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I have a second hand car with an old slider to switch from left to right, with the same icons 1, 2 as in the picture below. But I do not understand it well.

enter image description here

Often when I am driving, my car windows become like mist (like the 'before' section):

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How can I get rid of the mist, so that I have clear glass while driving?

enter image description here

  • that is not the important control. you need to find defog mode. post a better pic of all the controls and say what make and model – agentp Oct 18 '17 at 11:09
  • i.imgur.com/7hKpWWv.png – YumYumYum Oct 18 '17 at 11:29
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    you have the right knob on defog. fan (center) should be high. note with no ac the defog will not work very well until the engine has warmed up – agentp Oct 18 '17 at 11:36
  • By no ways am I an expert of car glasses, just dropped in to offer you something that worked for me. You could have heard of this, but rubbing your window with shaving cream or soap, then wiping it clean with a dry towel, prevents it from fogging up. It does not hamper your view at all and unless you rub it with your hands or something, does not disappear for a long time. I know this is about the car features and all, so if this is not appropriate for this community, I will take it down. :) – C. Miles Oct 18 '17 at 13:33
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In the two pictures/icons you provide the arrow is intended to indicate the flow of air with regards to the cabin. Where the arrow is coming in from outside the car allows air from outside the vehicle in through the HVAC vents. The circular (ish) arrow indicates that the air already inside the cabin is being recycled through the HVAC system and put out the vents.

If you are looking to avoid misting on the windows then you need to consider where the air is dryer. Given the fact that humans generally breathe out relatively warm, humid air leaving it on the recirculating setting will cause the cabin to fog up unless the HVAC system reduces the humidity of air passing through it. It's common for most modern air-conditioning systems to do this as part of cooling the air so in some cases it's better to have it on the re-circulation setting and let the AC dry it out for you.

Obviously if your vehicle doesn't have AC then it's pretty much always going to be better to have it set to allow fresh air in to avoid misting.

  • i.imgur.com/MehIXHZ.png - What are those 3 arrow control does? can you help to understand. – YumYumYum Oct 18 '17 at 11:37
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    I have mine set to point 1 pretty much all the time so you should be fine to do the same – motosubatsu Oct 18 '17 at 11:46
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    the push button with up arrows is your rear window defrost – agentp Oct 18 '17 at 11:49
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    The button (top left) is the re-demister, it controls a fine electric heating element in the rear window which you can turn on to demist that. The large dial is used to direct which interior vents are blowing air from the HVAC. Far right position directs it at the windscreen, top is directed to the footwells and I'd imagine (although I cant see it) that the far left is for the main cabin vents. The sliding knob is the recirculation control you asked about in the main question. – motosubatsu Oct 18 '17 at 11:50
  • Whilst the AC is cooling the air, fogging of the inside of the window surfaces is never an issue. That only happens when the panes are colder than the air inside the car. I suppose you could get fog on the outside surfaces when driving with fridge-like AC in a tropical climate, but in that case the circulation settings won't make any difference about it... (They would, however, make a big difference on fuel consumption.) – leftaroundabout Oct 18 '17 at 14:10
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First, you need to know what each does. #1 allows Fresh air from outside the vehicle. #2 is Recirculates air already inside the vehicle.

Unless you are running the AC, you should have the selector to #1. This will help reduce the "misting" effect you are seeing.

Selection #2 recirculates air within the vehicle. This is helpful during hot days when the AC is running, as it recirculates the already cold air. During colder weather, this setting typically causes the windows to fog up, or "mist".

The owner manual for my car states this;

If you select RECIRCULATION while in the VENT, BI-LEVEL or FLOOR modes, humid air can recirculate inside the vehicle and allow moisture to form on the windows. If this happens, either press the A/C button to on or select DEFROST or the DEFOG modes.

