Defogger in a car: How to defog car windows in the rain

Team AckodriveJun 6, 2022

Driving during the monsoon season can be a refreshing experience. However, it brings in additional challenges in the form of low visibility due to rain. The challenge is compounded when your car’s windshield gets fogged up due to the cold weather. It obstructs your vision and can be a dangerous scenario. But you can quickly solve the problem with the help of a defogger in the car. Read on as we discuss how to defog car windows in the rain.

Defogger in a Car

What is a defogger in a car, and how does it work?

Before looking into the functioning of a defogger in a car, let's understand the reason behind fogging of car windshields and windows. Fogging is a phenomenon that occurs when warm air comes in contact with a cold surface. Here, the cold surface is the windscreen of a vehicle. It is also called condensation, as it forms tiny water droplets on the surface of the windshield.

Now, coming to the defogger, it is a device that helps remove the condensed water droplets from the windshields/windows. It also helps to improve visibility, especially when it is raining. The device is also called demister or defroster.

Defoggers are classified into two categories based on their working mechanism: primary and secondary defogger. The below points explain the working principle of a primary defogger.

  • A primary defroster in a car operates with the help of the vehicle's Air Conditioning (AC) and hot air.

  • The vehicle's AC draws fresh air from the atmosphere and dehumidifies the air.

  • Next, the dehumidified air passes through the heater core, and hot air comes out.

  • The hot air is channelled through the vents to reach the desired location, such as the front windshield.

  • Generally, a primary defroster in a car is used to defrost the front windshield.

  • This type of defogger works in conjunction with the car's AC unit.

  • Glance through the below points to understand the working of a secondary defroster in a car.

  • A secondary defogger works on the principle of electric heating.

  • A heating element is pasted on the glass surface to help defog the windshield.

  • When you activate the system, an electric current passes through the filaments of the heating material, and it produces heat.

  • Hence, the heat melts the condensed water droplets on the glass surface.

  • A secondary defogger is generally used on rear windshields.

  • Some luxury vehicles may also use this system to defog the outside rearview mirrors.

How to use a defogger in a car to demist windshield

A defogger or defroster in a car is one of the most common features you find in a vehicle. It helps you to defog the front windshield, windows and rear windshield. Activating the defogger function in a car is as simple as pressing a button. The below points explain how to use a defogger in a car.

  • If you observe your car's dashboard, you may find a button with a sign resembling three squiggly arrows. 

  • You can press the button once to activate the defrost function, and the sign illuminates when the defrost function is on.

  • When you press the defogger button, hot air is channelled towards the windshield to clear the fog. 

  • You can press the same button once more to deactivate the defogger.

  • Some cars may have two defogger buttons, one for the front windshield and the other for the rear.

How to defog car windows in rain with AC

Now, you may be thinking about how the vehicle’s AC can help defog car windows when it blows cold air? In some situations like cold weather during the monsoon season, the AC can come in handy to clear out the fog. The below points explain how you can use the car’s air conditioning system to demist the windshields and windows.

  • Switch on the AC as it helps remove moisture from the air. The lesser the moisture, the less the chance of fogging.

  • Reduce the AC temperature to match the outside temperature. However, this may not be an ideal option if the outside temperature is too low.

  • You can turn off the air recirculation function to allow the AC to draw some fresh air inside the car.

  • You can also turn on the heater to quickly clear the fog.

  • Lastly, you can also turn on the defogger as it blows hot air into the glass surface and quickly clears the fog.

How to demist car windows in rain without AC

Generally, all modern cars are equipped with AC. If you drive an old car without AC or your car’s AC is not functioning, defogging the windows and windshield may be challenging. Another way to defrost car windows is by using the defogger function. We have already explained how to use a defogger in a car. But what if both AC and defogger in a car are not working correctly? It would be best to find an effective way to clear the fog without AC and defogger.

The effective way to clear the fog without AC is to roll down the windows. That way, the air with less moisture enters the cabin and helps clear the mist on the windows. However, it may not be ideal to roll down the windows when it’s raining heavily.

Without an air circulation system inside the cabin, it becomes difficult to clear the fog on the glass surfaces. The only solution is allowing the warm and moist air to escape out of the cabin. And for that, you can roll down the windows.

Steps to defog rear window of a car

A clear rear windshield is necessary for a driver to observe the traffic behind the vehicle through the inside rearview mirror. A fogged up rear window can hamper safety. Hence, defogging the rear window is as essential as defrosting the front windshield. You can follow the below points to defog your car's rear window.

