We've had the car for just shy of a month, 166,xxx miles, and my first BMW. Automatic/Thermostatically controlled dual-zone HVAC system.
This new-to-us car has, since we bought it, tended to have a midrange-pitched "rrrrr" sound that seems to increase or decrease with Engine RPM's when you're using lower blower speeds where you can hear it do so. You can clearly hear it with the car idling while seated in the interior, and cruising at low speeds in town.
When I found in the Owner's Manual how to shut the HVAC system off completely, suddenly the "rrrrrrrr" sound went away too. Virtually as silent as the inside of a bank vault. Now mind you, at-speed the sound is very minimal and doesn't increase with blower speeds which, BTW, all blower speeds function normally and without any overt and unusual noise; and all HVAC functions appear to work flawlessly. It's simply in-town driving that this a nuisance to an otherwise very, VERY quiet car...and is engine RPM related (alternator speed?). The sound seem to be coming from the front/dash.
This sound in question does NOT increase with higher blower speeds.
If my description is easy to understand, is this sound normal for these cars, or is it the early stage of a failing FSU? I see it's a fairly simple DIY replacement part, and I'd rather replace it before I lose blower speeds or the battery gets drained.
Thank you so much.
Last edited by 1BlinkGone; 03-25-2019 at 04:28 AM.
My guess it is the alternator....
Have a read of the first post of this:-
https://www.bimmerfest.com/forums/sh.../422191?page=5
Then skip to post 45 for the fix.
(You don’t need to remove the radio/OBM to remove the IHKA unit - just use plastic trim tools to lever it out)
If cleaning the IHKA sampling fan works, that will be great, but the system blower fan itself can also be the source and it's a bit more trouble (and $) to replace. I've noticed the rpm-dependent whine only when I have the AC on. Was told by one mechanic to have the AC refrigerant recharged first and see if that halted it. So far just living with it as I only use the AC a couple weeks out of the year.
Thank you for your post and I understand what you are saying. With that, the sound I'm hearing has nothing to do with the blower itself, or its speed. Best as I can tell - that sound is originating from behind the HVAC panel, and isn't in sync with the blower speed at all. Thanks again!! This is a fantastic forum and thank you all.
Last edited by 1BlinkGone; 03-27-2019 at 12:25 AM.
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