Very loud compressor-sounding noise in dashboard when HVAC turned on - see video

[gsxrken]

2003 540 M Sport

My car developed a sudden and alarming noise this afternoon.
https://youtu.be/E5AGMg2fYS4?feature=shared

As soon as the HVAC system is turned on, that noise begins. As soon as the fan speed is lowered all the way to turn the HVAC Off, it stops. The video is with the key ON, but engine not running. It’s the same whether the engine is on or off.

Any ideas? Tried searching, but only finding complaints about the small buzzing sampling fan. This is “big” noise and the vibrations can be felt in the steering wheel, dashboard, and even through the seat. Sounds like when an air compressor kicks on and begins to labor as the pressure builds.

[Ed CT]

Key "on", engine off, I'd say it's your HVAC fan motor skipping gears or hitting the housing.

Either that or someone's punking you by hacking your radio and playing a Pileated Woodpecker sound byte thru your speakers when the HVAC system is turned on!

[gsxrken]

It just seems like so much more than the baseball cards in the bicycle spokes sound a bad fan can sound like. And there was no warning.
But… what else can it be really.
Checked on YouTube and looks like a crappy job!

[Ed CT]

Someone on the board here (GearGrinder?) did the dash removal to service the HVAC fan, and IIRC he had a write up on it. You may also want to check under the dash first to see if there's an actuation door that's jammed and trying to open/close. What does it sound like from the engine compartment? If it's coming from the fire wall, you can remove the two ventilation ducts and listen more closely to the exact location. Maybe you can even shine a light in there and see if anything is loose or jammed.

[JimLev]

Sure sounds like the squirrel cage fan is hitting something.
As Ed said remove both air ducts from the firewall.
IIRC with the outside air enabled on the HVAC panel the “doors” for the air intake will be open. You can see and spin the squirrel cage fan.

[BimmrMeUpSnotty]

Sounds like something broke loose and is sitting against the fan and the housing. Taking the dashboard apart is actually very easy, but I have never had to go deeper like as in pulling the HVAC box apart.

[gsxrken]

Thanks that's helpful- I'm going to try to put eyes on the squirrel cage.
BTW- the AC on this car kicks ass. I think the fan moves more air than any other car I have ever owned. Amazing.

[BimmrMeUpSnotty]

Yep! The fan in these cars think they’re turbine or something.

[gsxrken]

So, after getting very familiar with my 540's innards, I've found that the fan has six broken vanes. Issue is, I can only find and fish 5 of them out of the bottom of the fan housing. My question is, are there are flapper doors or actuators down there that the missing vane (and the small outer ring bits that used to connect them) will jam up?

I'm thinking about installing the new fan, temporarily reconnecting the HVAC control panel, and reconnecting the battery to make sure the noise is gone before I spend 3 hours putting everything back together. I am not sure that the fan was the noise, b/c when I got to it, I could spin the squirrel cages without any noise even though one of them was missing 6 vanes. Right now I suspect the broken vanes were jamming something below the fan. (Just a theory at them moment).726433

[Ed CT]

Hmm. All six missing from the same side would cause an imbalance at speed and maybe wobble the fan into the housing or other nearby thing. So, yeah, good idea to pre-run the fan prior to re-assembly.

Got a boroscope camera to look around in there for the other broken pieces? They could be jamming up something else. There are some cheap ones out there (Amazon, Harbor Freight).

[gsxrken]

New fan runs smoothly up to max speed. No noises! Buttoning it back up.
Bought the BMW fan $$$ over the 1/2 price aftermarket ones b/c I don’t want to ever see it again. (The poster of the very good YouTube I watched to help with this job mentioned in the comments that he had to do the job again 8 years later due to fan failure).