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Defogger in Car: Rear & Front Car Defogger and How to Use Them

TeamAckoJan 18, 2024

Imagine a chilly winter morning; you're running late, hop into your car, and just as you're about to pull out, you notice your windows fogging up. Your clear view is suddenly clouded, both literally and metaphorically. It is where the unsung hero of our vehicles, the defogger, steps in. It's not just a luxury or a fancy feature; it's a necessity. A car defogger ensures that your view inside remains crystal clear regardless of the weather outside.

Additionally, it enhances road safety greatly. On average, 14 lives are lost daily due to foggy weather conditions. Hence, a Defogger is indeed a must. In this blog, we'll explore the magic behind the defogger in cars, how to use it effectively, and why it's crucial for safe driving.




What is a Defogger in a Car?

A defogger is more than just a tool; it's a guardian of clear vision. That silent companion ensures your driving experience remains safe and enjoyable, especially during unpredictable weather conditions. You might have noticed your bathroom mirror getting steamed up after a hot shower. We know it is called condensation. The same phenomenon occurs in your car. When the warm air inside your vehicle meets the cold windows, it turns into water droplets or fog. It is where your friend, the defogger, steps in.

Most cars come equipped with two types of defoggers: one for the front windshield and another for the rear. The front defogger typically works by blowing warm air onto the windscreen via the car's vents, ensuring the glass temperature rises and preventing condensation. 

On the other hand, the rear defogger uses a slightly different mechanism. Those thin lines you see on your rear windshield? They are electrical heating elements. When you activate the rear defogger, electricity flows through these lines, heating the glass and evaporating any moisture present.

But why is this so important? Imagine driving on a highway with fogged-up windows. Not only does it obstruct your view, but it also makes it difficult for other drivers to see you, especially from the rear. It's not just about clarity; it's about safety.

Types of Defoggers in Cars

When it comes to ensuring a clear view while driving, car manufacturers have equipped vehicles with specialized systems designed for both the front and rear windows. Let's dive into the two primary types of defoggers found in most cars today.

1. Rear Defogger in Car

Description and Functionality: The rear defogger in the car, often noticeable by the grid of thin lines running horizontally across the rear windshield, is an electrical system. These lines, made of a conductive material, heat up when electricity passes through them. Once activated, the heat generated by these lines quickly dissipates the fog or frost formed inside the rear window. It's a simple yet effective mechanism that doesn't rely on the car's heating or air conditioning system.

Importance of a Clear Rear View: While the front view is vital for a driver, the rear view is equally crucial. A fogged-up rear window can obscure the view of vehicles behind you, making lane changes or reversing manoeuvres risky. Moreover, in heavy traffic or while parking, a clear rear view ensures you're aware of your surroundings, preventing potential accidents or collisions. It's not just about what's in front of you; it's also about what's behind you.

2. Front Car Defogger

How it Differs from the Rear Defogger: Unlike the rear defogger, the front defogger doesn't use electrical lines on the windshield. Instead, it leverages the car's heating, ventilation, and air conditioning (HVAC) system. When activated, the HVAC system directs warm air to specific vents at the front windshield's base. This warm air rises and covers the entire windshield, effectively clearing any condensation or frost.

Its Role in Ensuring a Clear Windshield: The front windshield is the driver's primary window to the world. Any obstruction, fog, frost, or even heavy rain can severely impact driving safety. The front defogger ensures that the driver always has a clear, unobstructed view of the road ahead. Whether navigating through a bustling city or cruising down a serene countryside road, the front defogger guarantees that your journey remains safe and enjoyable.

While both defoggers serve the same primary purpose - ensuring clear visibility - their mechanisms and functionalities differ. Together, they form an integral part of a car's safety system, proving that sometimes, unseen features play the most significant roles.

How To Use Defogger In Car

It is a simple process if you are wondering how to use a defogger in a car. Although in some cars, controls and features may vary based on the make and model of it, the basic idea remains the same. Here are ways to use a defogger in a car:

Front Window Defogger: 

  • Start the car

  • Activate the defogger

  • Adjust fan speed and temperature 

  • Switch of the air recirculation mode 

Rear Window and Side Mirror Defogger

  • Activate read defogger

  • Wait for a few minutes 

  • Turn off the defogger manually

Side Window Defogger 

  • Adjust vents towards the side window

  • Adjust fan speed and temperature 

Understanding Primary vs. Secondary Defoggers

The Primary Defogger

The primary defogger is like an orchestra conductor, directing the flow of air. It collaborates closely with the vehicle's Air Conditioning (AC). This defogger draws fresh air, strips it of moisture, heats it, and then gracefully channels it to the front windshield. It's a dance of temperature and airflow, all in the name of clarity.

The Secondary Defogger

The secondary defogger is the tech geek of the duo. Instead of relying on airflow, it uses the principle of electric heating. Picture a network of tiny, almost invisible heating elements on your rear windshield. When activated, they warm up, melting away the pesky fog. It's like having a heated blanket but for your rear window.

How To Defog Windshields? 

  • Locate the Button: On your car's dashboard, find the button with a symbol that looks like wavy lines or a rectangle with lines inside. It is the defogger button.

  • Press the Button: Push the defogger button to activate the system. Some cars might have an indicator light that turns on when the defogger is active.

  • Choose Front or Rear: If your car has separate buttons for the front and rear defoggers, select the one you need. The front defogger usually uses the car's air system, while the rear often uses electric lines.

