Preventing fog without AC

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Usually, it seems, when running the cold air when the weather is damp and about 70 degrees Fahrenheit that windows will fog. Now usually you could roll the window, but if it is raining it could let water in and if you do close the windows after intaking some rain- it seems the fog could get worse.


Is the only wait to fix fogged up windows ( or prevent them), without the use of compressed cold air air conditioning t use HEAT, thus sweating bullets? Or is there a way to keep in relative comfort and have good visivility?


Im mostly talking 70F and above....to say 90F....
thanks
 
First step is to clean windows well. It doesn't solve condensation issues and temporary erasure mismatch, but cleaner windows "fog" less than dirty ones.

From there you need to understand where is the cold/hot side and where the humidity is coming from.
 
I've recently used Rain-X anti-fog spray (bought at Walmart). I'm not really impressed with it, as it leaves a heavy haze that is really difficult to remove, even with repeated wiping with a clean cloth. There does seem to be less window fog than usual though.
 
I've driven cars without A/C (no AC installed) and was a PITA to keep them fog free. You were always running the defrost or heat at full blast and/or opening a window. Best to spend the .01 MPG penalty and jet the defrost run the AC.
 
Any coating won't prevent moisture from condensing, but it may allow you to see through it. And the rub is the moisture helps wash away the coating, so you have to reapply it.

That said there are nice anti-fog windscreens for motorcycle helmets, where fog is a real problem and A/C is not an option. Eventually the moisture build up is so severe you have to use a finger to wipe the inside of the shield.
 
Originally Posted By: gman2304
Also make sure your HVAC is set on fresh outside air, rather than recirculated air.


You want to cut humidity, probably a better shot of that with interior air when it's raining out.

If you run heat only, the dewpoint doesn't change, so it'll be around 70 degrees, which is clammy.
 
weird, my experience from Toyotas and Hondas have been good in the defogging department, I put it on cold or middle of the climate control gauge setting and make sure to NOT circulate the air and it doesn't fog for me...the drive and passenger vent are always facing their respective windows to prevent any fogging there.

I never ever use AC to defog, I have done that maybe twice in my whole driving experience, and I have easily driven over a million miles in 11 years since i got my license.
 
I have a a KIA Optima and a Honda Civic. The Optima gets rid of the fogged windows quickly but the Civic is much more difficult. It is hard to find the balance between frosting up the windows with the AC on and removing the fog.
 
If you run your HVAC on recirculate, in a closed vehicle, you're recirculating your exhaled air as well as your body heat and the windows will fog in just a few minutes. Even with a window slightly open, without setting the temp controls at about mid level and running the A/C compressor intermittently, and with your HVAC set on fresh air in the temps the OP described, it will be difficult to keep the windows clear.
 
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Using AC is the simplest and most effective method of defogging the windows. Most cars made since early 2000s automatically turn on the compressor when window defrost or floor setting is selected. I used to worry about it, but not anymore because it has a nice side benefit. It ensures that the AC is used during cold months, thus lubricates the whole system, including numerous packings. In places like Canada the AC may not be used for 8 months or more out of 12, so having it turn on with defrost setting is nice from system durability point of view.

However, I noticed that ever since manufacturers started to design their HVAC systems with AC being its integral part to function properly, they are much less efficient at keeping the windows fog free if one tries to avoid cycling the compressor. My Mazda 3 is pretty bad at it when compared to my previous 90s cars.
 
Originally Posted By: 01_celica_gt

I never ever use AC to defog, I have done that maybe twice in my whole driving experience, and I have easily driven over a million miles in 11 years since i got my license.

When you hit the front defog button, most cars built in the last 20-30 years automatically cycle the AC if it's warm enough. Many don't indicate it.
 
The Focus still has a mechanical control to pick your outlets, so I can put the control to just beside defrost setting allowing air through the defrost vents, but without running the AC compressor. The CRV is all push buttons so it runs the AC all winter when on defrost...
The other thing you can look for is water under the carpets or in the trunk. That's the only time I've really had bad fogging.
 
The fogging issue seems to be vehicle dependent. In humid weather around 55 - 65 degrees, the A/C is basically a requirement to keep the windshield from fogging in my Jeep, especially with passengers. If the A/C isn't working, it's defrost vents, fan on max and try not to breathe towards the windshield.

I'm not really sure why some vehicles are more prone to this than others though.
 
had a '57 belair. of course it didn't have a/c. rarely ever had issues with fog. of course, you'd get it toasty-warm inside and everyone wanted to nap during the drive home.
 
Originally Posted By: itguy08
Originally Posted By: 01_celica_gt

I never ever use AC to defog, I have done that maybe twice in my whole driving experience, and I have easily driven over a million miles in 11 years since i got my license.

When you hit the front defog button, most cars built in the last 20-30 years automatically cycle the AC if it's warm enough. Many don't indicate it.
I realize that, but I never mentioned that I hit the defog button, where are you making that assumption from?
 
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OP is in Mississippi, where the concrete sweats this time of year.

I drove there for a few years in an old car without air conditioning, and I can't remember this being a problem. My windows do fog up on damp days in VA, warm and cool, but air conditioning takes care of it.

As somebody mentioned, is your A/C on fresh instead of recirculate? Do the windows keep fogging after the system has run for awhile to dry the interior air? I'm stumped otherwise.
 
On all my GM cars, putting the controls to blow air onto feet diverts a little trickle of air to the windshield. Sometimes it's enough in colder weather. When it's rainy and cool, running the defroster on low speed constantly is the only way to keep windows fog-free.
 
Exhaling on a cold window will cause it to fog up. So roll down the window. Shave Cream applied to the window also helps.
 
Originally Posted By: 01_celica_gt

When you hit the front defog button, most cars built in the last 20-30 years automatically cycle the AC if it's warm enough. Many don't indicate it.
I realize that, but I never mentioned that I hit the defog button, where are you making that assumption from?[/quote]

The vast majority of people defog with the defog button. It's the quickest way to defog a windshield and the side windows in cars with vents for that purpose. The rear is defogged with the rear defrost/defog button.

Being from St. Louis where it snows, that is also the quickest way to clear a snowy or icy windshield.
 
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