Not many things irritate motorists more quickly than when their windshields fog up. It's one thing if you can clearly see the road ahead, but suddenly your windshield gets all foggy and begins raining down on you at the same time. Your first reaction is likely to turn on the heat, since most motorists believe that windshield fog occurs only in cold weather.
However, as reported by some automakers, the fastest remedy may be flipping the switch for air conditioning, which many motorists resist during cold weather.
While this may seem counterintuitive, automakers insist that it's true.
In particular, Mazda USA says that fog on the windows will clear up better when the air conditioner works. Likewise, the owner's manual by Chevrolet recommends turning on the A/C and increasing the speed of the fan while defogging. According to the manuals of older Toyotas, warm air with low humidity is the key to quick results.
Why is that? Actually, it is quite simple: fog appears due to the condensation of moisture present in the cabin air on the cold windshield. The combination of warm air and the A/C's drying of the air can prevent moisture from forming on the windshield's cold surface. Therefore, it makes sense to combine both options.
Based on the guidelines mentioned in the owner’s manuals from Toyota, the use of outside air in this case would be more appropriate because the content of moisture in fresh air is lower than in already moist interior air. It will increase as passengers breathe, damp shoes are placed on floor mats, or water drips into the cabin due to rain.
By using fresh air from the outside, drivers will get rid of this additional moisture rather than circulate it all the time inside their vehicles. Modern cars switch from recirculation to outside air automatically when drivers turn on the windshield defrosting. Moreover, an air conditioner in such a case turns on automatically, unlike the way it acts normally under cool conditions, which can be puzzling.
However, it can be explained by the fact that cars try to produce the fastest warm and dry airflow.
As stated in Mazda Owner Digital Info about their cars' climate control systems, using air conditioning helps minimize moisture inside the car, making it easier to see during damp weather conditions.
It's important to remember that it isn't just the heater that eliminates the fog. Rather, it is a two-way process, where the car has to both warm the surface of the glass and dry out the air being blown through it. Failure to execute any one step may result in prolonged fog.
It also explains the phenomenon of windows becoming fogged even further when drivers turn on the heater without dehumidifying the interior.
The next time your windshield turns into a foggy mess, the easiest answer might not just be increasing the temperature, but the combination of warmer air and a lesser-known air conditioner that dries out the interior of the car.
However, as reported by some automakers, the fastest remedy may be flipping the switch for air conditioning, which many motorists resist during cold weather.
While this may seem counterintuitive, automakers insist that it's true.
Why the A/C button helps even in cold weather
One important reason why drivers prefer to go without their air conditioners when it is foggy outside is that people tend to believe that the primary function of their A/C is to cool down the passenger compartment. However, as one should know, an air conditioner removes not only the heat but also the moisture from the air.In particular, Mazda USA says that fog on the windows will clear up better when the air conditioner works. Likewise, the owner's manual by Chevrolet recommends turning on the A/C and increasing the speed of the fan while defogging. According to the manuals of older Toyotas, warm air with low humidity is the key to quick results.
Why is that? Actually, it is quite simple: fog appears due to the condensation of moisture present in the cabin air on the cold windshield. The combination of warm air and the A/C's drying of the air can prevent moisture from forming on the windshield's cold surface. Therefore, it makes sense to combine both options.
Why outside air matters more than recirculation
A further misconception is switching on recirculation in the climate system. Although recirculated air can cool or warm the cabin efficiently while driving, it can also worsen windshield fogging.Based on the guidelines mentioned in the owner’s manuals from Toyota, the use of outside air in this case would be more appropriate because the content of moisture in fresh air is lower than in already moist interior air. It will increase as passengers breathe, damp shoes are placed on floor mats, or water drips into the cabin due to rain.
By using fresh air from the outside, drivers will get rid of this additional moisture rather than circulate it all the time inside their vehicles. Modern cars switch from recirculation to outside air automatically when drivers turn on the windshield defrosting. Moreover, an air conditioner in such a case turns on automatically, unlike the way it acts normally under cool conditions, which can be puzzling.
However, it can be explained by the fact that cars try to produce the fastest warm and dry airflow.
Image Credit: Gemini| A driver in a car struggling with a foggy windshield
What drivers should do when the windshield fogs?
In general, most auto manufacturers suggest almost identical steps to get rid of misted glass quickly:- Activate defroster/defogger mode
- Adjust the temperature to warm
- Activate air conditioning
- Draw in fresh air rather than use recirculation mode
- Raise the fan speed so the flow of air is strong enough to blow over the windshield
As stated in Mazda Owner Digital Info about their cars' climate control systems, using air conditioning helps minimize moisture inside the car, making it easier to see during damp weather conditions.
Why this trick feels more useful once you understand it
A big reason why this suggestion works so well is that it completely alters the perspective that many drivers have on climate control. Dashboard controls are often thought to be random and overly complex when drivers face unfavorable weather conditions. However, when one realizes that the A/C acts like a dehumidifier, it all becomes a lot easier to comprehend.It's important to remember that it isn't just the heater that eliminates the fog. Rather, it is a two-way process, where the car has to both warm the surface of the glass and dry out the air being blown through it. Failure to execute any one step may result in prolonged fog.
It also explains the phenomenon of windows becoming fogged even further when drivers turn on the heater without dehumidifying the interior.
When fogging could point to another issue
Fogging on your windshield now and then is completely normal when it is raining, during cold mornings, or when there is high humidity. But excessive or continuous fogging might point towards some other problem with your car. It has been suggested by certain car manufacturers and mechanics that a blocked cabin filter, a leak in the vehicle, or moisture being trapped in the floor mats may be reasons why you have trouble with the foggy windshield. But if your problem is simply a foggy windshield due to high humidity, it might require only a few seconds to solve.The next time your windshield turns into a foggy mess, the easiest answer might not just be increasing the temperature, but the combination of warmer air and a lesser-known air conditioner that dries out the interior of the car.
