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Question E46 M3 - AC mystry and some questions

Discussion in 'E46 M3 (2001-2006)' started by mpower8, May 18, 2012.

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    mpower8

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    My car is 2006 M3 with 31k miles on it. It is driven well with some spirited accelerations :D but no tracking or drifting etc.

    I was hearing hissing noise whenever airconditioning came on - indicating lower freon (or equivalent).
    I was suspecting that there was leak in my system somewhere - BUT dealer found no leaks! They said that this is normal and just topped off the refrigerant.

    Does the system lose refrigerant and needs refill over time? I had no AC work done since I bought it new in 2006

    When is a good time to replace trans and diff lubricants and what brand/type is best for a M3?

    Thanks
    • Member

    eblue540 Fourth Gen Bimmers

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    On your cooling issue, you didn't mention it, but I assume you were not getting cool air and that is why you had the dealer look at the system? If you were not getting cool air, you must have had a leak if they added refrigerant to correct the problem. If you took it in just because it was hissing but you were getting cooled air, then they needed to do something to justify their charges for trouble shooting the system.

    Old school Maintnenance schedule for transmission and diff juice is every 30k miles, so you are due if not recently done. My Indy recommends and I use Red Line products in the factory specified viscosities for your car.
    • Member

    mpower8

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    Thanks eblue540.
    The AC was blowing cold but according to dealer it was less cold than normal (no clue!)
    But apparently when they ran through the testing of the AC (took close to 1.5 hours) they could not come up with anything. Service person mentioned that the machine evacuates all the freon and then does some type of leak and vaccuum test. Any insights here?
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    eblue540 Fourth Gen Bimmers

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    Sounds like they had to come up with something to tell you so they could justify charging you for that 1.5 hours of trouble-shooting and finding nothing else. Did you think the car was cold enough before you brought it in?

    Typically, if the refrigerant leaks enough to impact the output temp of the system, its all gone pretty much immediately and it blows hot. I think your system could be just fine. If the hissing was the refrigerant leaking out, it would have blown hot air immediately.

    A/C systems can make hissing noises during normal operation. The sounds that the A/C system makes may change as dampers open and close in the dash in response to changing temperatures or operating modes. Those are my insights. I hope it is all working OK now.
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    MGarrison

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    I think it's possible for car A/C systems to have any kinds of leaks - small, big, catastrophic, intermittent, etc. A perfectly functioning a/c system should not leak refrigerant, but if there is or are small leaks, they may not be easy to find. I would also think it possible to have some very minimal leakage over many years where eventually you get to a point that the refrigerant charge is down enough to not be cooling adequately.

    What the tech told you they did sounds like a normal a/c diagnostic test to me. Since the EPA has sat its fat regulatory @$$ on just about everything anymore, including car servicing, the days of just topping off a car's a/c refrigerant are long gone; anyone doing car a/c work has to use machines that capture the refrigerant. No more freon into the atmosphere and destroying the ozone layer (can't say I've heard anyone panicking about the hole in the ozone layer at the poles lately, I wonder if that situation is better, worse, about the same, or just faded from being newsworthy.. aaaanyway...)

    So... not sure about your noise, particularly without being familiar with it's normal functioning for your car - hissing sounds a little odd, but I would think that if you had an a/c leak that manifested itself by hissing so loudly that you could hear it, that you'd be out of refrigerant with no a/c in very short order, and, that it would be unlikely to audibly leak only when the a/c is turned on. It _might_ be that you're hearing the refrigerant as it goes through the expansion valve or circulating through the evaporator, but to me, that would seem a bit uncouth on BMW's part for their desired in-cabin noises for driver and passenger.

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