[snaketh]

Originally Posted by TajoMan

As a HVAC engineer, I had to test this out of my own curiosity. lol

In conclusion, center temp dial does not commend AC compressor.

However, AC compressor does come (or stay) on even with AC button turned off.

Right after initial engine start, AC compressor turned on even with AC button off.
It took about 5 minutes to AC compressor to turn off after engine start.

I verified it through Torque app engine load value.
When AC compressor engages, engine load goes up 2~3 % at idle.

Once AC compressor turned off, adjusting center vent temp dial did not turn on AC compressor (in both manual and auto mode).

However, if I lower the temperature on main temperature controls (driver and passenger), sometimes (not every time) it turns on AC compressor (with AC turned off with button).

I guess BMW took away some of the freedom to turn off AC compressor with AC button.
(Some manufacturers do that and I understand why they do it)

That explains why when I turned on the car the air was always AC.

You say you know why BMW took away some freedom with the AC, could you elaborate?

What is that center dial doing? Just diverting flow.

[TajoMan]

I don't know exactly why BMW setup HVAC this way.
In terms of taking controls away from user is to improve overall AC operation.

I can see the car turns on AC at the engine start if the ambient is higher than certain set point to quickly cool down the cabin.
It also helps to maintain AC compressor seal better. (circulate the oil to 'wet' the o rings)

In general, a lot of people does not know how to use AC properly (or how the AC works), so engineers who develop the system, sometimes, control the system regardless of the user input.
(i.e. forcing AC compressor on in defrost mode)

[krhodes1]

Originally Posted by snaketh

I did a similar test. Def AC air coming out that vent.

Question is: what should that knob be set to? In the middle?

It should be set to however you want. Personally, I usually set it in the middle with the main temp set to 70F summer and winter. If I feel warm, I turn the center dial down. If I feel chilly or the air on my hands is too cold, I turn it up.

I find it most useful in the winter, because I ALWAYS have cold feet. So I want nice warm air on my feet, but I want cooler to cold air to my face. Cars that can't accomplish this annoy me to no end, I have been spoiled by too many VWs, Saabs, and BMWs that can do this.