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  1. #1
    Boris
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    finally back with perplexing air con issue

    after a long sleep '93 850 is back on the road. New brakes, headliner, plugs (even #12), rotors, caps, tranny and differential service, radiator, tires, drivers door handle, seat release handle, belts, tensioners and pulleys. Lot's of help from you guys and archives, but now I am stumpted. After replacing belts, tensioners and pulleys I recharged air compressor/conditioner and all was fine. Cycled on and off and had good pressure and cold air. An hours later drove off and turned on air and car temp gauge started moving towards high zone. Shut down and turned on heat and gauge moved to normal operating temp. Towed home and notice that when air con is turned on the air compressor pulley didn't want to turn and belt squealed and fan blade barely turned. Can turn the pulley by hand but when belt tightened, not too much, it won't turn. Fiddled with the tensioner and pulley and no problem with just air (fan on) but once air con turned on belt squeal reappeared.

    Thought there was a lock sensor that prevented this from happening to keep H2O pump working. Might be the compressor or clutch, but with it being able to be turned by hand but not by belt has me stumped.

    And I have searched the archives and found no similar situation.

    Thanks in advance.

    Boris

  2. #2
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    Member No: 89637 mlweaver is an unknown quantity at this point mlweaver's Avatar
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    Re: finally back with perplexing air con issue

    I'm no expert, but everything seems to point towards a compressor failure - including failure of the lock sensor. Could you have overfilled the system so much that the compressor can't turn?
    Good luck
    Mark W in mid-MO
    2008 335xi coupe
    1993 850Ci 6-speed

    2 turbos ..................or 12 cylinders, no waiting!

  3. #3
    dusty21
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    Agree - and there are 2 types

    of compressors and lock sensors.

    1) The new and replacement compressor has a larger diameter pully,
    a longer fan belt, and a replacement "lock sensor" that does
    NOTHING because the new compressor does not send a pulse. (Both are sold seperately)

    2) The older compressor, such as I have on my -91 850, has a
    smaller pully, smaller belt, and the original lock sensor that will shut off the compressor if it locks up (until you shutdown and
    restart the engine)

    You may have a bad compressoror, or overcharged.

    Check the fan belt size against realoem.com or some other source.
    If you have the large belt size, then, you probably also have the
    new "do-nothing" lock sensor


  4. #4
    Boris
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    Re: Agree - and there are 2 types

    I believe I have the original as I uses OEM to get the part number. Both the pulley that the belt is attached to turns by hand as does the inner clutch(I assume). The pulley that the belt is attached to is a little stiffer but turns and the outer turns quite easily. So this doesn't seem like a seized compressor. The belt and tensioners seem fine as all is working without engaging air conditioner.

  5. #5
    dusty21
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    Re: Agree - and there are 2 types

    The later model e31's all were equipped with the larger
    pully compressor and no-lock sensor. I guess they figured
    the larger pully would prevent belt failure - there were
    so many complaints about the A/C shutting down when water
    splashed up on to the belt on the older models.

    I do not know the date of change '93 to '95 ???

    By the way, a larger mounting bracket is qalso required when installing the new replacement compressor.

  6. #6
    Boris
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    Re: Agree - and there are 2 types

    Mine's a late '93. Still hoping compressor is good. Am I remembering correctly that the clutch engages via magnets. If so, could that be the problem? Given everthing turns without any difficulty seperately.

  7. #7
    Boris
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    Solved!

    Decided to compress the tensioners more and once it was compressed about half way the air compressor kick on and blew cold air with no belt squeal or slippage. Guess I didn't compress the tensioner enough, but sure thought the belt was tight.

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    Tensioners need to be ALL the way to the end, not

    just "halfway", according to the BMW Manual....

  9. #9
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    well that's good news!

    Thanks for posting your results! Enjoy the car.
    Mark W in mid-MO
    2008 335xi coupe
    1993 850Ci 6-speed

    2 turbos ..................or 12 cylinders, no waiting!

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