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-   -   Auto A/C Recirc When Pollutants Sensed (http://www.bimmerfest.com/forums/showthread.php?t=726021)

RhoXS 10-04-2013 12:10 PM

Auto A/C Recirc When Pollutants Sensed
 
I would like to accurately understand the exact function of the A/C recirc button.

When the left light is lit the manual (2011, P104) states " ... a sensor detects pollutants in the outside air and controls the shut-off automatically.". I interpret this as meaning a sensor will force it into recirc mode when it detects some sort of pollution. Exactly what is it sensing with respect to "pollutants" and how does it do this?

I assume auto mode also just allows the logic to switch to recirc mode when the outside air temp is too high for efficient cabin cooling. But, this statement in the manual strongly implies that the system will only go into recirc when it senses "pollutants".

gfeiner 10-04-2013 12:58 PM

Auto A/C Recirc Whe Pollutants Sensed
 
I have wondered about the about the same thing. I think BMW embelished that description. They make it sound like they equip the AC system in their cars with Mass Spectrometers.


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RhoXS 10-04-2013 01:08 PM

Quote:

Originally Posted by gfeiner (Post 7877076)
They make it sound like they equip the AC system in their cars with Mass Spectrometers.

Wow! My thoughts exactly and that is obviously not the case.

Drewsky 10-04-2013 01:52 PM

The sensor is a hydrocarbon gas detector. You dont need a full-on mass spectrometer for this, they are built pretty cheaply and inexpesively. I just went searching through my computer for the document that talked about the sensor on my e46 (it had one too) but I can't find it. It works pretty well though, the recirc "flap?" inside the dash makes it evident when it changes and pretty much like clockwork when I stop at a light amidst cars, I can hear it close me to outside air.

Edit:

Some light googling found some tidbits too: If the AUC II sensor detects an increased level of pollutants in the environment from spark-ignition and diesel engines, the IHKA control unit will automatically switch to air recirculation mode.

02420X3 10-04-2013 02:34 PM

I noticed that the AUC II wasn't effective at detecting the dead skunk near a traffic light where I often stop on the way to the office. I'll work on dropping back a car or two...

Drewsky 10-04-2013 05:13 PM

Quote:

Originally Posted by 02420X3 (Post 7877337)
I noticed that the AUC II wasn't effective at detecting the dead skunk near a traffic light where I often stop on the way to the office. I'll work on dropping back a car or two...

Be behind an old car pre-catalytic converter at a stop light and that recirc baffle slams right shut! lol

RhoXS 10-05-2013 12:55 AM

Quote:

Originally Posted by RhoXS (Post 7876994)
I assume auto mode also just allows the logic to switch to recirc mode when the outside air temp is too high for efficient cabin cooling. But, this statement in the manual strongly implies that the system will only go into recirc when it senses "pollutants".

So, will the system also automatically go into recirc mode when needed for cooling?

Drewsky 10-05-2013 07:36 AM

Quote:

Originally Posted by RhoXS (Post 7878121)
So, will the system also automatically go into recirc mode when needed for cooling?

Not unless you push the max button

TerraLvr335i 10-05-2013 08:18 AM

Whatever it is, I find it works pretty well. On both my E90 and F25 it pretty much always prevented exhaust and similar smells into the cabin.

Liverman 10-05-2013 10:47 AM

Quote:

Originally Posted by Drewsky (Post 7878320)
Not unless you push the max button

Or push the Recirculate button twice to engage Manual Recirculation. Right LED near the "M" lights up.

Your temp setting and fan speed stay the same. With Max button, the fans goes on max and the temp goes to min as well as blocking outside air.


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