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Thread: AC Trouble

  1. #1
    Join Date
    Mar 2020
    Location
    San Antonio, Texas USA
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    94
    My Cars
    1990 BMW e34 525i

    AC Trouble

    Hi,

    Do any of you know how to troubleshoot the AC system in a 1990 bmw 525i e34 step by step?

    Any help is appreciated!

  2. #2
    Join Date
    Apr 2019
    Location
    canby, OR
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    185
    My Cars
    1990 bmw 535i
    If its not turning on the first thing i would check is if theres enough pressure in the lines, i think theres a pressure switch to prevent from burning out the pump

    Sent from my LG-US998 using Tapatalk

  3. #3
    Join Date
    Dec 2004
    Location
    CT, USA
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    4,161
    My Cars
    e28, e34, e39
    What's the issue?
    demet

  4. #4
    Join Date
    Mar 2020
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    San Antonio, Texas USA
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    My Cars
    1990 BMW e34 525i
    There is enough pressure in the lines.

    - - - Updated - - -

    The clutch does not engage, and the fan only runs in the highest speed. I replaced the infamous "sword" resistor, but nothing changed. The resistor is in good working condition.

  5. #5
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
    Join Date
    Sep 2006
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    BFE
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    11,090
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    E34T
    How much pressure did you measure?

    The blower fan switch probably has bad contacts. Recommend disassembling and cleaning it. UPDATE: the blower fan and AC are separate problems.
    Last edited by moroza; 05-09-2020 at 04:31 PM.

  6. #6
    Join Date
    Mar 2020
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    San Antonio, Texas USA
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    My Cars
    1990 BMW e34 525i
    Will do!

  7. #7
    Join Date
    Sep 2006
    Location
    NW suburban Chicago
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    16,302
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    hiss by my window
    Is the clutch being commanded on? That is a typical symptom of too low pressure.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  8. #8
    Join Date
    Mar 2020
    Location
    San Antonio, Texas USA
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    My Cars
    1990 BMW e34 525i
    Here is an update. The compressor is always on. It cannot be turned off at the ac control unit. The only way the compressor can be turned off, is by removing the compressor’s relay. Furthermore, the fan speed only works on the highest speed. First, second, and third speed are not functional, only fourth.

    things done: I replaced the compressor relay, removed the ac control unit and cleaned it. I also replaced the fan motor resistor. My car has a sword type resistor.

    It seems to me, there is a short somewhere. I don’t know where to begin looking for the short. Any help is appreciated.
    Last edited by tyromechanic; 05-31-2020 at 12:49 AM. Reason: Used wrong word.

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