F30 defrost windscreen button

[RUSSELLM]

The climate control has a button on the bottom left, for defrosting the windscreen. Basically chucks hot air at all of the top vents.

I notice in my car, that it doesn’t activate at full fan speed. It’s 1 speed below maximum. Not really a problem, as I can turn it up each time. But can someone confirm their car does the same please ?

I could swear my old E90 went on max attack when I used to press that button.

Edit... Found a video here... https://youtu.be/-snHTpWpNKQ

at 1.40, the demo car does exactly the same as mine. So I guess it’s normal.

Edited by RUSSELLM on Wednesday 30th October 23:25

[Pica-Pica]

OP, I will check later, against full manual fan speed, but it seems fast enough to me. I do know that when I press it, it builds up to full speed over a second or two, but not immediately at full speed. Out of interest, is yours a pre or post LCI F30?

ETA. Just checked. Yes, the screen clear on mine goes to step 6 of 7 (it seems fast enough, but I can manually press it up to step 7 of 7). Interestingly, when the screen clear button is off, the auto mode only has 5 steps, which you can manually over-ride. Maybe it is not to shock the screen with over-heat? Maybe it is to keep the cabin noise lower when starting off, so as to hear traffic? Who knows. Not noticed it before, and not an issue. Mine is 66 plate too.

Edited by Pica-Pica on Thursday 31st October 09:57

[RUSSELLM]

Thanks, It’s a post/66 plate.

On mine , it just seems a bit random that when I press defrost, it starts at fan speed 6 of 7

I could swear my E90 went at full tilt, which seemed to make more sense.

[Pica-Pica]

Thinking about it, that does seem more and more like a test outcome solution. Something was discovered on a development test (thermal shock in extreme weather?) and then the setting was pulled back to a lower automatic max speed.

[Triumph Man]

I discovered similar on my Girlfriend's Mini Countryman - when "max A/C" is pressed, the fan speed will not go all the way up - there is still one "bar" left. I've always wondered why...

[Speed addicted]

My F36 does it too, I was also wondering about it. Suppose it must be normal!
Previous BMWs went onto full speed I'm sure.

[RUSSELLM]

Lad at work with a newish Mercedes, said his starts up at speed 5 of 7.

Range Rover’s start up at 7 of 7.

Got me intrigued now as to what the reasoning is

I wonder if the manufacturers have an electric boost on cold start, and have determined that air speed crossing over it, as an optimum flow rate to maintain heat ?

[Speed addicted]

RUSSELLM said:

Lad at work with a newish Mercedes, said his starts up at speed 5 of 7.

Range Rover’s start up at 7 of 7.

Got me intrigued now as to what the reasoning is

I wonder if the manufacturers have an electric boost on cold start, and have determined that air speed crossing over it, as an optimum flow rate to maintain heat ?

I hope it’s that, but suspect it was because the fan was too noisy.

[4rephill]

I'm struggling to believe the thermal shock theory.

The front screen defrost isn't an instant, hot temperature onto the glass, the temperature increases gradually as the car warms up.

I suspect it's more a case of slowing the air flow down slightly, to help keep the warm air on the screen defrosting, rather than having it bounce off the glass and be less effective.