  • If your car has a rear defogger button, press it to clear the condensed water droplets from the rear windshield.

  • You can switch on AC to reduce the moisture content in the air.

  • Turning on the heater can also defog the rear window.

  • Open the windows to allow fresh air inside the cabin, and you will see the fog disappearing from the rear windshield.

How to remove fog from car glass during winter

The outside temperature will be colder during winters than the car's cabin temperature. Hence, when the warm air inside the car comes in contact with the cold glass surface, it fogs up due to condensation. However, by following the below points, you can demist the windows during winter.

  • Turn off the air recirculation function in your car. You may find a button with a sign of an arrow inside a car, and that's for turning on air recirculation. By turning it off, you allow the fresh air to enter the cabin, and it helps reduce the inside temperature. The fog will disappear from the windshield/windows when the temperature balances out.

  • Lower the AC temperature to match the cabin's temperature and the atmosphere. It may be a problem if the outside temperature is too low. However, the fogged windows and windshields should be clear once the cabin temperature reduces.

  • Turn on the defogger function to quickly defrost the windows. It blows hot air into the windshield and quickly clears the fog. It is one of the effective ways to defog the car windows during winter.

How to defog windshield in the summer humidity

You might be wrong if you thought fogging occurs only during winters and monsoons. Your car's windshield may fog up in the hot and humid weather, provided your cabin temperature is cooler than the outside temperature. 

Generally, a car's AC is always on during summers, and it lowers the cabin temperature. When the hot air on the outside touches the cold glass surface, it fogs up the windshield. However, the phenomenon occurs on the outer surface of the glass. Hence, it's easy to clear the fog.

You can follow the points below to quickly clear fog during hot weather.

  • Increase AC temperature: Increase the AC temperature to raise the temperature inside the cabin. That way, the outside and inside temperature will be balanced, and it will immediately clear the fog. But it may not be an ideal solution if the outside temperature is too high.

  • Switch on windshield wipers: Another easiest way to get rid of the fog is by switching on the windshield wipers. As mentioned earlier, the fogging up happens on the outside glass surface. Hence, the wipers can quickly clear the mist.

  • Roll down the windows: One more way of demisting is by rolling down the windows. Allow the warm outside air to enter the cabin to match the outside and inside temperature. It will automatically remove any fog on the windshields or windows.

Also, read: How to Change the Wiper Blades of Your Car on Your Own?

How to defrost windshield while driving

There are no unique methods to clear windshield fog while driving. You can follow the above-mentioned points to defrost the windshield while on the move. However, make sure that you don’t get distracted while driving. It would be ideal if you park your car on the side of the road and then make adjustments inside the vehicle to clear the fog.

The most convenient way to clear the fog while driving is by pressing the defogger button. It’s easily reachable to the driver, and it does not distract the person behind the wheel. Always avoid wiping the windshield with a cloth when you are driving, as you can easily lose your sight on the road.

How to prevent car windows from fogging up

Prevention is better than cure. So, what if you could prevent the glass surfaces from fogging up? Yes, there are some tricks to prevent the windshield from fogging up, and some of them are listed below.

  • Silica balls are good for moisture absorption. They are used to keep food and other products moisture-free.

  • You can fill silica balls in a sock and place them inside the car. It will absorb the moisture in the air and prevent fogging up of windows.

  • Another way to avoid fogging up is by applying shaving foam on the windscreen.

  • Spread the shaving foam across the glass surface and let it settle for a couple of minutes.

  • Next, you can wipe the residual foam using a clean cloth. It results in a protective layer over the windshield that prevents the moisture from collecting on the glass surface.

Frequently asked questions

Here are a few common queries and answers related to the defogger in the car.

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What is the use of a defogger in a car?

A defogger is necessary to clear the fog/mist from the windshield quickly. It improves visibility during cold weather when fog is a common phenomenon. It is a system that blows hot air into the windshield and quickly removes the water droplets accumulated on the glass surface.

How do I turn on the defogger in my car?

You can press the defogger/defrost button to switch on the system. Look for a button with three squiggly arrows, press it once to turn on the defogger, and press it again to switch off the system.

Is a rear defogger necessary for a car?

A rear defogger is essential for a car from a safety point of view. However, one can manage to drive safely without the rear defogging system. That being said, all modern cars do come with a rear defogger. So, you may find it on almost all vehicles in the market.

What is the reason for fogging up car windows from the inside?

If the inside temperature is warmer than the outside temperature, fogging up occurs on the inside glass surface. That’s because when the hot air inside the car touches the cold glass surface, it attracts moisture and fogs up.

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