What is Defogger in Cars?

  • Author :
  • TATA AIG Team
  • Published on :
  • 21/11/2023

In rainy and winter seasons, you must have faced the problem of water condensing on your car’s windscreen and side windows. It happens when the warm air inside your car comes into contact with the colder glass and turns into water droplets.

In colder regions, the problem gets even worse when ice accumulates on the glass. The resultant poor visibility may make it challenging for you to drive safely.

This is where the role of defoggers comes in. Defoggers in cars play an essential role in road safety by ensuring you get a clear view of the outside.

In this article, we will learn all about car windshield defoggers, their types and how to use them effectively. But let us first know why your car windows fog up.

Why Car Windows Fog Up?

There are a few reasons behind car windows fogging up. Temperature difference between your car’s interior and exterior is the most common cause. Water condenses on the colder surface of your car, usually glass, when there is a significant temperature difference.

Another reason why your car windows fog up is the outside humidity. If you live in places with high humidity, you may have experienced the problem.

It happens when the air outside your vehicle is saturated with water vapour. When it comes into contact with the colder glass, your windows may fog up blurring the view outside.

What is a Defogger in a Car?

A defogger is a device in cars that helps in the removal of condensed water droplets or fog from the front and rear windscreen, and side windows. It is also referred to as a “demister” or “defroster.”

Defogger is mainly used during rainy and winter seasons. Most cars usually have two types of defoggers- one for the front windshield and the other for the rear windshield.

Now let's understand how both types of defoggers differ from each other and why they are important for safe driving.

Types of Defoggers in Cars

Defoggers are designed for both the front and rear windshield of cars to ensure a clear front and rear view. However, their working mechanism differs. Here’s the difference between the two types of defoggers:

Front Defogger in Car

The front windshield offers you a view of the road in front while driving. You may land into big trouble if the front view of your car gets obstructed due to fog, rain or frost. The front defogger makes sure you always get a crystal-clear view of the road ahead while driving. Here’s how the front defogger for car windshield works.

The front defogger blows warm air onto the front windshield.

It uses your car’s Heating, Ventilation and Air Conditioning system (HVAC) to raise the glass temperature which helps prevent condensation.

When you activate the HVAC system, warm air is directed to vents placed at the base of the front windshield.

This warm air spreads over the entire surface of the glass and clears the condensation or fog on it.

Rear Defogger in Car

Besides the front view, the rear view also plays an important role in safe driving. A fogged-up rear windshield can make it difficult for you to see the vehicles behind you. It may also cause problems in making lane changes or reversing your car leading to collisions or accidents.

A car rear defogger thus plays an essential role in saving you from potential mishaps. Here’s how a rear car windshield defogger works.

The rear defogger in the car doesn't work on your car’s HVAC system.

Instead, it uses an electrical system to heat the windshield.

You can see it in the form of a grid of thin lines that are made of conductive material.

These lines get warm when electricity passes through them which helps in clearing of the fog or mist from the windshield.

How to Use a Car Defogger?

Using a defogger in the car is quite simple. While the features may vary depending on the make and model of your car, the basic functionality is the same. Here’s how you can use a car defogger:

Front defogger: To use the front defogger in the car, first start your car and activate the defogger. Now adjust the temperature and fan speed and turn off the air recirculation mode. Turn off the settings once the glass is clear.

Rear defogger: Activate the rear defogger and wait for some time until the moisture is cleared. Now turn off the defogger manually.

How to Defog Your Car’s Windshields?

Here’s a **Step-by-**Step process to use car windshield defogger:

Step 1: Locate the defogger button on your car’s dashboard. It has a symbol of a rectangle with lines inside or wavy lines.

Step 2: Activate the defogger in the car by pushing the button. In some cars, there is an indicator light that indicates activation of the defogger system.

Step 3: If your car is equipped with different buttons for the front and rear defogger, press the one you wish to activate.

As mentioned above, the front defogger uses your car’s heating system while the rear defogger uses the electrical system.

Step 4: You must now adjust the temperature based on the weather conditions. Adjust the temperature to warmer if the weather is cold.

This will help clear the fog more quickly. However, a cooler setting may suffice when the weather conditions are hot.

Step 5: When activating the front defogger, make sure your car’s air recirculation mode is turned off. This lets fresh air from the outside come in which helps in quick clearance of the fog.

Step 6: You must also adjust your fan speed. You can set it to maximum to make the defogging more effective. Once done, you can set it according to your comfort level.

Step 7: In some cars, rear defoggers work on a set duration. It means they automatically turn off after a period.

In such cases, you can press the button again if the fog doesn’t clear in the first instance.

Step 8: Once fog gets cleared from all the glass surfaces, switch off the defogger to keep an optimum temperature inside your car.

Note:** The defogger activation process may vary between different car models. So, make sure you read the instructions properly from your car’s manual

How Can You Prevent Fogging?

