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Old 5th August 2008, 17:34   #91
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For the benifit of understanding, let me post what I had mentioned earlier. Condensation of vapours as fogs happens on an object or its surface when there are enough moisture in the air and at the same time the object's temperature is considerably low (or lower than the surrounding) to cause a saturation. This is true, not only for car glasses, but also for anything, such as a milk packet just taken out from a refrigerator or an ice cream parcel container that you are carrying on a day air moisture is high.

Keeping that in mind, how to clear the fogs on the windows and windshield? Fogs will be formed inside the glasses if glass is cooler than the cabin air. Fogs will be formed outside the glasses if the glass is cooler than the outside air (assuming the air to have enough moisture).

As you can see, when the glass is cooler than the inside or outside, we have problem either inside or outside. The best solution is to keep the temperature of the glass at least same as or higher than the inside air and outside air. For those who do not have heater, we cannot make the glass warmer than air on both the sides. And we cannot control the air temperature outside. So, the only control we have is the inside cabin air temperature. Maintain the cabin air temperature always cooler, if not same, as compared to the outside.

And whatever people tell their problem, being wiper, blah blah, I'm not going to believe it, because I know that those glasses do NOT have MAGIC to form some fog out of nothing. Even a bad wiper blade is good enough if it wipes the water off on the outside. A thin unwiped water is better visible than grey white fog. In the inside, a good temperature control is good enough to avoid fog.

One more thing, using cool air is more effective than the hot air blow unless the glasses have inbuilt heater. During the cool air blow, we should keep re-circulation mode. Too much cold air blow to the glass for prolonged time on rainy day can make the glass even more colder than the inside cabin, leading to fog again inside. If this is the case, stop blowing to the glass. You can continue cold air a/c to the face and leg (for the cabin air in general).
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Old 5th August 2008, 17:40   #92
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Most of us use a razor for shaving.
After a couple of shaves the blade although its still quite sharp just won't shave right.

Wiper blades do much the same thing. They remove the water and the grime from the windscreen. If they have gone old they can remove the water but leave a little grime on the screen. This is why replacing the blades helps. IMHO.
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Old 5th August 2008, 18:29   #93
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But at the same time, no lady use a razor blade to shave, right? Why should the fog come in the first place? If it is for the purpose of wiping water, I can undestand. If it is a problem of fog or moist, it is not a wiper problem and people don't seem to get this point. Anyway, I have given my thoughts more than once on this.
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Old 5th August 2008, 20:36   #94
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Quote:
Originally Posted by opendro View Post
Condensation of vapours as fogs happens on an object or its surface when there are enough moisture in the air and at the same time the object's temperature is considerably low (or lower than the surrounding) to cause a saturation. ........
The best solution is to keep the temperature of the glass at least same as or higher than the inside air and outside air.
I beg to disagree.
The first part of your post quoted above contains the germ of the answer - The fogging occurs due to condensation of water vapour.
One solution is to have the a/c on, more than cooling, it de-humidifies the inside of the car, i.e, renders the air inside drier, ergo, you have no vapour to condense.
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Old 6th August 2008, 02:02   #95
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Yesterday when it was raining, I realised that the windscreen was extremely misty/foggy.
Unfortunately, our domestic help has been using some dirty cloth which probably had oil/grease on it (my regular cleaning guy is on leave) and I realised the windscreen + all other glasses were rather coated completely with something very greasy.

The wipers started skidding bad and visibility reduced even though I tried to use the wiper water which has Colin mixed in it. I tried to clean it off with a clean cloth and tissues but the coating needs some serious scrubbing.

How can I clean the car's glass to remove all the oiliness on it? I have no special glass products so please advise a good home remedy!
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Old 6th August 2008, 10:13   #96
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Quote:
Originally Posted by filcord View Post
I beg to disagree.
The first part of your post quoted above contains the germ of the answer - The fogging occurs due to condensation of water vapour.
One solution is to have the a/c on, more than cooling, it de-humidifies the inside of the car, i.e, renders the air inside drier, ergo, you have no vapour to condense.
Your knowledge is completely misplaced. You cannot de-humidify inside or outside the car by any means. People are continuously breathing out warm moist and you are supposed to re-circulate the inside air. Warm air can hold more humid, but we cannot make the glass warm because of the cold shower or dew outside, unless we have heater.

