Heater Mists up entire car

[Parisien]

Thanks again Hotrodder!


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[Parisien]

So, after further investigation, all 4 holes as clear as they can be, ie not blocked, we checked the function of the flow of warm air to the windscreen to find it almost non-existent, other settings were fine.

If someone can nail down likely cause and how to fix, as ever eternally grateful!


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PS Also noted my rear screen heater aint working either ......the screen has been replaced, where are the wires routed to supply the screen's heater element?

PPSS AS I've not got the manual for car whats the button above the EC button with two vertical wavy lines for?

 

[LostKiwi]

So, after further investigation, all 4 holes as clear as they can be, ie not blocked, we checked the function of the flow of warm air to the windscreen to find it almost non-existent, other settings were fine.

If someone can nail down likely cause and how to fix, as ever eternally grateful!


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Sounds like the vacuum system for the vents isn't working properly though normal failsafe is windscreen vents and outer face vents..

PS Also noted my rear screen heater aint working either ......the screen has been replaced, where are the wires routed to supply the screen's heater element?

PPSS AS I've not got the manual for car whats the button above the EC button with two vertical wavy lines for?

According to my manual its 'dehumidifier'. I find my SL demists best with no lights on either EC nor the dehumidifier button.

 

[Parisien]

Thanks Lostkiwi, where are the vacuum pipes to fix, starightforward or part dismantle dashboard?

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[LostKiwi]

Thanks Lostkiwi, where are the vacuum pipes to fix, starightforward or part dismantle dashboard?

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In the area next to the ECU there is a vacuum distribution block (assuming same as r129). These have a habit cracking and leaking. A dab of epoxy will sort it in no time.
From there there are a raft of vacuum lines one of which goes into the vent control block behind the glovebox. If there are any vacuum leaks in the system the whole lot plays up.

As I say though - normally the failure mode results in windscreen vents working along with the two side vents but you can't redirect it anywhere else.

 

[Parisien]

Thanks for that, so I need to remove glovebox if required, tips?

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[LostKiwi]

Good article here about how it works and how to remove the glovebox:
http://www.benzworld.org/forums/w12...nually-controlling-center-footwell-vents.html

 

[Parisien]

Great, thats very useful, again anyone know where the power feed is for the rear screen or anything else which may go wrong with them?


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[hotrodder]

The air direction flaps are only driven by vacuum with automatic climate (single temp wheel and push buttons for everything else as in the benzworld link). Demist/dehumidify button above the EC button suggests dual zone aircon, the rotary air direction knob moves cables which drive the direction flaps with this set up... google images 1248300185

Dunno if it'll be accurate for UK models but http://www.w124performance.com/service/Index/Groups/82LightsWipersRadio.htm has a wiring diagram for the HRW and if you go back to the main page and look in section 67 (windows) the connections are probably covered under fitting the rear window... if you run a finger around the screen rubber you should find both of the cables where they're routed around the rubber. On the estate they're at the bottom corners of the screen, dunno about coupes

 

[LostKiwi]

My 129 has dual temp thumb wheels and two rotary controls and a dehumidifying button and is manual AC and all vents are vacuum driven. Demist mode is one click past fan speed 5. I don't know but would have thought the 124 was the same?

 

[Ben Longden]

Guess you have nailed it!
AC dries the air coming IN to the cabin. Warm air evaporates the water already in the air inside the cabin.

Memo; dont wipe the inside of the screen with your hand or a hanky. This just smears crud everywhere. Use the AC to dry the screen. Keep it clean it with glass polish then regular windex glass cleaner.


Finished a gig at Swan Hill one night. 30 degrees and a hammering storm. 135Km trip ahead to get home and Roo city all the way. Started the W124 (this as several years ago), and voila! All glass fogged up. Switched on AC, set vents to windscreen, set temp to 24, recirc OFF and 30 sec later fog cleared.

 

[Parisien]

In the area next to the ECU there is a vacuum distribution block (assuming same as r129). These have a habit cracking and leaking. A dab of epoxy will sort it in no time.
From there there are a raft of vacuum lines one of which goes into the vent control block behind the glovebox. If there are any vacuum leaks in the system the whole lot plays up.

As I say though - normally the failure mode results in windscreen vents working along with the two side vents but you can't redirect it anywhere else.

Ok, so pulled out glove box to find no evidence of a vacuum control box, so perhaps its behind the instrument panel section?

Can anyone confirm and give guidance as how to access/fix?

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[Jim2]

My problem, which I only noticed last Friday night, when we had the temperature hovering around the "0" or even " -1c, and the windscreen was completely frosted over. I set the temperature controls to HI, with both the front and rear screens electric elements switched on. After a short wait ( few mins ) the front screen at the Drivers side, and center, cleared, but the passenger side took quite awhile to clear. The rear screen was not a problem, and cleared pretty quick. Do these symptoms fit a recognized pattern? The car is a 2010 Mercedes E class w212, 200 CDI.
Thanks for your help.

 

[LostKiwi]

Suggests you may have moisture somewhere in the car.

 

[Jim2]

Suggests you may have moisture somewhere in the car.

If it is moisture that is causing it, would that not affect all of the screen? It gives the impression that a air duct is blocked or a fan is not working on that side? With individual climate control. I presume that there would be separate fan for each of the duct's?
Is there a generic fault that generates moisture in them? I did have a passenger in the front with me at the time, if that would affect it in any way???
Thanks Lost Kiwi.

 

[LostKiwi]

Moisture on the left side would give misting on the left. For example a blocked AC drain or leaking windscreen seal.
A vent could cause it - a star session can soon prove this by performing actuations on each flap and checking results (did exactly this on the r230 today).

 

[Jim2]

So it's fresh in your mind then, Lost Kiwi. I have to replace the cabin filter this week in any case, so maybe the vent ducts would be visible, once the filter was down? ( I have never changed this before, so I really don't know what ( if anything ) would be visible then. I will check the A/C drains too while I'm at it. Would it have to be done on a STAR, or would it show on the iCarsoft MB11 that I have?
Thanks again, Jim2,

 

[LostKiwi]

No idea on the i980 sorry. Star allows you to actuate the vents and then compare the expected position values against the actual values. No idea if the i980 will allow you read the position values or not.

 

[Jim2]

Its not the i980 model, it's the one that replaced it, the MB11 ( which was itself replaced by the MB V 2 not too long ago) Meanwhile. I will see what I can check physically.
Thanks again.