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      10-29-2009, 08:25 PM   #1
pplace
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HVAC functions: cold air, recirculation, fog control

So, I am thinking that I know (sad to say) more about the user operation of the HVAC system than the SA. Either that or what I think I know... I don't!

Recirculation system has 3 settings:
1. lights off = no recirc
2. left light on = intermittent
3. right light on = air recircs all the time

Rotary dial at the top of the console:
1. All red bars = hot air (if heat is on) coming out of the dash vents.
2. All blue bars = cold air (even if heat is on) coming out of the dash vents.

Therefore, it is possible to have cold air blowing out of the dash vents even when the system is set to AUTO and 40 degrees hotter than the ambient air temp. Someone said that this is to keep air in the driver's face in order to keep him awake. Someone else said this is to keep fog from forming in the windows and causing crashes.

SA said....what? That means both the heater is running AND there is cold air being blown out at the same time and that doesn't make any sense.

Why does it do this otherwise?

Has anyone figured out why the HVAC does what it does? Thanks.
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      11-07-2009, 06:56 PM   #2
pplace
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Will fog up windows reliably

When it is cold but not freezing outside and even when it is not raining, the X3 will reliably fog the inside of the windows.

- Heater on hot enough, say 25 degrees above ambient temp
- Snowflake button off
- Recirc on
- Fog in a few seconds

Mine does this pretty consistently so far and it does so without any of the other usual suspects for window fog.

So the AC stays on and the recirc button is always off during the cold season.
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      11-08-2009, 08:41 AM   #3
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      11-08-2009, 03:45 PM   #4
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Quote:
Originally Posted by rs6655 View Post
I've seen these before but I watched it again since you pointed it out. I noticed:

1. He said to keep the recirc on the A mode all the time. Given the problem with the window fog, I do not know why he doesn't say to keep it off when the heater is on. Why take chances? Given the cold and wet German climate, I don't know why they don't take this opportunity to mention condensation and safety. They must have more than their fair share of it both inside the windows and on the outside on colder days.

2. I thought the hot/cold dial above the center vents controlled all the forward dash vents including the two to the sides and not just the center ones that he mentioned. I can have a bit of warm air coming out of the small square vents at the side/top of the dash and cool air coming out of the vents below them.
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      11-21-2009, 09:49 AM   #5
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Quote:
Originally Posted by pplace View Post
I've seen these before but I watched it again since you pointed it out. I noticed:

1. He said to keep the recirc on the A mode all the time. Given the problem with the window fog, I do not know why he doesn't say to keep it off when the heater is on. Why take chances? Given the cold and wet German climate, I don't know why they don't take this opportunity to mention condensation and safety. They must have more than their fair share of it both inside the windows and on the outside on colder days.
My wife and I are retired and do a lot of traveling (30K in one year). We've driven our 2009 in every type of weather and have never had a fogging problem. I have had to add hot air to the winshield when it's really hot and humid outside to keep condensation from building up on the outside of the windshield. But that's just because we like to keep the car cool and the climate control is so good at keeping it that way.

I've owned more cars than I can count over the years and my X3 is hands down the best. That includes two other BMW's.... an E12 and an E90.
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