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  #1  
Old 01-10-2008, 12:21 AM
bustedbenz's Avatar
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Location: Valle Crucis, NC
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Rear Heat Vent... WHY?!?

I've read enough threads on the rear vent to think I understand two things correctly.

1. By MB design, when the weather outside is 30 degrees and dictates the use of heat... the rear vent, unless closed (mine won't close completely) blows 30 degree air at my passengers.

2. By MB design, when the weather outside is 90 degrees and I am desperately trying to cool myself off before I melt, the rear vent, unless closed (Mine won't close completely) blows 90 degree air at my passengers.

I am about 90% sure those are correctly described functions for that vent, as per MB specs.

I am forced to ask.... WHY did they THINK i would even WANT such a vent in my car?

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Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL
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  #2  
Old 01-10-2008, 01:02 AM
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Quote:
Originally Posted by bustedbenz View Post
I've read enough threads on the rear vent to think I understand two things correctly.

1. By MB design, when the weather outside is 30 degrees and dictates the use of heat... the rear vent, unless closed (mine won't close completely) blows 30 degree air at my passengers.

2. By MB design, when the weather outside is 90 degrees and I am desperately trying to cool myself off before I melt, the rear vent, unless closed (Mine won't close completely) blows 90 degree air at my passengers.

I am about 90% sure those are correctly described functions for that vent, as per MB specs.

I am forced to ask.... WHY did they THINK i would even WANT such a vent in my car?
Sounds like you need to do some work on your climate control to keep
your passengers comfortable.
Or just don`t have passengers.

Your SDL, Iam assuming this is what you are discussing here, is probably
like my 84SD. there are some plastic tubes that go to the rear vent.
remove the center consol and remove the tubes that would end to the
discomfort.

The designers of the W126 (some may not even be alive today) were
most likely not thinking about someone that wasn`t even born yet,
whether they wanted vents or not.

Get ahold of a copy of the FSM for the climate control and study up
on how it all works. once in a while one comes up on E-Bay in the paper
version.

Charlie
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  #3  
Old 01-10-2008, 12:47 PM
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Location: Longmont, CO
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That's partially correct. The rear vent should blow cold air if you have the AC on. It will not blow heat though if the heat is on, just outside air.

I have no idea why they designed it that way.
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  #4  
Old 01-10-2008, 12:56 PM
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The rear vent should close all the way. It's connected to a cable that goes to a flapper under the front of the console.

The rear vent between the seats is only for fresh air, and to help with the AC. The main rear vents are under the front seats.

Working properly the climate control on a W126 is as good as any car, I beleive the air exchange rate is 3min at full blast.

If your rear passangers are not getting heat, you should check the rear vents under the seats, I'm sure they are acuated by those vacuum pods that can leak.
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  #5  
Old 01-10-2008, 01:29 PM
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I'll check next summer to see if it's getting cold air... the main problem is just that there's always a cool breeze blowing on whoever's back there. I think the heat does work under the seats, but still... I'm just bothered that my car pumps cold air through in the cold of the winter.

I enjoy the climate control other than that, I'm not as critical of it as many others... but that's the dumbest thing about it that I've found so far.
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Past cars:

1986 300SDL
1987 300SDL
1982 240D
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  #6  
Old 01-24-2008, 12:57 PM
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Quote:
Originally Posted by bustedbenz View Post
I'll check next summer to see if it's getting cold air... the main problem is just that there's always a cool breeze blowing on whoever's back there. I think the heat does work under the seats, but still... I'm just bothered that my car pumps cold air through in the cold of the winter.

I enjoy the climate control other than that, I'm not as critical of it as many others... but that's the dumbest thing about it that I've found so far.
This may be a silly suggestion, but have you closed the center vent in the back? I just leave it closed all the time. If passengers want air in the summer, they can open it. If they want heat in the winter they'll learn really quick that it's not blowing hot air.
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  #7  
Old 01-24-2008, 01:04 PM
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He already posted that his is not working correctly. It will not close completely.

I have the same problem in my S350D. Mine does not close at all. I found that if I take the vent grill loose and pull it out it shuts the flapper. Not pretty, but effective. I just got the car Saturday and have not had time to do a final fix.

-Jim
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  #8  
Old 01-24-2008, 01:10 PM
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Quote:
Originally Posted by Jadavis View Post
He already posted that his is not working correctly. It will not close completely.

