No HVAC Fan, but Defrost Works

[kiloTHREE]

Whoa, ran into a weird one coming home from the airport last week.
The temp control was set to auto 74F. The fan never rampped up like it does once the engine is warm.
In fact, even manually setting vent/feet and the fan selector did nothing.

However, I could use the front defrost button on the far right side and that would kick on the fan full bore and get me some heat on the way home.

My car regularly sits at the airport on weekdays so -20 to 0 F degree temps are nothing new.

Took it home, checked a bunch of fuses, ran for codes, nothing out of the ordinary.

Fired it up the next morning and everything is business as usual.:

[HBWT]

Lucky you, good that it was a self-repair issue

[Portly]

Your battery was low. I've had the same issue during cold weather / short trip situations. Once the battery gets charged back up again, the ECU will re-enable higher fan speeds. (Don't ask me why the alternator doesn't just charge at a higher rate...)

[kiloTHREE]

Originally Posted by Portly

Your battery was low. I've had the same issue during cold weather / short trip situations. Once the battery gets charged back up again, the ECU will re-enable higher fan speeds. (Don't ask me why the alternator doesn't just charge at a higher rate...)

That would make sense, odd as it is. That was one of the longest and coldest lengths I've ever let my car sit.

[Mirko]

Had this happen to me too. Sadly when I was running just the defrost setting the windshield cracked. Took a few drives to reset the hvac controls but all back to normal. Pretty dumb that the system does that sort of limp mode. I've never experienced that in any of the other bmw's ive owned.