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That HVAC Sound...what is it?

Discussion in 'Model S: User Interface' started by Todd Burch, Feb 24, 2013.

  1. Todd Burch

    Todd Burch Electron Pilot

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    Hi guys. Try something out for me:

    Sit in your car, plugged in, and parked in the garage (I did this at 51 degF). Pause the audio so it's quiet in the cabin. Turn on the climate control with the fan set to 1. (In my case, I've got the blower directed to the windshield only, temp at 72 degF, Auto for recirc, and Auto for A/C, but don't think these settings matter. In fact, not even sure the fan at 1 matters).

    As the climate control starts up, do you hear that sound that sounds a bit like a faint, muffled compressor that slowly steps up to a higher frequency every 5 seconds or so?

    Question 1: What is that? I'm guessing the compressor?

    It is *not* the fan blower, because it steps back down and goes off (or to a very low level) after a moment, even with the fan at a constant speed. Is it the heat pump compressor? I'm surprised that it seems to step back down and go away fairly quickly.

    Question 2: As the compressor (as I'm calling it) begins its slow ramp-up, there is one "step" that it reaches that causes a large amount of buffeting/vibration in the cabin--very likely due to the fact that the cabin is sealed so well. Does anyone else hear this sound or is mine abnormal?

    Thanks for the input!
     
  2. aviators99

    aviators99 Model S - R140

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    Mine lasts more than "a moment", and it is a bit embarrassing for a car that's supposed to be so quiet. Sounds like a jackhammer in the frunk. Interestingly, if I cycle the climate control (turn it off and back on) it goes away for a while. Also, the sooner I start driving, the sooner it goes away. Maybe it's some sort of fan to allow the climate control to work when there's no air passing through the intake from motion.
     
  3. Todd Burch

    Todd Burch Electron Pilot

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    Actually, you're right. When I was testing it a moment ago, it went away fairly quickly, but yesterday I was going through a drive-through and it lasted over a minute. It's not a very loud sound, but the pressure/frequency makes it "feel" alarming. OK, so I'm not the only one.
     
  4. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Once you obtain a quiet by design car, as opposed to a quiet by muffling car, there are all kinds of ancillary system that create noises that are normally drowned out by the engine or the sound insulation. Of course, you could add sound insulation but most sound insulation a) is really heavy, and b) gives off toxic fumes when burning. The real answer is turning up the audio volume :)
     
  5. Todd Burch

    Todd Burch Electron Pilot

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    I get that Jerry. This is not a sound that would be otherwise covered up. It's a heavy vibration, like driving over a washboard road. It goes away after a little bit, but is more a vibration than a noise.
     
  6. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Ahh. Probably the only real solution for that is to have the pump/compressor mounted on some isolation dampers. Probably not doable until 1.5 or 2.0 Model S depending upon the room they have to work with.
     
  7. DrComputer

    DrComputer Member

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    It is the sound of the A/C compressor. Just thank yourself they didn't use the same one as they did in the Roadster. That beast is horribly loud. Also, there are three condenser units and two sets of air bypass louvers in the frunk and the system can bypass one or two of the condensers as necessary for the cooling output needed. Before Tesla changed the "secret code" is was fun to watch what the system was doing and relate the sounds that one would hear to the current mode.
     
  8. jhs_7645

    jhs_7645 VIN: #3305

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    Based on my conversation with Tesla service about the Brake vacuum pump, that *is* mounted on dampers, my guess is the AC is as well. They told me that the tolerances between the vacuum pump and the frunk lining are very close, and it seems like mine is very loud because the pump seemed to have moved, is touching the frunk lining and causing it to amplify the vibration. It's possible that some folks are having a similar issue with the AC? Not sure, just theorizing here.
     
  9. Blurry_Eyed

    Blurry_Eyed MS Sig #267, MX Sig # 761

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    I also think some of the sound is coming from the back of the rear seats. If you tap on the back of the rear seats, it reproduces that low bass sound that is happening with certain HVAC settings. It's also related partially to the pressure buffeting issue that the car has if the rear hatch shims are not set correctly. So it probably is a combination of the compressors, the back of the rear bench seats acting like a bass drum head and the rear hatch shim adjustment.

    My theory is that the airflow in the car moves in such a way when the vents are set in a certain position and the fan speed is set at a certain speed that it causes the rear hatch area to act like a big bass drum. It may be causing enough airflow in the right direction to cause a bit of a pressure zone between the space where the rear seats and top of the ceiling are. That space is relatively small and any small air movement moves the covering over the back of the rear bench seats and the big open space of the rear trunk is just like a massive bass port. Tap the back of the rear bench seats and you should be able to reproduce the sound even if the HVAC system isn't on.
     

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