-Jim
Whoops, forgot about that, or simply missed it.
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1983 300SD
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  #9  
Old 07-07-2008, 04:12 PM
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Quick question on the center rear vent... I have an 85 300SD, and that rear vent is stuck open all the time... I'd been meaning to look at this for a while, and lo and behold, someone broke into the car and stole the crappy old radio out of it a couple weeks ago (arrgh)... good news is, it did make it easy to FINALLY look at the whole center console/vent thing...

Anyway, it looks like the wire that controls the vent is hooked up in the center console -- when I move the slider in the rear vent, I can see it working in the center console... is there anything anyone can suggest that might be the issue here?
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  #10  
Old 12-30-2011, 09:20 PM
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The 300SDL rear passenger center vent is stuck in open position. It slides OK but stuck in the last inch and fails to close. What it takes to fix it?

Do I need to remove the window switches wood panel?

Thanks
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  #11  
Old 12-30-2011, 10:06 PM
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The answer is you need to take a look at the mechanism which is really simple.

1. Pull the ashtray assembly by removing the two screws under the pull out chrome ashtray. There is a bulb and an electrical connection for the cigarette lighter. Remove them.

2. Remove the coin holder underneath the ashtray assembly which is color coded to match your interior. It wiggles out. The front lip gently slides underneath the lip of the gear selector wood panel. You will want to move it backwards slightly for removal.

3. Remove the radio. My instructions only apply to OEM Becker units. Gently pull down on the two metal tabs beneath the radio assembly. It helps to slide a screwdriver under the tab and release one end of the radio before doing the other side. Remove all electrical connections from behind the radio once you've pulled it out of its holder.

4. This gives you enough room to proceed, although you may want to consider removing the ACC wood by releasing the two screws once hidden by the radio and gently sliding the wood down from the dashboard overhang. If you do this you need to unplug all the upper dash switchgear. Be careful with the fiber optic wiring going into each switch.

5. NOW you can look into the mechanism which controls the flap that controls the air to the rear vent.

a. Look down into the crevice where the coin holder once resided. Move your rear vent slider back and forth and you should see a wire that is sheathed in a plastic sleeve moving a plastic lever back and forth. You MAY need to adjust a factory installed insulation cloth that goes around the two air passages which travel to the rear vents around the gear shifter to see this mechanism in action.

b. If you want to see how it should work GENTLY pry the bicycle cable off the plastic control lever. DO NOT BREAK THE PLASTIC LEVER OR YOU WILL BE IN BAD SHAPE AS THERE IS NO WAY TO EASILY RECTIFY THAT. I recommend using a screwdriver to first loosen the bicycle binding and then use needle-nose pliers to remove it. You also need to carefully remove the metal clip which secures the plastic sleeved wire that is connected directly to the vent slider.

c. Now with your hand move the plastic control arm back and forth and you will feel it open and close the flap which seals or opens the air ducts which supply the rear vent. You can easily feel the flap move by pulling the plastic ducting off the two sleeves on the HVAC casing and sticking you hand in the holes.

d. The trick for the unit to work is making sure the plastic sleeving is secured with the metal clip such that the range of motion of the flap is appropriate.

e. If I had to guess what was wrong, I would guess that the metal clip isn't securing the plastic sleeved wire. The metal clip binds onto a plastic "lip." It's easy for the plastic lip to break after so many years. If this is the case, the wire will "flop around" and not properly move the plastic control lever for the vent flap. To fix this, bend the metal clip or fabricate one such that it secures the wire to the "lip."

Good luck.
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  #12  
Old 12-30-2011, 10:57 PM
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in my 82 SD, the center vents do indeed blow A/C cooled air. they do not blow heated air.
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  #13  
Old 12-31-2011, 12:36 AM
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I don't think there's any denying it... even on a peach - by the time we get our hands on these cars, the whole climate control system is one big huge mess.
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  #14  
Old 12-31-2011, 07:07 AM
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The center vents are for fresh or cooled air. The rear center vent on my SDL blows cool or fresh air, just like the front ones. The front centers shut off when the system goes into heating mode, the middle rear does not; you have to use the lever. Mine shuts off about 98%... there's still a small air leak but I'm not going to worry about it right now.

There are heater ducts that run under the front seats

-J

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