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Old 07-12-2003, 01:15 AM   #1
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Member#: 10267
Join Date: Sep 2001
Location: Houston, TX
2001 Impreza RS

Default windshield fogging problems

I have what may or may not be an issue with my car (GC8 RS). My windshield is always fogging up. day and night. blowing the defrost on it will away the fog for a while, but then it comes right back. I seem to have had this problem for a while,. It may be related to the summer, but I seem to remember having this problem before then. New windshield (old one + flying rocks = blarg) didn't seem to change anyting.
It's getting to be a safety issue sometimes, too. mega glare...
I drive my girlfriend's car sometimes, and hers never seems to fog up at all. So it's not just my body funk. or nasty houston weather.
Does it sound like I have some ambient humidity in my car, or a dirty in car air cleaner element, or soehting else? What about those products I see in the store that are suppoed to eleminate glare and fogging. any reports?



ps. how do you pop off the front cabin light cover? one fo the light bulbs seems to have burnt out already, or it has a short (boo). It's annoying not having my driver's side reading light when I'm looking for something under my seat...
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Old 07-12-2003, 07:34 AM   #2
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Did you set the air conditioning to "Fresh air"?
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Old 07-12-2003, 10:29 AM   #3
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2001 Impreza RS


no, is it supposed to be?
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Old 07-12-2003, 12:09 PM   #4
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'02 rex


If you put it on fresh air it'll take most of the moisture out of the air and circulate fresh air in. Put it on defrost and open the fresh air vent and drive. Should take care of it. hope this helps
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Old 07-12-2003, 02:51 PM   #5
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Default My two cents

I am a huge advocate of rain-x on all exterior windows and fog-x inside. I'd like to shake the hand of the person who invented this stuff! Its awesome! Don't know how I ever got along without it or how everyone else gets along without it now.... I even use the fog-x for my bathroom mirror in the house - works perfect!!
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Old 07-12-2003, 03:44 PM   #6
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1998 Legacy Wagon
Spruce Pearl


I agree

I had a really scary thing happen to me this past winter. It was on a day that was below freezing, but the roads were very wet. I got behind some cars that were throwing up a lot of water (I think this is what caused it) and suddenly my windshield totally fogged up. This normally wouldn't be too big of a problem, but it froze over almost instantly. The entire surface on the inside of my windshield and front two windows was covered in frost!! And I was on the freeway, too
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Old 07-16-2003, 12:44 AM   #7
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Location: Northern NJ
2003 Wrx Wagon

Default foggin windows

I have tried the fog-x, and have has some sucess, but not that great. I have had more sucess in just using dish soap very diluted put it on the windshield and then let it dry and whipe it down. that worked the best for me.

Just my $.02
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Old 07-16-2003, 06:05 AM   #8
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Another possibility is goopy chemicals called plasticizers which slowly evaporate from many of the plastics in new cars (and also from slick dash treatments like ArmorAll). They condense on the insides of the car's windows, making a very thin oily haze over time. You should be able to remove it by using window cleaner on the inside of the car's windows.
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Old 07-16-2003, 11:29 AM   #9
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1998 Impreza 2.5RS

Default cabin filter

1. Make sure you set your HVAC to outside air, not recirculate.
2. If you have a cabin filter, make sure it is changed on time.
3. Clean the inside of your windshield with Windex (or similar) to remove the oily film that accumulates there.
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Old 08-28-2003, 07:34 PM   #10
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Default Fogging up

The problem you describe has always existed since the advent of A/C in automobiles, but became much more of a nuisence with the advent of non-freon refrigerants that have a much lower cooling efficiency than freon.

To make up for the loss in efficiency the A/C evaporator had to be redesigned. As a result modern day A/C evaporators can act very much like a sponge. In order to increase efficiency the evaporator had to become much more complex, more metal vanes, cooling surfaces exposed to the airflow, all stacked into a very tight space under your dash.

