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I drive a 2008 Vibe which I park outside. Last weekend we had our first huge snowfall of the year. It was only -12 C, but the snow was coming down like crazy. I was late for an 8 a.m. appointment, so I just started up the car, brushed off the snow and took off. On the road, I had a hard time keeping ice from forming on the windshield. I tried everything. The logical choice, the defroster on high heat, just made the falling snow melt and the freezing worse. I had the best luck with the defroster on no heat. What is the best setting to keep the windshield clear of ice in a snowstorm? -- Kris, Edmonton

How do you keep ice off a windshield when you're too rushed to warm up the car? Simple, you don't.

"The first mistake most people make is they just assume they can hop in a car and the windshield will defrost," says Don Szarko, director of advocacy for the Alberta Motor Association.

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"When it's as cold as it gets here, you have to let it warm up and scrape off all the ice before you get on the road."

While it's still debated whether your engine needs to warm up, letting it run at least five minutes gives the defroster enough heat to work properly.

"That might not be true in Nova Scotia, but in Alberta it is," Szarko says. "It's not an eco-friendly answer, but the heat for the defroster comes from the engine, so when the engine's warm it works better."

There is an alternative: you won't have to run the engine for as long if you plug in the block heater for 15 to 30 minutes before you start your car, Szarko says.

"It'll give the engine a head start in being able to produce heat more quickly," Szarko says.

And while that heater's warming up, the windows need to be scraped clean of ice and snow. All the ice on all the windows.

"You can't just scrape a little section to see out of – it's actually illegal to start driving unless all windows are clear," Szarko says. "You see these cars that are roving snowbanks and they can barely see – in Calgary a couple of years ago a driver hit a girl in a crosswalk because he could only see through a quarter if his windshield."

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Back to the question. If you start with a warm, clear windshield, what should you do if you get ice forming while you're driving? We asked GM and they say it varies on the vehicle and on the weather.

The Vibe's manual says to use the defroster setting for ice, frost or extreme fogging, and the less heavy-duty defogger for just a little fog on windows.

What's the difference? Where the heat comes from.

Defrost (the defrost symbol) directs heat to the windshield and the dash vents, the manual says. Defog (a smaller defrost symbol plus an arrow pointing to the driver's legs) does what defrost does, but also directs heat to the floor for comfort.

In both, the A/C kicks in to dry out the air, but only if it's above 0 C outside.

"Below freezing, the A/C compressor will not run, to prevent freezing of the evaporator core which will block airflow in the HVAC system," GM spokesman George Saratlic said in an email.

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Also, if the air's not flowing properly out of the defroster, check the outside cowl just under the windshield to make sure it's clear. That's where the air flows in. Plus, if you have an older car, make sure the thermostat has a high enough temperature rating, Szarko says.

If your windshield's warm, you're blasting the defroster and the melting snow is still freezing, the culprit could be your wipers or your washer fluid.

"Wipers wear out, especially if you let them freeze to the windshield and then peel them off or just bang them free with the scraper," Szarko says. "And you should be using the winter washer fluid, the stuff rated to -40 C or -45 C."

Finally, if nothing works and ice is still forming, pull over and get out the scraper.

"There may be some situations where the vehicle is just not able to keep up with the snowfall or road spray accumulation and the customer will have to safely stop and clear the windows manually," Saratlic says.

If you have questions about driving or car maintenance, please contact our experts at globedrive@globeandmail.com.

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