As winter is now here a functional defogger is a requirement yet this year my car won't defog no matter what I try.

All vents in the car are functional and blow whatever is pumped through them (eg I don't think there is a block of any kind, and both hot and cold work)

What I've noticed is that my model doesn't have a toggle for "recirculating" the air inside the car vs. pulling in fresh air.

Long story short the best I can do is full fan, set to defog, with the temperature on COLD. Although this keeps the windshield and driver/passenger windows mostly clear it isn't ideal when its freezing outside (I live near Toronto Canada, so it's a full 4 moths of winter)

These are the controls I have: enter image description here

Is there a part of defog that should work like A/C that tries to remove humidity from the air?

Update: I didn't have any luck last winter resolving this but it turned out to not be a major issue weather wise. This year the problem has returned so I took it into my local shop. They found no issue with the heater, fan etc. and couldn't find any issue that would cause this. I'm now going to look deeper to see if I can find any leaks into the vehicle where moisture is getting in, check the cabin filter isn't dirty/oily/wet etc. I may also return to my dealer to see if they have any "known causes" that might be of magical assistance.

  • The A/C was working in the summer... But that was at least 4 months ago :-)
    – scunliffe
    Commented Dec 30, 2012 at 18:06
  • I have the same problem, even with the ac button on, newer 300 have a air channel built into front doors, can not solve my issue either
    – user4368
    Commented Jan 23, 2014 at 1:42
  • Did you ever figure out the problem?
    – user7338
    Commented Oct 27, 2014 at 13:39
  • Sadly no. It's been -15 to -20 degrees (before windchill) this week so it's rather annoying right now.
    – scunliffe
    Commented Jan 10, 2015 at 20:59
  • We have a 2008 300 with the same problem and we are in Ottawa. I took the car to the dealership twice last winter but the days we had it in, the weather was above freezing and there was no problem with the defogging. I am 100% sure this is an issue with the recirculation of the air in the cabin because the more bodies you have in the car, the worst the fogging is and the faster it builds up.
    – user9091
    Commented Jan 13, 2015 at 19:59

3 Answers 3


The defrost setting (left most position on the right knob) should cycle the a/c and blow dried air onto the windshield. The a/c should dehumidify the air the result of which is less fog. The recirc function you are looking for is the two right most switch positions. This is not the selections you want for defogging. The humidity in the cabin will not be removed but recirculated. The most common causes for fogging issues are leaking heater cores, do you notice low coolant levels, a sweet smell when the fan is on, or an oily film on the windshield interior, all indicate a leaky heater core. Another cause is a leak that allows rain into the cabin. As it evaporates the humidity increases. If the heater box drain is plugged the moisture that the a/c unit removed from the air collects in the heater box and is recirculated resulting in fogging.

  • Thanks for your answer... I don't see any low coolant levels, smell sweet air (though a friends car had this once so I know the smell), and no oily film on any interior window. I'll see if I can locate this heater box and see if the drain is plugged ;-)
    – scunliffe
    Commented Dec 30, 2012 at 1:50
  • So the A/C does work (it cools fine) in the summer... though I have noted in the first 30 seconds or so that sometimes there is an odor... but not sweet... more like a slightly "sweaty" smell but it goes away quickly.
    – scunliffe
    Commented Jan 10, 2015 at 21:01

I have the same problem with my 2010 300 and I now think it is a design flaw. Later models have fixed the problem with door vents that help.

I am also in Ontario and this winter <2015> is proving to be tough for fogging the windows. What seems to work is running the defog on full blast (which is noisy, unfortunately) and keeping the temperature inside at about 20 Celsius. Warmer temperatures seems to make the problem worse.

What also works is leaving a couple of windows cracked open. This makes driving visibility better, but makes driving comfort pretty low.

What doesn't work, in my experience, are any window-treatment products that are available. None have been successful in my experience.

The heater core, coolant hoses and system and vents were all in good working condition in my 300, but the windows are always fogged up regardless. I've never had such a problem in any other car that I've owned.

I've also noted that in the summer the air conditioning has to be turned up to a high fan speed to feel effective, which makes me wonder if the car just has a lousy comfort system. The car is great, otherwise, but the fogging windows is a serious negative.


You need to have the AC button on. The Bottom left center with the snowflake. That switch has to be on for the AC compressor to activate. I have no idea why some manufactures choose to design cars this way. You can have the temp in any position so you can still have heat, you just need the AC switch on for the AC compressor to activate and dehumidify the air.

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