Air conditionting question?

I have a 89' 560 SEL. My question is this does anyone in the group experience this problem, I was driving last night and the humidity was up about 95%. All of a sudden, the windshield starts to fog up and I'm losing
visibility. I pulled over and notice the condensate (fog) was on the inside of the windshield. I had the outside air closed off. I finally let it sit (took off the a/c :o( ) and went home.
My question does this happen to anyone in this group? Also, is there a cure for it?
Bill G.
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I have seen this is my 1986 190e... Opening all the windows is the only cure I have found to date... Pretty dangerous if you are at speed.
Marty
PS I have a feeling that the AC is cutting off at this time?
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Did the condensation build from the bottom of the windshield (near the defroster vents) and then work its way up? If so there may be a vacuum leak that is causing those vents to not close completely. I had a similar situation on a '95 E320 and it was solved once the leaking vacuum line was replaced.
Also, there can sometimes be difference in windshield fogging due to air re-circulation (I seem to recall on an old Mazda I had to ensure that the recirculate was off when it was extremely humid).

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It may be nothing more than a simple matter of physics: cold air blasting on the warmer windshield lowered it to or beyond the dew point... hence the fogging. The extreme humidity present exacerbating things. If the problem does not persist during more normal conditions, case closed!
This is a phenomenon that amateur astronomers (like yours truly) deal with on a regular basis... fogging of the optics on our telescopes as they acclimate to the dropping ambient temperatures. We use specially designed heaters to keep the optical surfaces just a tad above the dew point.
You might try leaving the AC on but increasing the temperature setting so as to remove the fog, then return to a more comfortable setting once the windows have cleared.
Paul
--- http://www.astro-nut.com ---

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Majority of the problem is two fold... first, your seals on the defrost vents are bad... allowing cold air to escape to the windshield and causing the fog.
The second reason is that your defrost vent actuator has failed... but there is two reason for this failure... One is if it is wide open all the time, then it is your vacuum actuator that is bad. If you were accelerating or going up the hill and noticed air coming out of the defrost is stronger, then your yellow checkvalve is bad.
Lastly, is your air conditioner cold? If it is not, then you need a recharge.
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Before my current part eater, I had a 400 E that did the window fogging trick in humid wether. I took it to Hanz und Franz and they just shrugged and called in normal. So maybe it is normal. Of course Hanz und Franz at Heavy Carl's had also wanted 1500 to decarbonize my intake manifold to fix the yellow engine light when all that was needed was a relay in the circuit! Maybe you should have Tiger flown in to your kar and let him fix it.
mcbrue unfoggedly under the bridge in the trailer down by the river
96 S420
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How does one get to the actuator?
Thanks,
Joe

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Through the glovebox... you open the door... take out those six or 8 double anchors out... I meant double... you have to slide the top out to get the bottom out of each anchor...
Then your glovebox is loose... pull it out and the actuator should just be at the left hand side... push it in and you will know which actuator you just controlled...
Now.... I haven't look closely at the R107 so I don't even know if you have a glovebox there like the W126.
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Thanks, I'll look this weekend!

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My '86 560SL does the same thing. Most of my air conditioning air always comes out of the defroster vents. I live near the coast where it is humid most of the time so I get the fogging most of the time.
I wish I knew how to fix it because I want the cold air on me!!!
Joe

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