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Windshield defogging, or, is it defrosting? Or de-icing?

By Steve Schaeber, MACS Service Training Specialist
It’s a cold winter’s morning, you’re running out the door on the way to work or school, and you get in your car only to find that the windshield is all clouded up, either with fog, ice or snow.
After letting out a sigh of aggravation, you get started with that winter morning ritual of clearing off your windows.  If you’re lucky, there’s no ice or snow to remove.  If you’re not so lucky, you’ve got some work to do.  Those of us who live in the great northeast and other northern parts of the US and Canada know this scenario all too well.  But what we may not know is how to clear our windshields in the most expeditious manner, so we can get on our way quickly and safely.
There are a couple of schools of thought on this, and a quick search on the internet will yield more than a few results.  So, here are some MACS Quick Tips on how to get clear and get going.
Clearing your car in the wintertime is all about heat, and the more of it, the better.  But more than that is the combination of temperature and humidity, which is where the HVAC system comes into play.  Let’s look at how to set the controls to get the best performance possible.
•    Start your vehicle.  This is the most important step, and should be done first.  The heat produced from the running engine is ultimately what will clear your windows.  But this doesn’t happen very fast.  It takes time for an engine to reach its normal operating temperature, and the colder it is outside, the longer it takes to warm up.  Make sure you allow enough time for this to help get your windshield clear.
•    While you’re waiting for the engine to warm up, there’s more to do.  If there is any snow or ice on the outside of the vehicle, you should get out and clear it off.  There are important reasons for this, one I’ll talk about now, and one I’ll mention later.  For now, removing that ice and snow will make it much easier for the HVAC system to work because you’ll be removing all that excess material that would otherwise take a long time to melt away.
•    Setting your HVAC controls to the proper settings will allow that first bit of warm air to start working for you as soon as it’s available.  While manufacturers differ in what they recommend, here’s basically what they say:
•    Set the fan speed to high.  This will move the largest volume of air, which will then transfer the most amount of heat, and remove the most amount of moisture.
•    Set the temperature setting as high as it goes.  This will allow all of the possible heat to transfer inside the vehicle where it’s needed most.
•    Set the vent control to windshield.  This setting goes by a few different names, and does a few different things, depending on the vehicle.  But mainly it directs the flow of air towards the windshield to help clear it off.
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•    If your vehicle has air conditioning, make sure it’s turned on.  Some vehicles do this by default when you select “windshield” on the controls, and some do not.  Now here’s where you may be asking, “Why would I want to run the A/C when it’s so cold outside already?”  And you’d be right to think it’s silly to use A/C in the winter.  But there is a method to this madness.  The reason for running the A/C is to remove moisture from the air; the same moisture that causes windows to fog up.
•    You’ll also want to turn on the rear window defogger, if equipped on your vehicle.  This turns on a heating element that is built into the rear window glass, and directly raises its temperature to remove ice and fog.
•    Last but not least, give it some time.  There’s nothing more dangerous than driving a vehicle that you can’t clearly see out of.  It’s not just unsafe for you and your passengers, but also for other motorists on the road around you.
In some states it’s actually illegal to drive your vehicle unless it’s clear of all ice and snow.  There have been accidents due to a sheet of ice flying off of a moving vehicle and striking the windshield of the car behind them, killing the driver. Always put safety first!  A few extra minutes to clear off your car can help prevent a tragedy.
If you’re lucky enough to have automatic start, or remote start,  check your owner’s manual about how to use this feature.  When used properly, it’s really convenient on these cold winter mornings.  But remember, in order for the remote start feature to work best, be sure to set your HVAC controls to the proper settings before getting out of the car the day before.  It would not be fun to use the remote start, thinking you’ll be getting into a warm car, only to find out that you didn’t set the controls properly the last time you were in the car.
So, time to go find that ice scraper brush that’s been put away in the trunk, under the seat, or in the garage for the summer.  Chilly mornings are surely in our frosty-window future.
The Mobile Air Conditioning Society’s blog has been honored as the best business to business blog in the Automotive Aftermarket by the Automotive Communications Awards and the Car Care Council Women’s Board!
When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.

If you’re a service professional and not a MACS member yet, you should be, for more information.

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The 34th annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Power Up will take place January 16-18 2014 at the Sheraton New Orleans.

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