  • i.imgur.com/MehIXHZ.png - What is DEFROST or DEFOG button here? is it the button first arrow or second arrow from top? – YumYumYum Oct 18 '17 at 11:44
  • OK - 1) i am not using the AC (Aircondition just after starting my car). 2) So i put my "SLIDER" to the left in your reference "SLIDER" = #1 or #2. On left means #1 and on right means #2. 3) What about the 2 other arrow settings? – YumYumYum Oct 18 '17 at 11:48
  • You need to read your vehicles owner's manual. The symbols used are listed for you to be able to easily know what they are. In the picture, the right dial is set to defrost the windscreen. The bottom slider needs to be moved to the left for fresh air. The other arrow is pointing to the rear window defroster. – CharlieRB Oct 18 '17 at 11:48
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    You have given us no vehcile specific information. If you add that to the question, maybe we can give you more direct answers. – CharlieRB Oct 18 '17 at 11:52
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    Mitsubitshi carisma 1998 model - here they use wrong pictures mitshelp.com/micont-323.html – YumYumYum Oct 18 '17 at 11:52
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Fog on the windshield happens when there is warm, moist air inside the car and a cold windshield (chilled by the cold, dry air outside). So when using your ventilation system to de-fog your windshield, you want to do three things:

  1. Blow dry air over the windshield, to absorb the condensation from it
  2. Heat the windshield, so that the water evaporates into the cabin and further condensation stops
  3. Replace the moist air inside the cabin with dry air from outside

Therefore, the proper ventilation settings are:

  • Air blowing over the windshield at maximum fan speed (the "round" windshield icon)
  • Heater on, to help heat the windshield
  • Air coming from outside (setting #1 in your picture), since it's drier than the inside air, and
  • If available, the A/C activated, to dry out the air. (Yes, you're using both the heater and the air conditioner. The heater will win, but the air will be drier than with the A/C off.)
  • If necessary, the windows opened, to reduce humidity. (Yes, you're letting the hot air out, but you're still heating the windshield, and you're getting rid of humidity inside the cabin.)

A/C on, heater on, recirculation off, windows open. Your gas mileage won't be great, but at least you'll be able to see.

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Starting left to right, the controls you want to use are:

  1. Temperature: If you're somewhere cold, set this all the way cold at first. Reason is the heater will cool the engine while still blowing cold air until the engine gets hot, which means it literally takes longer to get any warm air.
  2. Slider: Put this all the way left -- that setting means 'draw in air from the outside and do not re-circulate it'
  3. Right control knob: You have it in the correct position, windshield vent.

Other options that can help: Roll down your windows, start the car & let it idle, then come back in a few minutes when it's at running temperature. The open windows will let most any moisture evaporate. You can do the above procedure with hot air too, once the engine is warm, but I've found it sometimes makes the problem worse for 10-20 seconds before starting to clear up the windshield.

I believe there are water repelling products that provide a thin hydrophobic film on the windows, greatly resisting fogging as well, but I haven't tried them myself

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TLDR: Never use recirc (position 2). The only time to use it is to squeeze extra performance out of your air conditioning. And A/C is very effective at clearing fog, even with heat too!

You need to know how to defog windows

Air has water in it. Windows fog over when the air is very humid.

If it's raining, most likely outside air is at 100% of its capacity to hold water. Your car is taking that in. Also, you are adding humidity to the car from your breath, sweat and wet clothes.

Warm air can hold more water. So if you run your heater, it will reduce fogging. Of course that may be no fun on a 30C night.

Use the air conditioning

The air conditioner makes the air quite cold. Remember, cold air can't hold nearly as much water, so the water falls out! That's how dehumidifiers work.

If you run A/C with the heat temperature high, the car will re-heat the air conditioned air. This will make it very, very dry.

If it's cold out, turn on the A/C and set max heat. This will defog the car in a few seconds.

If it's too cold out (below freezing) the A/C may not be able to run at all. The Freon system works fantastic at low temperatures, but the evaporator core will tend to ice up. Recirculation can help slow that down.

To recirculate, or not?

That lever decides whether to draw fresh air from outside the car (position 1), or whether to recirculate air already inside the car (position 2).

Generally you want fresh air most of the time -- for many reasons. If you don't have A/C, recirc is nearly useless. I never use it.

If you are not using A/C and simply using the heater to dehumidify, you need fresh air, otherwise your own humidity will add to the humidity already in the car and fog you up.

If you are using A/C to dehumidify the air, it helps to recirculate, because the air inside will be drier from already having been through the A/C.

  • I disagree with never using recirc. The recirc mode is useful when driving behind a diesel vehicle emitting clouds of black smoke. – juhist Aug 5 at 17:05
  • I turn the fan off at that point. Recirc is intentionally not 100%. – Harper - Reinstate Monica Aug 5 at 17:57

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