[Ron Jeffries]

Pic not M240i, but close enough ... Between the front and rear window defogger, under the temp knob? Doesn't seem to do anything or light up.

What is it?

And yes, when I'm next near my manual I'll look ...

[DaleHeinz]

I wonder if it's a little light sensor that is used to determine how much light is in the cabin to decide when to turn those lights from orange to white?

[TajoMan]

It's the temperature sensor for interior temperature.
It also measures sun load.

[Ron Jeffries]

yes, guide says interior temp sensor. what is sun load?

[BEM-S4]

Originally Posted by Ron Jeffries

yes, guide says interior temp sensor. what is sun load?

Son load is how much of one's income is devoted to supporting parasitic male offspring. According to my father it can be quite high.

[TajoMan]

Originally Posted by Ron Jeffries

yes, guide says interior temp sensor. what is sun load?

Sun load = Solar intensity (how much the Sun is shining)
It measures in W/m^2 (how much solar power per unit area)

Solar intensity measurement is used to adjust the interior temperature accordingly.

[Ron Jeffries]

huh. interesting. i’d think temperature would work ...

[p912guy]

You may have noticed it could be cool (50's) outside but the sun is bright and shining warming the car and if you feel air coming from the vents it's cool like the air conditioning is running as opposed to the heater. That's solar gain being compensated for. My BMW is the first car I've owned that does this. I'm not sure I'm a fan, but it is what it is.

[Ron Jeffries]

I wonder if that's why the temperature is never right.

[TajoMan]

BMW's auto HVAC control is just not very good.
(It's one of my complaint about my car, Auto HVAC and useless sun visor)

my previous 2011 Acura TL was almost perfect for Auto temp control.
In TL, I set at 72F all year long, never touched the setting and it was always maintaining perfect temperature.

Compare to that, BMW's Auto temp control really sucks. (at least in my 240 and wife's X3)
I need to adjust temperature setting fairly frequently between 70~73F to get the "feel" just right. It's not a good HVAC system.
Well, I'm super sensitive and picky about HVAC control because that's what I do. lol

[3.0L]

Originally Posted by Ron Jeffries

I wonder if that's why the temperature is never right.

Maybe you could try putting a piece of tape over the sensor and see what happens.

[Kolyan2k]

Sunload sensor is most likely inside mirror housing, not that

[kz1000]

[harma24]

Originally Posted by TajoMan

BMW's auto HVAC control is just not very good.
(It's one of my complaint about my car, Auto HVAC and useless sun visor)

my previous 2011 Acura TL was almost perfect for Auto temp control.
In TL, I set at 72F all year long, never touched the setting and it was always maintaining perfect temperature.

That's funny. I find the BMW auto mode quite good. Conversely, my 2014 Honda is awful; it cuts the fan to such a low rpm it barely circulates any air at all.

[TajoMan]

Originally Posted by Kolyan2k

Sunload sensor is most likely inside mirror housing, not that

Actually, you may be right.

I see there is different part # for the rear view mirror with Auto AC.

http://www.realoem.com/bmw/enUS/show...diagId=51_8588

[siwo]

Originally Posted by BEM-S4

Son load is how much of one's income is devoted to supporting parasitic male offspring. According to my father it can be quite high.

[moldcad]

Compared to the HVAC system I had in my first BMW (2002 E46 330i), my current 2015 M235i's works like a dream. AC on 365 days a year; "overall" temperature set between 19-21 C (simply depending on my current mood and physical state of being) - the only control I use often is the scroll wheel between the 2 central vents which so many people seem to not even know the purpose of...

The best HVAC system of all the cars I've had during my 46 years behind the wheel, and by far!

Piotr

[Ron Jeffries]

I have noticed that the scroll wheel makes it colder on blue and warmer on red but I confess I don't know exactly what it does or why. I supposed it was adjusting fresh air proportion? Now I have to go read the manual again ...

[Cumberlandjames]

I tell you, that center control is great driving with the top down on cool days. You can select it to warm and blow nice hot air at your hands from the dash vents. Also fantastic for AC when sitting in traffic. I think its great!

[TajoMan]

I think it's double edged sword.

Yes, it does add more level of control and fine tuning for interior temperature comfort in wider range of situations.
(it is great when you need a lot of defrost on windshield in heavy snow. put the main HVAC on full hot toward to windshield, then adjust the center vent temp to full cold so you don't get toasted.)

However, it defeats the purpose of Auto HVAC because it's additional manual adjustment.

(As a HVAC test engineer) my view of ideal auto HVAC control is, once you find a comfortable temperature setting, you should never need to touch it again in any ambient condition.
Again, it's just me being super picky about HVAC system.

[harma24]

Originally Posted by TajoMan

(As a HVAC test engineer) my view of ideal auto HVAC control is, once you find a comfortable temperature setting, you should never need to touch it again in any ambient condition.
Again, it's just me being super picky about HVAC system.

As a mechanical engineer myself, I aim to please 80% of the population. In any given room, one person will be too hot while another is too cold.

I look at the auto setting in my car the same way. It won't satisfy me 100% of the time, but as long as it satisfies me 80% of the time, its all good. I'll put the other 20% on me!

[Ron Jeffries]

I find the temperature rather variable, especially on the feet. My 135is didn't do that ... at least I think it didn't. But it didn't get to go out in the snow so I could be wrong.