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How Do Car Defrosters Work?
Understanding defrosters, defoggers, and demisters
By Jeremy Laukkonen Jeremy Laukkonen Writer Shoreline Community College Jeremy Laukkonen is automotive and tech writer for numerous major trade publications. When not researching and testing computers, game consoles or smartphones, he stays up-to-date on the myriad complex systems that power battery electric vehicles . lifewire's editorial guidelines Updated on October 26, 2021 Reviewed by Jessica Kormos Reviewed by Jessica Kormos Saint Mary-of-the-Woods College Jessica Kormos is a writer and editor with 15 years' experience writing articles, copy, and UX content for Tecca.com, Rosenfeld Media, and many others. lifewire's editorial guidelines Tweet Share Email Tweet Share Email In This Article
Expand Jump to a Section Types of Car Defrosters How Car Defrosters Work Secondary Car Defrosters Other Defogging Methods Aftermarket Car Defrosters When it's cold out and you can't see through your car's windshield, you'll probably reach for the defroster button. But how does the defroster work—and why does it always seem to take forever to clear ice, frost, mist, or fog from the windshield? Learn all about how car defrosters, defoggers, and demisters work. kenneth-cheung / E+ / Getty Images Types of Car Defrosters
There are two primary kinds of defrosters. The first type uses a vehicle's heating, ventilation, and air conditioning (HVAC) systems to blow warm, dehumidified air directly onto the foggy or iced-over windshield. The other type of defrosting system defogs and de-ices through a mechanism known as resistive heating. How Do Primary Car Defrosters Work
Defrosters that use a vehicle's HVAC system are sometimes referred to as "primary" defrosters, since they are designed to clear up the front and side windows, and they work via two main principles. In order to melt ice that has accumulated on the windshield, the HVAC system activates the primary defroster to draw in fresh air, passing it through the vehicle's heater core. It then directs the warm air through dashboard vents toward the front windshield and side windows. In addition to defrosting windows, these primary systems can also defog windows by removing condensation from the inner surface. To accomplish this, a front window defroster will typically pass air through the air conditioning system to remove moisture. When this dehumidified air reaches a fogged windshield, it absorbs moisture and removes the condensation. Warm air can also hold more moisture than cold air, which is what makes primary defrosters effective when these two systems work in concert. Although it is possible to accomplish the same moisture removal process by physically wiping the condensation away, doing so may leave smudges that can result in glare; it may also make it difficult to see through the windshield at times. How Do Secondary Car Defrosters Work
Defrosters that don't use a car's HVAC system are sometimes referred to as secondary systems since they are designed to defrost things like rear windshields and mirrors. These systems typically use wire grids and resistive heating to physically warm up the surface of the glass, which can effectively melt ice and remove condensation. Rear windshield defrosters typically use surface-mounted grids that are easily identifiable, while heated mirrors usually have internal wires that you can't see. However, both systems use the same basic mechanism of resistive heating. An electrical current is applied to the wire grid when you activate the system, and the resistance of the grid causes heat generation. How Do You Defog a Windshield With No Primary Defroster
If your car has air conditioning, but it doesn't have a button you can push to automatically defrost and defog the front windshield, you can accomplish the same task manually: Start your car and turn on the heater. Set the heater to the highest setting. Changing the vent selector to the dash vents that point at the windshield helps defrost the windshield, but warming up the air inside the car is the most important factor in defogging. Change the HVAC circulation setting to draw air in from outside. Turn on your air conditioning. Open the windows a little bit. Aftermarket Car Defrosters
Since OEM systems make use of both primary and secondary defrosters, aftermarket replacements and alternatives are also available for both types. In particular, grid-style rear defrosters can be repaired by conductive paint and adhesive materials, or scraped off and replaced altogether by aftermarket defroster grids. Although no direct replacement exists for primary defrosters, 12V car defrosters operate via the same basic mechanism of action as OEM HVAC defrosters. These devices cannot heat up the same volume of air as a traditional HVAC system, but they still work by directing warm air at a fogged or iced over windshield, and they are a viable alternative to a broken defroster in some cases. Was this page helpful? Thanks for letting us know! Get the Latest Tech News Delivered Every Day Subscribe Tell us why! Other Not enough details Hard to understand Submit More from Lifewire Finding a Cheap Fix for a Broken Defroster 9 Things to Consider Before Buying a Dash Cam Do Car Air Purifiers or Ionizers Really Work? How to Fix a Stuck Car Window The 8 Best Portable Electric Car Heaters of 2022 What Android Auto Is and How to Use It Block Heaters vs. Remote Starters: Which One is Best? How to Fix a Car Horn That Won't Stop Honking 5 Fixes for a Broken Car Heater How to Remove Smoke and Cigarette Smells From a Car 10 Appliances You Can Plug Into Your Car What Are Fog Lights and Are They Worth It? Can a 12 Volt Car Battery Really Electrocute Someone? How to Fix Gross Car Heater Smells Choosing a 12 Volt Car Heater How Much Does It Really Cost to Warm up a Car? Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. Cookies Settings Accept All Cookies