This is the last attempt from me to make people understand. The goal of whatever you try to do is NOT to allow saturation to happen on the glass, by warming the glass or by making the air near the glass (or inside the car) cooler than the glass. That is why I mentioned that if you are blowing cold air to the glass, don't blow very chilled air for too long. That can make the glass even cooler, causing fog, not only inside but outside also. You can probably blow very chilled air initially and then reduce the chillness after sometime or blow towards face/leg.

I'm comparatively new to cars and learning. But what I said is the truth about the fog/mist. Take it or leave it. Sorry I had to take this attitude towards people, who are too full to take anything.
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Old 6th August 2008, 10:17   #97
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Quote:
Originally Posted by ankitahuja View Post
How can I clean the car's glass to remove all the oiliness on it? I have no special glass products so please advise a good home remedy!
I don't remember any brand. But most car accessories shop will have something or other agent to clean the glass. I don't remember, but I got one and didn't have to use yet. So, not sure if that helps or not even. It may be worth a try.
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Old 6th August 2008, 11:25   #98
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opendro:
There are two different issues that hamper visibility.

#1:
formation of Fog/ Mist on the windshield. IMHO: You are absolutely correct.

#2:
The action of wipers leaving a thin glaze on the windscreen that disappears in a few moments. This is the problem caused by old/ worn out/ bad wipers. Replacing wipers solves this probelm as they are able to clean the glass much better and remove the layer of grime that has formed on it.
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Old 6th August 2008, 11:41   #99
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Quote:
Originally Posted by bblost View Post
opendro:
#2:
The action of wipers leaving a thin glaze on the windscreen that disappears in a few moments. This is the problem caused by old/ worn out/ bad wipers. Replacing wipers solves this probelm as they are able to clean the glass much better and remove the layer of grime that has formed on it.
Yeah. You are right. I absolutely agree that issue #2 is a separate problem. It is like our looking mirror. Wash with water and wipe immediately. If there are some dirt sticking on surface and surface is not yet fully dried because I washed just now, there will be a thin layer of foggy feeling, which gives hazy reflection picture. Thanks for the clarification.
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Old 7th August 2008, 00:07   #100
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Quote:
Originally Posted by opendro
Your knowledge is completely misplaced. You cannot de-humidify inside or outside the car by any means.
opendro, I agree with whatever you had to say, except this one. AC DOES de-humidify air. Well known water drain out of AC system is nothing but the water removed from air! Your earlier posts had some contradictions, but still hold true just because of this fact (see below).

Quote:
Originally Posted by filcord View Post
I beg to disagree.
The first part of your post quoted above contains the germ of the answer - The fogging occurs due to condensation of water vapour.
One solution is to have the a/c on, more than cooling, it de-humidifies the inside of the car, i.e, renders the air inside drier, ergo, you have no vapour to condense.
IMHO, both of you are right, but I am not so sure if he appreciates the fact that AC not only removes heat but also water content from air.

Quote:
Originally Posted by opendro View Post
The best solution is to keep the temperature of the glass at least same as or higher than the inside air and outside air. ....... Maintain the cabin air temperature always cooler, if not same, as compared to the outside.
Your 1st statement is true, but it contradicts with the last statement in above quotes. Still, I think the later works actually because of de-humidification by using AC.

Quote:
And whatever people tell their problem, being wiper, blah blah, I'm not going to believe it, ..... a good temperature control is good enough to avoid fog.
I agree, the problem at hand is not "fogging" here, it's the layer left behind by wipers. Good that most of us agree on that, I had mentioned it in earlier post #70 (Foggy/Misty windshield-urgent help required)

Quote:
One more thing, using cool air is more effective than the hot air blow unless the glasses have inbuilt heater.
The first part of this statement is true again due to de-humidification. I don't agree on the later part after "unless". In built glass heater (defrosters) will always make it relatively better, regardless of what you are doing using AC and heater.

