I hae a '09 300 and in the winter while I'm driving the windows fog up then frost up,
i have asked my dealer about this problem and no one knows, I know other people with the same car and it doesn't happen to them, it actually gets bad enough that it could be dangerous.
The drain could be plugged from your HVAC unit allowing too much moisture to build up, the A/C side of the system may not be operating in the modes it is suppose too, that dries the air during winter months. Could also be a blend door servo not functioning. Try an independent shop, tell them exactly what is happening, as this system is computer controlled it could be a number of things. They will know how to pull the system codes and diagnosis it.
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