily.  That way you can visually see what it does.

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From your 2009 Dynasty Owner Manual Page 125: 

Air Seal
The entry door is equipped with a one-piece
air seal to reduce wind and road noise.
The seal automatically inflates when the
the transmission shifts into 2nd gear.
The entry door seal will inflate to
approximately 3 to 4 psi.
The pressure regulator control valve is
located behind the front cap on the curb
side of the generator.
When the transmission is placed in
neutral, the entry door seal will deflate.
CAUTION:
If the pressure regulator should require
adjustment, do not exceed 5 psi.
Damage to the seal will occur.

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