Thanks for the responses everyone.
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Do you smell anything inside your car? Sweet smell means coolant, musty smell means mold from an outside leak.
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I have not smelled anything out of the ordinary.
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Failure to remove as much snow as possible from shoes before entering the car
Failure to remove wet floor mats from the car in order to dry them
Keeping windows open, rather than using the HVAC system (on the A/C setting if necessary)
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I think the floor mats are adding to the moisture in the car. I don’t remove the floor mats. It gets really cold up here in Canada that when I am done driving, I just want to rush indoors.
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Try running your air conditioning to keep your cabin dry, even if it’s cold out. Leave the a/c on, but use the heat control to stay comfortable. You will still be warm, but the air will be dry, which will probably help a lot.
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I will do this.
Thanks everyone!