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  #1  
Old 07-21-2003, 08:10 PM
e46_325xi e46_325xi is offline
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Unresolved Safety Issue

Ok guys,

Here is what I think is a major safety issue that I experience at times and I am sure some of you have experienced it as well:

I am driving down the road with my A/C on, when I think it would be nice to turn off the A/C and get some fresh air. Upon acting on this, within a minute or less, my entire windshield rapidly fogs up and reduces my visibility to virtually zero. The only way for me to avoid an accident is to immediately stop driving, if possible, or frantically begin wiping the windshield with whatever I have available (while trying to use the other hand to steer the car and keep my eyes on the road). This sounds like a serious safety issue to me. I have not brought this to the attention of my service department, but from the few reports I have heard, I feel they will say it is "normal".

Has anyone had any luck in resolving this?

PS. No, I do not have either one of the recirculate options turned on. The one other way to clear the fog is to open all windows and keep driving for a while. Given the visibility, I am sure that will result in an accident.
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  #2  
Old 07-21-2003, 08:15 PM
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Nick325xiT 5spd Nick325xiT 5spd is offline
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Clearly, it's too humid outside when you do this.

If you want fresh air, open the windows.
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  #3  
Old 07-21-2003, 08:28 PM
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3seriesbimmer 3seriesbimmer is offline
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happened to me today...luckily my girlfriend was in the car and powered down all the windows...I couldn't see a thing....it happens when the outside temp is too humid.....AC SUCKS the moisture out of the air thus causing the window to fog up quickly.
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  #4  
Old 07-21-2003, 10:54 PM
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*reposting this from a General thread* The trick I learned:

-Clean and dry the window.
-Put a little cheap liquid soap on a clean, dry cloth.
-Apply to the inside of the window; cover every bit.
-Buff out with a clean, dry cloth.

Works great to get rid of fog.
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  #5  
Old 07-21-2003, 11:03 PM
marcelgood marcelgood is offline
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Physics 101 my friend. Like 3seriesbimmer mentioned, the AC does not only cool the air, but it also de-humidifies it. So, if you cool down your interior, the windshield is cooler inside than outside. Now when you suddenly turn off the AC, humid air comes in through the vents and immediately condenses on the windshield. This is why on rainy days the AC helps you keep the windows from fogging up. If you live in dry climate you won't have this problem.
  #6  
Old 07-21-2003, 11:04 PM
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Doesn't any car do this?

I don't think the weather around here (despite the recent 90deg/60%+) would allow me to even try this. though.
  #7  
Old 07-21-2003, 11:09 PM
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Quote:
Originally Posted by Kaz
Doesn't any car do this?
Dunno, my other car doesn't have A/C.

But it did fog on cool days (hot air in the cabin, cold windshield) until I did the soap thing.
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  #8  
Old 07-21-2003, 11:22 PM
marcelgood marcelgood is offline
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Quote:
Originally Posted by The Roadstergal

But it did fog on cool days (hot air in the cabin, cold windshield) until I did the soap thing.
Leaving the AC on even on cool days should do the trick as well and yes other cars do the same thing. The incoming air will be slighlty cooled and rid of the moist and then reheated. BTW, this is how building ACs work. Did you know that those ACs always cool the air even in the winter and then heat it up to the desired temperature? Some will even humidify the air after it has been heated to keep the humidity at a desired level regardless of how humid it is outside. Car ACs don't do that, though.
  #9  
Old 07-22-2003, 04:53 AM
andy_thomas andy_thomas is offline
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Quote:
Originally Posted by e46_325xi
Ok guys,

Here is what I think is a major safety issue that I experience at times and I am sure some of you have experienced it as well:

I am driving down the road with my A/C on, when I think it would be nice to turn off the A/C and get some fresh air. Upon acting on this, within a minute or less, my entire windshield rapidly fogs up and reduces my visibility to virtually zero. The only way for me to avoid an accident is to immediately stop driving, if possible, or frantically begin wiping the windshield with whatever I have available (while trying to use the other hand to steer the car and keep my eyes on the road). This sounds like a serious safety issue to me. I have not brought this to the attention of my service department, but from the few reports I have heard, I feel they will say it is "normal".

Has anyone had any luck in resolving this?

PS. No, I do not have either one of the recirculate options turned on. The one other way to clear the fog is to open all windows and keep driving for a while. Given the visibility, I am sure that will result in an accident.
If I squint I can *sort of* see what you mean by "safety issue", but this is still a bit like saying "if I operate the car's controls in a particular manner, in particular by depressing the accelerator hard and turning the wheel to the right, I can run over pedestrians. Will BMW issue a recall for this?"