  • Adjust the Temperature: For the front defogger, set the car's temperature to warmer to clear fog faster in cold conditions. In warmer conditions, a cooler setting might be more effective.

  • Turn Off Air Recirculation: Ensure the air recirculation mode is off. It allows fresh air from outside to enter, which is more effective in clearing the fog.

  • Adjust Fan Speed: Increase the fan speed for a quicker defogging effect. Once the fog clears, you can reduce it to a comfortable level.

  • Check Duration: Some rear defoggers have a set duration and will turn off automatically after a certain period. If the fog hasn't cleared, you might need to press the button again.

  • Turn Off When Clear: Once your windows are clear, turn off the defogger to save energy and maintain a comfortable temperature inside the car.

Refer to your car's manual for specific instructions, as the defogger activation process might vary slightly between car models.

Using a Defogger With the AC

Your car's AC is a versatile tool. While its primary role might be to keep you cool, it's also a secret weapon against fog. You can turn your AC into a defogging powerhouse by adjusting its temperature and air circulation mode settings. It's about creating the perfect balance between the inside and outside temperatures.

Using a Defogger Without the AC 

For those cruising in vintage cars or facing a temperamental AC, despair not. The art of defogging has some old-school tricks up its sleeve:

  • The classic roll-down: Sometimes, the simplest solution is to let nature in. Rolling down your windows allows for a quick air exchange, reducing fog.

  • Circulation is key: Ensuring proper air movement inside the cabin without a working AC becomes crucial. It's all about letting the warm, moist air out and welcoming the fresh air in.

Seasonal Defogging: A Year-Round Guide

  • Chilly Winters: In the cold, your car becomes a warm refuge. But this warmth can lead to fogging. Turning off air recirculation and balancing the AC temperature can work wonders here. The defogger button becomes your best friend, ensuring clear views even on the frostiest days.

  • Summers: Surprisingly, summer can also bring fogging woes, especially when the inside of your car feels like an icebox compared to the sweltering outside. Here, increasing the AC temperature slightly, using the windshield wipers, or even a quick roll-down of the windows can clear things up in a jiffy.

Proactive Measures To Prevent Fogging

  • Silica Magic: Those tiny silica balls are moisture magnets, often found in new bags or shoeboxes. Please place them in a sock and let them work their magic in your car.

  • Shaving Foam Hack: A thin layer of shaving foam on your windscreen can act as a barrier, preventing moisture buildup. It's an unconventional trick that can make all the difference.

Maintenance and Care: Keeping Your Defogger in Top Shape

We often take our car's defogger for granted, only realizing its importance when it doesn't work as expected. Like any other part of your vehicle, the defogger needs regular attention. Here are some tips to ensure it remains in peak condition:

  • Regularly Clean Your Windshield: Dirt and grime can interfere with the defogger's efficiency. A clean windshield ensures better visibility and allows the defogger to work effectively.

  • Check the Electrical Connections: Ensure the rear defogger's electrical connections are secure. Loose or corroded connections can hinder its performance.

  • Ventilation Check: Ensure the car's vents, especially those near the windshield, aren't blocked. Regularly cleaning the vents can prevent dust accumulation, allowing for better airflow.


Driving is more than just a commute; it's an experience, a journey. Amidst the open road's thrill and the engine's hum, clear vision stands paramount. The defogger, a silent yet essential companion, ensures that no matter the weather, our view remains unclouded. As we navigate through changing seasons and diverse terrains, knowing that a guardian ensures our path remains clear is comforting. After all, the beauty of a journey lies not just in the destination but also in the clarity of the journey itself.

A defogger keeps you safe from hampered vision and, thus, prevents mishaps. Similarly, car insurance protects you against financial losses in case of mishaps. Explore ACKO to learn more about motor insurance and buy an insurance plan that suits your needs.

Frequently Asked Questions

Below are some of the frequently asked questions on Defogger in Car | Rear & Front Car Defogger | How to Use?


How does a defogger work in a car?

A defogger works by combating condensation. The front windshield uses the car's heating system to blow warm air, preventing moisture buildup. The rear defogger utilizes electrical heating elements (those thin lines on the back window) to heat the glass and evaporate moisture, ensuring a clear view.

Does the defogger use AC?

Yes, it can! While it might sound counterintuitive, the car's AC plays a crucial role in defogging. The air conditioner dries out the air inside the vehicle. Combining this dry air with the warm air from the car's heater becomes a powerful tool against fog. So, the next time you're using the defogger, remember that the AC isn't just for those hot summer days; it's also your ally against foggy windows.

What is the difference between defrost and defog in a car?

"Defrost" focuses on removing frost or ice from the exterior of the car's windows, especially during cold conditions. In contrast, "defog" is about clearing the moisture or condensation that forms on the interior of the windows. Defrost deals with the outside, while defog handles the inside. They often work in tandem to ensure you have a safe drive in foggy conditions. 

How long does it take for a defogger to clear the window?

The time taken to clear the car's window by your defogger will vary based on the temperature, humidity and the effectiveness of the defogging system. Typically, the defogger might take a few minutes to clear the window efficiently.  

Does defogger have an impact on a car's battery?

The rear defogger will consume electrical power. However, the impact on the battery is usually minimal during regular vehicle operation. In case the usage of a defogger is extensive, it might potentially drain the car's battery. 


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