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Air conditioning hum.

Discussion in 'E39 (1997-2003)' started by bluewagon, Apr 5, 2010.

    • Member

    bluewagon

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    When I turn my air conditioning there is a low hum. I am blowing cold air. The sound seems to be coming from behind the dash.
    Any ideas?????
    Yes we need air conditioning now in Florida.
    bluewagon

    nilscnelson guest

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    AC Noise/Hum

    I have the same issue with my 545i but it sounds more like a "groaning" noise. I thought it was the AC compressor bearing, but my dealer assures me it is not. They claim this is a "normal" sound. I am concerned as my CPO warranty runs out in a few months.

    Anyone else have some thoughts???
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    MGarrison

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    For anyone who might actually know, car specifics are helpful (year, model, month of mfg, etc).

    Since I don't have experience with your models, all I can suggest is perhaps a blower-motor issue, or a motor involved in manipulating something with the airflow, or some such. Perhaps peruse realoem.com and see if it shows anything you might find suspect related to the a/c system, fans, flaps, etc.

    cwbiii guest

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    yet to own...

    I have yet to own a BMW that did'nt have some kind of noise when the fan was running at low speed... It can be just about anything. A bug that crawled down in there and died and the fan is making light contact. A leaf, apiece of paper. Unless it is loud or particularly annoying ignore it because it is unlikely to be a real issue. There are a lot of faint noises going on in these cars if you take the time to notice. Since some use active noise cancellation to help quiet the cabin then sometimes there are faint ticks and swishes related to this and that may very well be what we are hearing as it tries to adjust the cabin acoustics for different positions of the fan blades. One particularly annoying example of this is when you open only one rear window and the cabin has a low frequency resonance that doesn't go away until you open another window on the opposite side of the car. That's almost certainly the active noise cancellation at work that out of its range to adjust for.

    Chuck

    nilscnelson guest

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    AC Noise/Hum

    Thanks Chuck and MGarrison. I am new to posting and communicating on threads, sorry for not providing more info on my particular vehicle. It's a 2005 545i with auto trans, sport pkg, and premium pkg., just turned 69k miles. Not sure of the build month.

    Chuck - Good input, I'll ask the dealer to clean out any debris in the system that could possibly cause the issue. A lot of good info from you that I wasn't aware of let alone knew was part of my car!

    MGarrison - Didn't even think of the ancillary parts of the AC system, i.e. your comments on flaps, blower motor, etc. Will bring this up with dealer as well. Just assumed compressor and gave it no further thought.

    While composing this message, I just remembered that this dealer here in Jupiter, FL is the 2nd location for the BMW franchise. Maybe the techs/writers in this branch are not as experienced? Just a thought. I'll continue to live with this issue for the time being, but will have the whole car checked again prior to expiration of the CPO warranty.

    Thanks again Guys! What a great way to get unbiased and solid input from the Bimmer fraternity!
    • Member

    MGarrison

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    Any automatic-anything climate system in a car has got to involve motors or something to do stuff that you'd otherwise do yourself. My '87 E30's system is simpler - except for ports to direct air towards the mirror-view section of the doors which can't be closed off, all the other vents and air direction is done manually. 3 slide levers to open and close flaps to direct air towards your feet, face, or front windshield, and the dash vents move up and down by hand, and have a thumbwheel to open and close airflow. There's a quasi-complicated multi-stage switch for the blower fan (1-4 levels of speed/airflow), an a/c switch for the compressor, and a recirculate switch which closes flaps on the blower box.

    Every BMW hvac system since is more complicated - partially or completely automatic, individualized heat or cooling for either driver or passenger, with motors controlling functions we were doing manually 20 or more years ago, and then some. In theory you should be able to set-it-'n-forget-it and it'll do what you want depending on what buttons you push or settings or whatever, depending on how well the system's designed and works. Theoretical ease and convenience comes at the cost of more complexity with the potential for more problems.

    Hope it gets figured out and resolve, whatever it is!

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