I have driven plenty of cars whose windows misted up quickly because - through unfamiliarity or lack of concentration - I chose settings which maximised the chances of fogged-up windows. I merely tweaked the controls in a manner which reduced the fogginess, and resolved not to select settings which resulted in foggy windows in the future.
  #10  
Old 07-22-2003, 05:33 AM
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Quote:
Originally Posted by Kaz
Doesn't any car do this?

I don't think the weather around here (despite the recent 90deg/60%+) would allow me to even try this. though.
I've never turned off the a/c in teh summer in the wagon, but it's happened in every other car (with a/c) I've ever driven.

There is another fogging problem that happens with many cars in humid conditions at night. With the a/c set to the coldest temps possible the windshiled will cool to the point that water vapor in the outside air will condense on the outside of the windsheild. It's just like a glass of ice water sweating. Of course, you can use your wipers to clear it, but it's still a PITA. It doesn't happen during the day because the sun is heating the windsheild beyond the a/c's ability to cool it. Adjusting the climate controls to make it a little warmer in the car will usually stop the condensation from happening
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  #11  
Old 07-22-2003, 08:30 AM
kdshapiro kdshapiro is offline
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This is not a BMW problem, it's a physics problem.
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  #12  
Old 07-22-2003, 08:40 AM
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It may seem to be more of a "problem" on the Bimmer because the blower/vents cover the windshield with air better than some other cars... what makes the defroster work more effectively also makes the condensation issue more noticable.

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  #13  
Old 07-22-2003, 10:15 AM
sshuit sshuit is offline
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This is the problem with kids today... first little sign of a challenge and they play the "canna change the laws of physics" card.

Harumph , back in my day we'd change the gravitational constant of the universe before lunch and do away with heisenburg before dinner.



Quote:
Originally Posted by kdshapiro
This is not a BMW problem, it's a physics problem.
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  #14  
Old 07-22-2003, 10:24 AM
marcelgood marcelgood is offline
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Quote:
Originally Posted by sshuit
This is the problem with kids today... first little sign of a challenge and they play the "canna change the laws of physics" card.

Harumph , back in my day we'd change the gravitational constant of the universe before lunch and do away with heisenburg before dinner.

. I didn't wanna call him a dumb nut, but this is a nice way of putting it.
  #15  
Old 07-22-2003, 01:23 PM
e46_325xi e46_325xi is offline
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Guys,

I do not think this is an inevitable physics issue. Nor do I think it amounts to hazardous operation (i.e. tantamount to turning your steering wheels at high speeds). I also think it is a problem somewhat peculiar to BMWs.

In my experience with several previous vehicles and rentals, I have not found this problem to be as extreme as it is in my car. My best guess (and yes, I admit this is just a guess) is that the BMW circulation system does a poor job of drawing in fresh air and also does a poor job of dissipating the moisture that the A/C draws out of the air. In other words, the moisture coming out of the dehumidifying process somehow remains trapped in the system and rapidly enters the interior when the A/C "snowflake" button is deactivated.

Why do I think this? Let me give you another scenario (which would essentially rule out marcelgood's cooler interior vs. warmer exterior hypothesis):

On Day 0, I drive the car with the A/C on throughout, return home and park the car. On Day 1, I drive out, find it is really nice out, and would like to turn on the fan without the A/C. Immediately, the windshield alarmingly fogs up and reduces visibility. (This only happens when the car has previously been driven with the A/C on...which leads me to believe that it is happening because the moisture trapped in the A/C from the previous dehumidifying process was not dissipated by running the fan without the A/C for an extended period.)

Yes, everytime I decide to drive without the snowflake activated (after previously driving with the A/C), I could decide to run it for an extended period while the car is stationary. Yes, I could always decide to drive with the windows down. But sometimes, these elaborate workarounds are just not convenient. And it appears a little much to do when one does not have to do these things in other vehicles.

Anyway, thanks to all for your responses. I am beginning to think that perhaps this problem is more extreme in my particular car than in other bimmers. Perhaps I should bring it to the attention of my service department.
  #16  
Old 07-22-2003, 01:27 PM
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Quote:
Originally Posted by e46_325xi
Guys,

I do not think this is an inevitable physics issue. Nor do I think it amounts to hazardous operation (i.e. tantamount to turning your steering wheels at high speeds). I also think it is a problem somewhat peculiar to BMWs.

In my experience with several previous vehicles and rentals, I have not found this problem to be as extreme as it is in my car. My best guess (and yes, I admit this is just a guess) is that the BMW circulation system does a poor job of drawing in fresh air and also does a poor job of dissipating the moisture that the A/C draws out of the air. In other words, the moisture coming out of the dehumidifying process somehow remains trapped in the system and rapidly enters the interior when the A/C "snowflake" button is deactivated.

