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Z3 Crazy A/C question

Discussion in 'E36/7 Z3 (1996-2002)' started by chrissokol, Nov 11, 2010.

    chrissokol guest

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    For any/all that may be able to offer help:
    Car = 2001 BMW Z3 2.5L (automatic, yep the wife's car)
    production month 8/2001
    ~66,000 miles

    Here's what happens:
    1. Start car, turn on A/C (or it may have already been on).
    2. Compressor does not kick in.
    3. Rev up engine, compressor still does not kick in.
    4. Drive around normally, compressor still does not kick in
    5. Accelerate quickly from stop or slow roll, A/C compressor
    not only kicks in, but stays operational for the rest of the drive.
    6. After stopping the car and restarting, the A/C may or may not
    work, but if it doesn't, just accelerate quickly and TADA! she's on!
    Nutshell, A/C works fine once it starts. But takes a heavy foot to
    get 'er going.
    A. Compressor is ok, there are no mechanical failures
    (and all other parts of the system work flawlessly once engaged)
    B. Freon level is OK (I suspected low level, and added a little)
    I figured if the pressure sensors were low, they would then function
    normally once topped up a bit, and if the pressure was at the top end
    causing it not to work, then it would stop working alltogether if I added
    enought to toss the pressure over the top.
    My adding freon didn't change this erratic behavior at all.
    C. Electrical circuit is (mostly) intact, otherwise it would never work at all.
    D. Belt and tensioner are in good shape and have normal indications.
    I would like for it to work all the time without having to accelerate wildly
    (despite how much fun it really is, it's giving the wife a frownie face in the
    I have a multimeter and am ready to test away! Thanks in advance for any
    direction that can be offered. (oh, and links are appreciated if there are any
    long procedures)
    • Member


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    A few things to check.

    Start the car. Turn on your AC (go to MAX AC), and turn the fan all the way on.

    Go to the front of the car and look through the front grilles. The front condenser fan should be turning. If not, quite likely either your condenser fan is bad or your aux fan resistor is shot.

    Something else you want to check is to see if your ac compressor is engaging. If not, your AC compressor clutch is probably on its last legs.

    When the AC turns on, does it blow strong or weak when the fanis on the maximum setting?

    willconltd guest

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    The only moving part in your A/C system is the compressor. My first thought would be to look at the compressor clutch. Maybe the increased RPM helps the clutch to engage? Sounds strange to me, so just throwing that out there.

    Whats the vent temperature? Whats the ambient temperature?

    Also, if you have added too much 134A refrigerant you could easily decrease the cooling of your car. What are the high and low side pressures @ 2000 rpm? Too much refrigerant will keep it from cooling, and my experience has been it can also blow out one of the O-rings causing all the Refrigerant to leak out.

    This is pretty close to normal for Z3.

    Does your blower motor work fine in the car?

    If the compressor is fine, then I would check the sensor on the dryer. When the sensor doesn't detect any refrigerant, it won't let the compressor kick on to keep it from burning out. The dryer is on the left side of the engine bay in front of the washer bottle. Any chance something may have damaged the wiring to the sensor?

    SAFETY PRESSURE SWITCH 1 64538362055 $95.58

    So when you are accelerating wildly, it starts working, and then does it continue cooling while driving at low speeds afterwards? If it doesn't work at low speeds, then it could be the pusher fan, but that doesn't add up to me. You can see the compressor kick in if you are watching it while running the AC at idle.

    Whatever you do, don't use any of the stop leak stuff. Its the death of a Z3 compressor.

    chrissokol guest

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    Hi bcweir, and thanks for the speedy response.

    The electric fan by the condensor comes on immediately when the A/C button
    is engaged. It comes on even if the compressor does not kick over.

    The compressor does engage under hard acceleration, and then stays working for as
    long as I wish to drive after it engages.

    The interior blower fan is strong, and after the hard acceleration (the only thing
    that seems to get my compressor to engage) the A/C blows very cold, even when
    at idol for long periods (traffic).

    Any other thoughts?
    • Member


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    So much for that idea. give willconltd a shot at this issue.

    Thanks for the response though.

    chrissokol guest

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    Hi willconltd,

    My first thought was also that the compressor clutch was bad, but
    there was no noise whatsoever, and once I accelerate wildly one time
    the compressor works for the entire rest of the ride... even at in
    long periods of idle (traffic). The wife drives between 1 and 2 hours
    (in traffic) to her class, and after the first time she guns it out
    of a stop sign, she's good to go for the rest of the ride... but if
    she goes easy on it, the A/C will fail to come on for the entire trip.
    Pretty strange. Feels like a flaky wire or relay.

    I didn't measure the vent temp when the A/C does engage but it
    will freeze us out of the car. We have to turn the fan all the way
    to the lowest setting. I'm gonna guess 55 or 60 degrees.

    I agree with you on the pressures. I am not certified and don't
    have the guagess needed, so I will have to drop it by a shop to check
    the high and low side pressures. I knew that too much pressure could
    be bad, so when I added freon, I only added about a fourth of one can.
    I had just hoped to get it to act differently... it didn't.

