Q: How do I keep the insides of my car windows from fogging up?

A: A couple of weeks back, a reader had a car-heater related question that Mankato mechanic and repair-shop owner Joe Miller answered. Miller had heard the question countless times and said people usually have a pair of follow-ups — about faster defrosting and about the insides of windows fogging up.

With Christmas over and nothing but the frigid monotony of January facing Minnesotans, it's time for the answers.

"Windows fog when they're cooler than the moist air around them, just like a cold glass of lemonade gets wet in the summer," Miller said. "So to stop fogging do one of two things: dry the moisture out of the air or warm up the window glass."

A car's defroster is designed to do both by doing something most people wouldn't expect — blowing warm air onto the glass and simultaneously running the air conditioner to dry out the air, Miller said.

"Yup. When you select 'Defrost' on your car, the A/C turns on, too, and pulls moisture out of the air and then the heater warms the air back up again and blows it onto the windows and you. The heater is built a little bigger than necessary just so it can do that."

So if drivers are having trouble keeping the windows clear, it could be that the air conditioner isn't working. But the first thing to check is that the controls are set to "Defrost" and that the button for recirculating air isn't mistakenly turned on.

Outside air is needed, even if in January.

"Again, this seems counter-intuitive, like leaving the front door open on your house while the furnace plugs away, but on a car it's all about moisture," Miller said. "The outside air is cold but also dry. The inside of the car has people breathing, and snow melting from shoes and coats and all that moisture ends up on the windows. The 'Recirculate' button should only be used to keep out humid air in the summer. If you mistakenly have it on in the winter, it traps humidity inside the car."

Q: How do I make my defroster work quicker? I know leaving my engine idling wastes gas but how can I drive around if I can't see out the windows?

A: "This one's tough," Miller said. "The easy answer is keep your car in a garage. ... But if you're not made of money, you just park on the street like I do."

Ask Us Guy always assumed that frost fell from the sky, and that's why even an unheated garage kept windshields clear. Not so, according to Miller. It's all about condensation, just like the sweating lemonade glass.

"Believe it or not, the reason your windshield is frosted up is because the glass is slightly colder than the surroundings," he said. "Just as the sunshine warms you during the day, the night sky pulls warmth away — cooling your exposed car."

To reduce frost, something is needed to slow the heat loss into the cold night sky.

"A fabric car cover, a carport without walls, even an old rug thrown over the glass will help," he said. "By the way, this also explains why after you've scraped the windows clear, they frost right up when you drive away. They're still ever so slightly colder than the surrounding air."

Miller advises against trying to clear a light frost with the windshield washers: "You'll find this a very temporary fix as the glass freezes up again in seconds as the washer fluid evaporates, and in fact it makes the problem worse because the cold fluid keeps the glass from warming up."

Q: Who is in charge of picking up the trash under the North Star Bridge and by the train trestle? There is always trash there, and I can't believe the city can't see it! It's the only part of town that has so much trash all year.

A: Typically, city crews clean up the right-of-way along that road about once a year, maybe adding mulch where needed, Mankato City Manager Pat Hentges said. But most of the land beneath the bridge is privately owned — a former concrete plant that's being steadily redeveloped into housing and possibly, in the future, offices of some sort.

Private landowners are required to keep their property clean, and the city can order a cleanup or even do the work and assess the property owners if they fail to comply. The city generally only does that for large items such as mattresses, old appliances and other oversized pieces of junk that people dump.

Ultimately, the best solution to litter is prevention, Hentges said.

"Unfortunately, like with highway ditches, people throw stuff," he said, suggesting a revival of the anti-litter initiative by President Lyndon Johnson's wife. "We need a few more Lady Bird Johnsons. Maybe Mrs. Trump can go on that campaign."

Contact Ask Us at The Free Press, P.O Box 3287, Mankato, MN 56002. Call Mark Fischenich at 344-6321 or email your question to; put Ask Us in the subject line.

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