Quote:
Too much cold air blow to the glass for prolonged time on rainy day can make the glass even more colder than the inside cabin, leading to fog again inside.
I think in this case, the condensation happens from outside, not inside. Once again, due to de-humidification effect, cold air blowing from AC will not fog it no matter how cold it is, it's the outside air which condenses because of lower temperature.

This thread is going full circles now
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Old 7th August 2008, 10:05   #101
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Santosh, we both now agreed that a cold glass is the culprit for the condensation of the water vapour on its surface.

Now, we will come to some other facts that we didn't agree, i.e. humity. As I mentioned, our warm breath is one main culprit for the humidity. And A/c does not remove this, specially in re-circulation mode. Let me be very clear on this. Imagine yourself breathing in a closed glass jar on a warm day or cold day. Or imagine a glass of normal temperature water in a "sealed" glass jar. No fog as long as both water and glass jar remain at that temperature. Now, cool down the glass jar by taking into a colder place, say, refrigerator, in the same "sealed" state. You will see fog inside. You will see the same if you pour warm water and seal the jar. I don't know if humidity has changed in this scenario. But as far as human breathing is concern, I can tell you certainly that we breathe out the same amount of humid as long as the internal body temperature is same. And that just does not saturate on a warm day as hot air can hold more humid. When glass is cold, the vapour goes there a saturates there. If we make the air cooler, it will try to condense in the cooler air. Assuming there are enough amount of humid in the air and temperature is cold enough to condense that much humid, that is what is rain. Yeah, once, it becomes water in liquid form, the humidity comes down.

I hope this clarifies.
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Old 7th August 2008, 12:54   #102
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What about water getting drained from cooling coil? Where does it come from?

I believe even in recirculation mode, a car cabin is not strictly an air tight container. If it was, then there would be no opening for condensed water from AC to flow out.
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Old 7th August 2008, 14:32   #103
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Quote:
Originally Posted by santosh.s View Post
What about water getting drained from cooling coil? Where does it come from?

I believe even in recirculation mode, a car cabin is not strictly an air tight container. If it was, then there would be no opening for condensed water from AC to flow out.
Off topic. A/c basically cools down a part of the condensor coil. You blow air from that. Or in heater, you heat one filament, and blow air from that. That air to be blown need not be from outside.

Now, where does the water coming from? Some parts in the outside will be cooler than the outside air. This will cause outside water vapour condensation. If you do a long drive with full A/c on a very sunny day, you might be able to see water droplets outside the window or rear glass. That water is nowhere related to the A/c unit under your bonnet.
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Old 7th August 2008, 16:17   #104
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opendro, again agreed to whatever you explained. But more than that, here is the explanation regarding water draining out of AC, as per my understanding- as air is blown through cooling coil, a lot more condensation happens there as compared to other places that you mentioned. This water can even freeze and create ice (like freezer inside home refrigerators), but it is avoided by an electronic control of compressor. There is a DEDICATED pipe to carry this water out.
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Old 9th September 2008, 22:28   #105
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Hi All, I just discovered this thread and was taken aback about other experiencing similar issues.
Recently had been to Udupi in my Swift VDI and started raining. I switched on the AC to windshield mode with non-recirculating air (fresh air). the temperature was set to minimum. Though it was a slight drizzle, the windscreen started fogging from the outside. I try to maintain the outside and the inside temperature almost equal. The conditions outside was pretty humid with slight drizzle. The fogging started from the lower center of the windscreen and slowly started to move up till the halfway mark (almost triangle shaped). "It was not the typical fogging effect, but more like crystalline frost marks following the wipe pattern (here's the difference: You can't write on it with your finger unlike the regular fog on glass. It remains like a stain)." I had recently got the blades for the wipers replaced. Driving in the night on the NH was a nightmare at that point of time with the opposite traffic with blasting high beams. I though the fogging was due to dust/oil sticking to the windscreen. I stopped and washed the wiper blade and windscreen with face wash which was in the car. Started driving and fogging started. This happened even after I had the driver side glass lowered a little.... Finnaly reached the destination, but had to be really careful and the experience was quite scary... A similar incident occured almost a year back when I was passing through Jog Falls Ghat section (caused a minor accident (dent on driver side door) with a tempo trax from the opposite direction) and it was a similar kind of rain..

Please help....Any thoughts on this??
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