You can prevent fog or moisture build-up in your car by taking a few proactive measures. Here are a few hacks that can help keep your car free from fog and ensure a clear view at all times:

Keep silica gel pellets: You can keep silica gel pellets inside your car. They act as good moisture absorbers and help prevent fogging

Use shaving foam on the windshield: Another hack to prevent fogging and misting is to put a thin layer of shaving cream or foam on your car’s windshield. This helps in creating a barrier between the moisture particles and the glass surface.

Take shaving foam or cream and apply it on a dry towel to clean the interior of the windshields. To ensure the cream is not visible on the windshield, wipe the residual cream with another dry towel.

Use window cleaner that has ammonia: To clean your car’s glass components, choose a cleaner that has ammonia. You can also clean the inside of the windshield with it to prevent fogging.

Use fresh air mode in place of recirculation: Using your car’s air conditioner in fresh air mode can also prevent fogging. It ensures that air doesn’t recirculate inside your car.

The fresh air mode allows fresh air from outside to get in and regulates the temperature thus preventing fogging.

Open your car windows: A simple way of defogging your car’s windshields is to open your car windows. This lets the fresh air from outside come in and reduce the moisture in the car.

Keep your shoes dry: Water or snow may stick to your shoes during a snowfall or rainy season. Make sure you wipe off your shoes before entering your car. This can help reduce moisture and prevent fogging.

Maintenance of Car Defoggers

Like any other component of your car, a defogger for car windshields too requires regular maintenance. Here are a few ways through which you can ensure your car defoggers work efficiently all the time:

Ensure proper maintenance of the HVAC system: The HVAC system of your car plays an essential role in maintaining appropriate temperature. So, any malfunction in this system can lead to major temperature differences and cause fogging.

If your car’s windshield fogs up on turning on the defroster, it may be a sign that the HVAC system needs cleaning or repair.

Clean your windshield regularly: Dirt or filth accumulates on the windshield if not cleaned regularly. This can reduce the efficiency of the defogger.

Hence, it is important to keep your windshields clean all the time to ensure clear visibility after defogging.

Regularly check the electrical connections: Check the electrical connections to the rear defogger regularly. If the connections get loose or corroded, get them repaired to ensure proper functioning.

Check for proper ventilation: Blocked car vents can impact the effective working of the front defogger. So, clean them regularly to prevent dust accumulation and ensure better ventilation.

Wrapping Up

Driving comes with much responsibility. While driving, you are responsible for your safety as well as that of others on the road. Defoggers are crucial components in a car. They help provide a clear view of the road ahead and behind thus protecting you and others from any mishap.

Despite having all safety measures in place, it is important to buy car insurance to remain safe from unforeseen events on the road. Car insurance is an excellent tool to protect yourself from financial liabilities resulting from third-party and own losses.

While third-party car insurance covers damage or injuries to third parties, comprehensive car insurance can provide all-round safety to your car. It covers financial damages to your car caused due to theft, accidents, natural disasters, vandalism, etc.

Now that you know the importance of car insurance, make sure you buy the best suitable policy for your prized possession.

Tata AIG provides a range of car insurance policies that are designed keeping in mind the potential mishaps in today's time. Get a quote on our website, compare car insurance online and pick the best four-wheeler insurance policy today.


How does defogger work in a car?

A defogger in the car helps prevent condensation. It uses the car's heating, ventilation and AC system to blow warm air on the front windshield and clear the fog or mist. For the rear windshield, it uses an electrical system to heat the thin lines on its surface to clear off moisture.

What are the benefits of a defogger?

A defogger provides you with a clear view of the road ahead and behind so that you can drive safely. It clears off all the fog or condensed water instantly and saves you from potential accidents or collisions.

Does the defogger use AC?

Yes, a defogger can use AC. Your car’s air conditioning system plays an important role in defogging by drying out the air inside your car. When this dry air mixes with the warm air from the heater, the fog on the glass surfaces vanishes.

How do I start a defogger?

Here’s how you can start a defogger:

Press the defog button

Make sure the Recirculation button is turned off

Press the sync button

Now set the fan to the maximum setting

Set the temperature to “High” in the automatic system and “Full Hot” in a manual system

Turn the AC on when defogging

Once the view is clear, turn off the settings

What is the difference between defog and defrost?

To defog is to clear the fog and condensation from the inside of the car’s windshields and windows. On the other hand, defrost is to remove ice or frost from the outside of the car’s glass surfaces. Defrosting is done in colder regions.

Does defogger affect a car’s battery?

The rear windshield defogger works on electrical power. While it has minimum impact on your car battery during normal operation, a defogger can drain the battery when used extensively.

How much time does a defogger take to clear all the windows?

While a defogger usually takes a few minutes to clear all the windows and windshields, the time may depend on the humidity, temperature and the efficiency of your car’s defogging system.

Does car anti-fog spray work?

Yes, car anti-fog sprays are quite effective if you use them correctly. They consist of chemicals that reduce the surface tension of water droplets. This prevents them from creating a layer of mist on the glass surface.

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