Quote:
Originally Posted by evan_calgary
Anyone know the conditions required for the car to disable the HVAC fans? Is this a given battery draw or a % of battery life remaining? I should have been at 100% battery or darn close but it was also mighty cold outside.
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First, a side note: My car is an N20 engine, and acts the same, so the issue is not specific to the engine.
I believe (but do not know for certain) that the system does this once the battery drops below a certain capacity, which my experience implies is somewhere in the 45% - 50% range. I've monitored this using the Bimmerlink app, which is a handle tool to have.
Now, if you're thinking, "That can't be it - my battery is brand new!" - lead-acid batteries lose a lot of capacity at colder temps. My research is far from exhaustive, but some charts indicate that an AGM lead acid battery has less than 25% of its rated capacity when the temps are down at -40 (F or C - they're the same temperature at -40). So even a brand new battery might trigger this issue when the temps get so cold.
I can't begin to speculate why BMW thinks this sort of response is acceptable, when most cars just ignore the situation and assume the alternator will put out more than enough power to handle all the electrical loads - but for whatever reason, they do. I find it very annoying, but after dealing with it every time it gets fairly cold, I've come to the conclusion that this is just how it is with these cars, and there really isn't anything to be done about it.
_Jeff