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      09-11-2019, 08:01 AM   #1
-nexus-
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Exactly half of windscreen fogging up

Recently, my RHD 2010 135i N55 coupe has had the driver's side of the windscreen fog up almost during every drive. It's exactly the driver's half of the windscreen, the passenger side is unaffected. Using the windscreen de-fog button will clear the fog away but when I stop using it, it fogs back up again.

I have also noticed that occasionally the driver's face vents (vent to the right of the steering wheel, and the right-side centre vent) will emit a visible fog/mist when the fan is on a higher setting. The fog disappears almost immediately, is odourless, and the air conditioning temperature is fine and working as set. Again, this does not occur from the passenger side.

I always have the air conditioning set to auto on the lowest setting, anywhere between 20-24 degrees. The recirculate setting is also set to auto.

I am stumped as to what could be causing this. Internet searching suggests it could be a blocked A/C drain hose, but I read the transmission needs to be removed to get at it, so I'd like to avoid that if possible.

See below photo of the fogging issue.

Any suggestions or advice greatly appreciated!
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      09-13-2019, 01:29 AM   #2
-nexus-
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Bump!
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      09-13-2019, 09:07 AM   #3
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Ha! My dad lives in Wollongong.

Anyway, you don't need to remove the transmission to get at the drain. Well to do it properly you might, but you can feed a small wire or similar object up the drain pipe to unclog it. Aside from that, it does seem like one of your defogger vents is blocked or the vent tube came loose under the dash.

There's a lot of good information about cleaning the HVAC system here: https://www.1addicts.com/forums/showthread.php?t=739013
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      09-16-2019, 10:45 AM   #4
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Small world!
Thanks for the tips and the link to the thread, I'll give the wire trick a try just to be sure it's not blocked.

The defogger vents seem to be working, I can feel air coming from them and when I press the defogger button it does clear the windscreen (albeit a bit slowly). Combined with the occasional fog coming from the driver's face vents, I feel like there's an issue with the dual-zone A/C on the driver's side. Are there any specific components to the driver's side that could be the cause?
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      09-16-2019, 10:52 AM   #5
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If the AC drain vent is working and the weather is warm, you know the drain is working because of the puddle your car leaves when parked.

The difference between driver and passenger is flaps in the air distribution system, I don't think that is the issue.

My windscreen (windshield) fogs up due to some sort of chemicals or something. It does it when the heater is on too. I have to wipe it down. I've never had a car do this as much as my bimmer. Seems to be mostly on the drivers side. I don't know if it is plastics off-gassing or what.
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      09-16-2019, 12:19 PM   #6
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Quote:
Originally Posted by -nexus- View Post
...I feel like there's an issue with the dual-zone A/C on the driver's side...
FWIW I think this is the right track. Air is there, blowing, but more not dehumidified on one side. No idea unfortunately how it works.
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      09-16-2019, 08:53 PM   #7
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Quote:
Originally Posted by JimD View Post
If the AC drain vent is working and the weather is warm, you know the drain is working because of the puddle your car leaves when parked.

My windscreen (windshield) fogs up due to some sort of chemicals or something. It does it when the heater is on too. I have to wipe it down. I've never had a car do this as much as my bimmer. Seems to be mostly on the drivers side. I don't know if it is plastics off-gassing or what.
I've not noticed the puddle as much lately as temperatures have been cool and it's only early spring.

Your fogging issue is almost certainly vinyl fog, my car does it as well in the summer and I have to clean the windscreen a lot more frequently when outside temperatures are high.

Quote:
Originally Posted by tracer bullet View Post
FWIW I think this is the right track. Air is there, blowing, but more not dehumidified on one side. No idea unfortunately how it works.
I agree, unfortunately no idea how it works either. I doubt there are separate de-humidification circuits for each zone (correct me if I'm wrong!) so I'm leaning towards perhaps some moisture or pooling of water somewhere on the driver's side of the system.
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      09-17-2019, 10:08 AM   #8
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If you can find some technician training manuals you might learn a little about how the system works. There's a decent chance if one isn't available for the 1-Series, that a similar era 3-series works the same way. Might give some ideas of what to look into.

I was thinking you were blowing humid air (meaning it didn't get past an AC coil to remove the humidity, but if the A/C is working then... the blocked drain makes more sense if a small pool of water is being blown past and evaporated up onto the windshield.
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      10-31-2019, 11:06 PM   #9
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Brief update but no closer to a solution yet. There is visible water draining to the ground outside the car so the drain isn't blocked.
The visible fog from the drivers vents occurs usually during easy freeway driving, but the car windows will otherwise fog up gradually on any drive, even without visible fog coming from the vents.

The weather is warming up but not hot, and conditions are not out of the ordinary to any other time I've owned the car, so I don't think it's a weather or conditions issue.
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      12-29-2020, 01:58 AM   #10
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Quote:
Originally Posted by -nexus- View Post
Brief update but no closer to a solution yet. There is visible water draining to the ground outside the car so the drain isn't blocked.
The visible fog from the drivers vents occurs usually during easy freeway driving, but the car windows will otherwise fog up gradually on any drive, even without visible fog coming from the vents.

The weather is warming up but not hot, and conditions are not out of the ordinary to any other time I've owned the car, so I don't think it's a weather or conditions issue.
Hi Nexus. Did you find a exact solution? I have same problem on my e39.
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      01-01-2021, 09:35 AM   #11
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From my readings, this can be a symptom of a leaking evaporator. To test, you need to have the A/C system evacuated and a dye included in the re-charging of the system. Operate the system for a while, then visually inspect the evaporator. If it is leaking, dye will be visible (and it appears leaks typically occur where the evaporator tubes enter the tubesheet).
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      01-05-2021, 01:17 AM   #12
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Smile

Quote:
Originally Posted by MotoWPK View Post
From my readings, this can be a symptom of a leaking evaporator. To test, you need to have the A/C system evacuated and a dye included in the re-charging of the system. Operate the system for a while, then visually inspect the evaporator. If it is leaking, dye will be visible (and it appears leaks typically occur where the evaporator tubes enter the tubesheet).
Thanks for reply. Will be check it
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      01-12-2021, 06:27 AM   #13
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Agree about evaporator sounds like a leak in it. Might be off base but what if you got one of those freon charging kits and see if it takes any freon. Don't remember if there is any stop leak in it, if so I wouldn't use it.
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      11-28-2023, 07:11 AM   #14
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I don't mean to resurrect this, but for closure and for anyone else looking this thread up, the culprit in the end was a leaking heater core. I don't know why it only resulted in half the windscreen fogging up, but after the core was replaced the issue disappeared.
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      11-28-2023, 01:03 PM   #15
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Quote:
Originally Posted by -nexus- View Post
I don't mean to resurrect this, but for closure and for anyone else looking this thread up, the culprit in the end was a leaking heater core. I don't know why it only resulted in half the windscreen fogging up, but after the core was replaced the issue disappeared.
Thanks for sharing this. 🤙
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