This is the Fastest Way to Defrost and Defog Your Windshield

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Winter driving is hazardous enough when you can see where you’re going. Reduced visibility due to a foggy or frosted windshield can quickly create a hazardous situation. Body heat and breath create a warmer environment inside the car than outside to form condensation. Moisture in the air sticks to a freezing cold windshield, and needs to be scraped or melted away to restore visibility.

While wiping the condensation off the window may seem like the best idea, it actually isn’t. Wiping the windshield leaves streaks that can reduce visibility and create distractions even after you’ve gotten rid of the frost and fog. According to Tom’s Automotive Service in Seattle, Washington, a better way to defog your windshield is to let the car’s air conditioning system do the job. Use an ice scraper or commercial de-icing product to quickly remove ice from a frosted windshield.

How Does Air Conditioning Work As a Windshield Defog?

Your car’s air conditioner defrosts your windshield in two ways. First, it removes moisture from the air inside the car. That’s right: An air conditioner is also a dehumidifier. In fact, the first air conditioners were invented by people trying to make a better dehumidifier.

The second way an air conditioner works as a windshield defog is by reducing the temperature in the vicinity of the windshield to prevent new condensation from forming.

How to Defog a Windshield

It’s simple: Turn on the AC and aim the vents up so the airflow hits the windshield. The AC system will remove moisture inside the vehicle by circulating the air through the cold fins in the evaporator. Of course, the problem with this method is that running the AC will make the environment in the car uncomfortably cold, and no one wants that in the middle of winter.

Auto manufacturers know this, which is why they install a defrost system in every car. As Tom’s Automotive says: “When you turn the defrost on, it’s your air conditioner that kicks in to help get all that moisture out.” The defroster fins already point directly at the windshield, so when you use it — and not the AC system — the car will stay warmer. If you want the defroster to work faster, try this trick: Flip your visors down. They will redirect the air flowing upward back toward the windshield.

If your vehicle doesn’t have air conditioning, or it doesn’t work, turn the blower on high, flip your visors down and open your windows a crack to allow moisture to escape.

FAQ

Can defogging too fast damage a windshield?

If you use your car’s AC as a windshield defog tool, there’s very little chance of damage because it blows cold air. Your defroster is also safe because it won’t blow warm air until the car heats up, which happens gradually. However, if you get impatient and try to defog by using a hair dryer or pouring hot water, the sudden temperature change could crack the glass.

Do spray-on defrosting solutions actually work?

“Yes, they work well,” Larry Morrison of Napa Auto Parts says. “There’s the kind that you can put in the reservoir itself or aerosol products that are a little more potent.” Defrosting solutions work by leaving a moisture-repellent film on the windshield that prevents condensation from sticking to the glass and turning into ice. Any commercial product is suitable, but you can make your own. According to Tires Plus, any of these solutions will work as a spray:

• Rubbing alcohol and water;
• Pickle juice;
• Vodka and water.

About the Expert

Larry Morrison is the manager of Napa Auto Parts in Gatlinburg, Tennessee. A former auto mechanic, he’s been in the auto parts industry for ten years.

Sources

• Tom’s Automotive Service: Defroster Not Doing Its Job in Your Vehicle?
• Tires Plus: How to Make Your Own Windshield Defroster Spray, 2024