In simple terms, a SPONGE.

When you park your car for the evening after a humid day of heavy A/C use, the evaporator will likely be saturated, throughly CHOKED, with moisture. During the day as the system continued to operate the condensed mositure would accumulate into droplets large enough for gravity to overcome viscosity and then run out the drain tube provided for tha very purpose.

But not your car is sitting there with a very thin firm of moisture covering about 10,000 square inches (92 Lexus LS400) of cooling vane surface.

If you park inside it will help tremendously if you can lower all of the windows during the night. Then, unless the garage is quite cool, the thin film will evaporate into the local atmosphere and much of it will then end up outside the vehicle.

Another aspect of this that you might take serious note of is the fact that during the winter when outside temperatures decline below freezing the vehicle's A/C cooling capability will become totally and completely inoperable. Many modern day systems actually disable the A/C compressor altogether when the outside temperature declines to 35F and below.

It's cold outside, so who cares, you say.

Well, you do care.

Many, if not most, modern day automatic A/C systems will operate the A/C system all year around in order to more closely regulate the cabin temperature and humidity.

But even if that is not the case almost ALL systems will automatically activate the A/C when the defrost/defog/demist mode is activated.

So there are two things to remember.

First, if you happen to use the A/C for defogging during fairly cool weather then when you exit that mode the thin film of moisture left will oftentimes act like a MOISTURE BOMB. Shortly after you deactivate defog mode that thin film of mositure will begin to evaporate back into the incoming airstream in which case you might end up with higher cabin humidity, and possibly a more severely fogged windshield, than before the first use of the defog function.

Second, and this is for those of you with automatic A/C systems or climate control, as you drive your vehicle into an area of declining temperatures the A/C control system may, spontaneously and without any indication to you whatsoever, disable the A/C compressor completely due to outside temperatures reaching 35F or below.

Imagine driving along on a cold but bright winter's day, four people in the car warm and cozy. Now as you approach the higher mountain elevations the A/C compressor shuts down due to the declining temperature. At 65 MPH the windshield interior surface is becoming thoroughly chilled due to the impinging COLD airflow.

AND now that thin film of moisture is evaporating into the incoming airstream and being combined within the cabin atmosphere with the moist byproducts of human metabolism.

Very soon you will begin to small wisps of condensation at the lower corners of the windshield due to rising cabin humdity and a chilled windshield surface. Remember, now, the A/C is disabled
and cannot be used to dehumidify the incoming airstream. And even if it could be activated it's usefullness at dehumidifying an already cold incoming airstream is negligible at best.

But go ahead, activate the defrost/defog/demist function.

The result will very likely be exactly what I encountered in the winter of 92/93 in my brand new Lexus LS400.

A quite thoroughly and completely fogged over windshield.

When you activated the defrost/defog/demist function the result was that now ALL of the humid system airflow is routed toward the cold windshield surface.

What you REALLY need to do FIRST, is WARM that chilled windshield surface to raise it's dewpoint and begin to evaporate the already condensed moisture.

You can do that best by turning the heat demand of the system to MAX (the blower speed will usually increase automatically as you do this, if not...), and now once the heat is really flowing and the blower is at full speed then activate the defrost/defog/demist mode.

There is an aftermarket product available that about an hour after the vehicle is shut down will begin to run the system blower intermittently to disperse the moisture outside of the A/C plenum as it begins to evaporate from the evaporator vanes.

I understand that Ford is aware of your problem and will oftentimes recommend that the dealer install this device if the customer complains.


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Old 01-14-2005, 02:40 PM   #11
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Bump for a most excellent (old) post!
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Old 01-16-2005, 05:20 PM   #12
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Also, keeping the inside of your glass really clean will help defog them faster. The reason is the "film" that is on the glass holds moisture better than clean glass. Removing the film gives the moisture less "hold" on the glass, thus it defogs faster.

Window tint neither helps or hurts the situation.
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