a/c puts fog lines on the windshield
 

Why do Mercedes W124's put a fog line on the windshield? I have to use my windshield wipers on hot dry nights in the summer.

Also, my fan is squealing. I did some searching on this forum, and found there's some fan kind of thing that needs to be oiled, behind the glove compartment. Can anyone second that? Seems very easy to do. But when the blower fan is off, there's no noise. So does that mean it's the blower fan, or the thing behind the glove box?

2nd.

I cannot believe you guys are complaining
 

About anything "Frosty" in the cabin of an older Mercedes in the Summer!

Bring on the Ice Cubes!

I am pretty sure this is a result of failed vacuum pods in the HVAC system. My car never did this (was fine for a couple years) until it suddenly started. I noticed it at the same time when I noticed a reduction in the volume of air coming through the center vents when I was using AC.

I believe that air normally intended for the cabin through the center vents is instead being routed up at the base of the windshield, due to one or more failed pods.

Rgds,
Chris W.
'95 E300D, 301,750 miles

It could also be a vacuum hose that has an issue in the engine compartment. Reason I say this, I had the same issue where the center vents weren't functioning properly. After careful inspection of the vacuum system, I found a defective hose that fed the pod controlling the center vents. Rectified that and the vents functioned correctly, diverting the air to the cabin instead of to the window.

There is an aspirator motor that draws air over the cabin temp sensor by the sunroof switch. The aspirator motor is active even if the ACC is off. It's right below the passenger side dash vent. You can get to it by removing the glove box liner but access is much better if you remove the dash register as well. There are 4 clips holding the dash register in place - pry the lower ones up and the upper ones down at the same time then extract the register.

This assumes you don't have a passenger side airbag. If so, I'm not sure if it's easier to go in from the dash vent or from below by removing the lower dash panel.

If only hear the noise with the blower blowing (e.g., engine running, ACC off), check the DIY guide on getting to the blower under the wiper mechanism.

Sixto
87 300D

Frost line?
 

What is this "frost line?"

The 2500 foot line around Lake Tahoe :)

I think they mean the lower part of the windshield frosts when the AC compressor is engaged.

Sixto
87 300D

Maybe in parts of the world with high humidity? I've never seen such a thing. Fog yes, frost no.

it could be a combination of bad vac pods and old foam that deteriorates on the flap so that you don't get a good seal.

"fog" on the windshield, not frost
 

I meant to say a line of "fog" on the windshield, not frost.