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Door ducts

Started by 1980sdga, 22 October 2011, 06:53 PM

1980sdga

I've seen some discussion about the "door heat" ducts.  Are they supposed to blow through the door panels? Around the front edge?

MB obviously put some thought into it as evidenced  by the little rubber bellows and heavy ducts under the dash.  I've noticed that the carpeted panels act as radiant heat for the footwells so is that it?  Kind of radiant heat from the doors?

Mforcer

I think the door cavity is designed to be heated/cooled and insulate the interior passengers from the outside. Insulation is much more comfortable than simply blasting hot/cold air into the cabin.

I also don't see how the carpeted areas would provide radiant heat to anywhere. Perhaps you are missing the insulation behind the dash and footwells.
Michael
1977 450SE [Brilliant Red]
2006 B200

Big_Richard

i think from memory, one needs to ensure they still have the clear plastic films in place over the insides of the doors otherwise that air is just going to blow inside the door and out the car  8)

Mforcer

I thought the plastic was to keep any water out that drips down the glass.
Michael
1977 450SE [Brilliant Red]
2006 B200

1980sdga

I was referring to the carpet that covers the plastic ductwork under the dash:



There are no vents blowing air at your feet. The air just goes straight through to the doors but it warms the ducts/carpet up quite a bit as it travels through. 

Mforcer

I will need to double check but I think there is a small hole in that duct work that opens to the foot well. The hole is small enough that I initially thought it was just to allow dirt to fall out of the duct but it could allow for enough venting to that area.

I think any heating of the panel under the dash is more a result of heat from the engine. If heat was meant to come through that area as you suggest, they would not have added carpet which would insulate the heat transfer more than the original non-carpeted plastic panels.
Michael
1977 450SE [Brilliant Red]
2006 B200

Big_Richard

Quote from: Mforcer on 23 October 2011, 08:12 AM
I thought the plastic was to keep any water out that drips down the glass.

yes it does, but from memory if its not present the air will just go in the door and out the car ;)

1980sdga

I have another car that has the footwell duct part disassembled. I'll check it out as well.  Thank goodness I'm not getting any engine heat bleeding through there! I drove it for quite a while in the warm weather with no ducts and didn't notice anything getting warm. It's just with the heat on.

I'm running without the carpet panel on the drivers side and that's when I noticed how warm the duct gets. I reached over to the passenger side and felt the carpet and it's warm as well.

Mforcer

Quote from: Major Tom 6.9 on 24 October 2011, 12:57 AM
...b    the air will just go in the door and out the car ;)


I am suggesting that the air is meant to cool/heat the door cavity and not an issue if it does escape out the car.


I could be completely wrong but I would think blowing cooled/heated air onto the door panel as opposed to into the cavity will not achieve much.
Michael
1977 450SE [Brilliant Red]
2006 B200

Big_Richard

well the plastic covers are supposed to be on the doors so i doubt the air is meant to go inside the door body, i think its supposed to go inside the door panel warming the whole thing and or allowing some to leak out around the arm rest ?

Gerard

I recall reading somewhere that the door trims were heated so warm air passed over the side windows keeping them free from condensation.  I always tried to feel for warm air rising up the window glass, and looked for a gap between the door trim and glass but never "felt" any air.

Heating from the underside of the parcel shelf is probably not in the design, air at that temp (I'm guessing 40-60degreesC)  would conduct very poorly from the duct, across an air gap, onto the trim, and through the carpet.  Eventually it would warm up, but as a deliberate source of heat, unlikely in the design.  The forced air vents (convective as opposed to radiative) are the primary means of heat transmission there.






Mforcer

Thinking about this more, if the actual panel is intended to be heated/cooled, there is the question of how well it will transfer that heating/cooling and I would think that venting onto the panel itself will not dissipate in any meaningful way.


I am standing by the idea that the vent is into the door cavity itself and relatively little is lost to the outside of the car.


Do people have photos of original door panels? I suspect mine have been changed at some point.
Michael
1977 450SE [Brilliant Red]
2006 B200

Big_Richard

Quote from: Mforcer on 24 October 2011, 04:59 AM


I am standing by the idea that the vent is into the door cavity itself and relatively little is lost to the outside of the car.



with all due respect, BS!  ;D

arman

#13
I always thought that the foam sheet behind the trim was of an 'open cell' type which means that the vent air passes through it and through the corduroy cloth of the door trim.

After 37 years the original foam sheet has fallen into small pieces and all pieces gather where the corduroy/cloth meets the plastic bottom panel of the door trim (just above the pocket where you put maps and stuff).

I think it was MB's intention to create a smooth and comfortable flow of air through the door panel cloth, which was probably an innovation in those days (begin '70). I think it also helped to create the individual temp setting possibility (one for driver and one for passenger) which also was something new those days, I think.
I'm not writing facts here, I'm just contemplating.

But I've seen some discussions saying that this solution has saved many doors from rusting away :) It's a shame they didn't implement this in the back doors as well. I'm not sure but I think the foam in the back door trim is of a 'closed cell' type and holds much better after 37 years.

Originally however I don't think MB's intention was to blow air into the door cavity and out of the car, but to keep the warm or cold air inside the cabin to serve the driver/passengers.
1974 W116 450 SEL 340.000km
Black exterior (040), olive green velours interior (966)
[url="http://gallery.w116.org/v/show_room/Armans450sel/"]http://gallery.w116.org/v/show_room/Armans450sel/[/url]

TJ 450

As Arman has said, the air is prevented from entering the door cavity, as the ducting terminates at the outside of the door card. In the case of MB-Tex trims, the material is perforated.

Clearly, that is why the foam on the front trims differs from the rear.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500