Why do I think this? Let me give you another scenario (which would essentially rule out marcelgood's cooler interior vs. warmer exterior hypothesis):

On Day 0, I drive the car with the A/C on throughout, return home and park the car. On Day 1, I drive out, find it is really nice out, and would like to turn on the fan without the A/C. Immediately, the windshield alarmingly fogs up and reduces visibility. (This only happens when the car has previously been driven with the A/C on...which leads me to believe that it is happening because the moisture trapped in the A/C from the previous dehumidifying process was not dissipated by running the fan without the A/C for an extended period.)

Yes, everytime I decide to drive without the snowflake activated (after previously driving with the A/C), I could decide to run it for an extended period while the car is stationary. Yes, I could always decide to drive with the windows down. But sometimes, these elaborate workarounds are just not convenient. And it appears a little much to do when one does not have to do these things in other vehicles.

Anyway, thanks to all for your responses. I am beginning to think that perhaps this problem is more extreme in my particular car than in other bimmers. Perhaps I should bring it to the attention of my service department.
In terms of dealing with the issue, you oculd leave the compressor on and adjust the temp and fan speed to your comfort level.
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  #17  
Old 07-22-2003, 02:03 PM
marcelgood marcelgood is offline
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Quote:
Originally Posted by e46_325xi
Why do I think this? Let me give you another scenario (which would essentially rule out marcelgood's cooler interior vs. warmer exterior hypothesis):

On Day 0, I drive the car with the A/C on throughout, return home and park the car. On Day 1, I drive out, find it is really nice out, and would like to turn on the fan without the A/C. Immediately, the windshield alarmingly fogs up and reduces visibility. (This only happens when the car has previously been driven with the A/C on...which leads me to believe that it is happening because the moisture trapped in the A/C from the previous dehumidifying process was not dissipated by running the fan without the A/C for an extended period.)
I must say that I have never observed such a behavior. If I want to, I can turn of the A/C on the next day if I have driven it with the A/C on the previous day, but my windows don't fog up. Having said that though, I never turn off the A/C. It has been stated in other threads, that BMW uses a variable compressor, so if it doesn't have to cool the air, the compressor basically idles. I don't even turn it off if I open the windows, because I only open the windows if it's cool enough outside, hence the compressor doesn't have to cool the air anyway.
  #18  
Old 07-22-2003, 02:07 PM
Alex Baumann Alex Baumann is offline
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Quote:
Originally Posted by e46_325xi
On Day 1, I drive out, find it is really nice out, and would like to turn on the fan without the A/C. Immediately, the windshield alarmingly fogs up and reduces visibility. (This only happens when the car has previously been driven with the A/C on...which leads me to believe that it is happening because the moisture trapped in the A/C from the previous dehumidifying process was not dissipated by running the fan without the A/C for an extended period.)
.
The reason for this is the air coming out from the blower/vent is warmer than the windshield at that moment. (like when you breath on a mirror or glasses)

Here's a trick which I use in such cases : Lower the temperature a few degrees and push the full blow button for the front window. In a very short time of period, you'll see the fog disappearing, starting from the bottom of the windshield.
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  #19  
Old 07-22-2003, 02:24 PM
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Another thing just crossed my mind. When the vent controls are set to Auto (Auto button light is on but the AUTO is not in the display), air is routed to the 3 sets (foot/face/glass) of vents as the system sees fit. So if the temp/humidity conditions are right, and the car is started with the vents set to the glass by the Auto system, all the warm, moist air will hit the glass.

Try driving around with the vents set manually to 'face' only and see if the problem goes away.
  #20  
Old 07-22-2003, 02:50 PM
marcelgood marcelgood is offline
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Quote:
Originally Posted by Alex Baumann
The reason for this is the air coming out from the blower/vent is warmer than the windshield at that moment. (like when you breath on a mirror or glasses)

Here's a trick which I use in such cases : Lower the temperature a few degrees and push the full blow button for the front window. In a very short time of period, you'll see the fog disappearing, starting from the bottom of the windshield.
Actually, it's still the moisture that's causing it and not the temperature of the air. Human breath is very humid and warm and this combination is causing the mirror to fog up. Try blowing warm air from a hairdryer at a mirror and you will notice that the mirror doesn't fog up. I kinda have to agree with e46_325xi, that in his particular case it sounds like his system traps moisture that comes out the next time he starts the car with the A/C off.

e46_325xi, when was the last time your dealer replaced the micro-filter? I just thought of this, but it could be that your filter is soaked. Just an thought, though.
 

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