    On the safety pressure switch, that sounds like one of the main
    remaining suspects. I am sure that I can't swap that without venting
    the system, so I will have to have a shop check it out an swap it if

    I don't suspect any system leaks as the system was intermittent
    even before I added a touch of freon. If the system drained, I would
    not be able to get it to work at all.

    Thanks and let me know if any other thoughts hit you!

    • Member


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    It's a popular misconception that a clutch has to make noise to go bad.

    The truth is that this is not always the case. A clutch CAN go bad without making any noise whatsoever. I'm not saying this is the problem with yours. I'm saying don't be deceived into thinking that just because you don't hear "noise" that yours is fine.

    The good news is that your AC compressor DOES work -- for now. The problem is that for some reason, you're having to force it to do so. That's not good for your compressor or the rest of your AC system.

    I recommend that you visit an AC professional as soon as possible.

    Again, I"m not saying that your clutch is bad. I'm saying it doesn't have to make noise to be on its way out. I'm also saying that continuing to run your AC system like this without fixing it COULD make this problem a lot more expensive if it's not corrected.

    willconltd guest

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    There is nothing you can't diagnose that an AC professional will be able to. Any auto parts store sells a gauge kit for AC systems. Generally the AC professional will throw parts at it till something fixes it. I learned this the hard way, and sad to say thats the reality.

    While the BMW dealer my have a way to test the sensor, I don't think there is a way to test the clutch.

    There is also a temperature switch on the compressor itself. I assume to tell it when to turn on and off.

    64528375442 $79.43

    You can replace the clutch and bearing separately from the compressor. I haven't found the part number yet, so you may want to look into that.


    You can replace the clutch wiring and bearing etc without opening up your AC system and having to recharge it. So I would ask around to see what shops would charge, and then weighing whether or not you feel like doing it yourself.
    • Member


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    Are you able to travel to his house to help him fix it? If not, don't take chances.

    I'm not sure if you understand the challenges of trying to diagnose something over the internet. Or in assuming that everyone has the same mechanical and DIY skills that you do.

    But to assume a professional will just "throw parts at it" until something fixes it does a disservice to honest, fair professionals who do this for a living (not me, certainly). You might as well be telling the person that a trained professional would cheat them.

    Especially if you're not there in person or willing to go there in person to see and hear what's actually going on.

    Servicing an AC system isn't the same as doing a tuneup, and you seem a little too eager to pronounce the problem to be a bad clutch or bad temperature switch without actually being there. This guy is going to be understandably upset if you have him replace the clutch and switch and not solve the problem. I would be too if I spent money on parts that didn't fix a problem.

    The other danger is that you're asking someone with an unknown level of mechanical experience to go tinkering around with a air conditioning system. That in itself is pretty reckless. R134 refrigerant is classified as a hazardous material and can cause painful chemical burns. That you're suggesting he do any kind of wrenching at all in or around an A/C compressor without knowing his level of mechanical expertise is taking unnecessary chances with his safety. You're not clairvoyant and you don't know what could happen.

    Disassembling or removing a compressor clutch may seem easy for you, but assuming he has the same level of mechanical experience you do isn't putting his safety first.

    If you're not willing to make the trip, don't be ashamed to get him in the hands of someone more experienced.

    chrissokol guest

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    (I want to thank both bcweir and willconltd for continued brainstorming!!)

    bcweir, I believe you are right that the compressor clutch can
    fail and not give me indications. And I suspect that I may need to
    follow your advice and take it to the professionals (considering
    how little time I have).

    willconltd, I hadn't thought about buying my own guages. I am a
    bit of a tool head and love to have the right tool for the job. I
    will check that out and see if I can pick up a set locally for a
    reasonable cost and see if I am actually in the right pressure zone.

    I tested the temp switch and it passed current through it when I
    tested it. I guess it works at least most of the time (but I can
    kinda make that assumption for every part in the system considering
    that it works some of the time)

    I also looked at the front of the compressor to see what would be
    involved in removing the clutch and just replacing it. But when I
    looked online at RealOEM it does not mention a separate clutch part
    number. I fear it is one of those compressors that you can't change
    the clutch on... we all know that means bigger bucks.

    Question for anyone: CAN A 2001 Z3 COMPRESSOR CLUTCH BE CHANGED

    back to bcweir, I totally know how difficult it is to troubleshoot
    as we are doing (online), and my mechanical ability far outweighs
    my electrical ability. I really need to get cracking on it.

    As far as throwing parts at it... I actually don't mind, especially
    when I can swap them out myself and save on both the labor and the
    parts markup. The way I see it, if there are 10 parts that can fail
    and I can buy and install them all for less than the cost of one shop
    visit, then at least I know all the other parts are brand spanking new.
    That gives me the warm fuzzies at least that the new parts shouldn't
    fail in the short term (fingers crossed). It makes the journey longer
    but in the end, I know more about my car. I'm cool with that.

    I have been rooked by workshops in days when I was not so saavy, and
    have been doing my own repairs for the past 25 years. I continue to
    have trust issues with workshops... I hope that can change. I have
    taken cars in with problems I have personally confirmed just to see
    what shops say, and I am constantly amazed at the GOOD parts the say
    I should change that have NOT failed or worn. I just don't trust
    them yet.

    I appreciate the concerns of both bcweir and willconltd for their concerns
    about both my safety and the environment, and I want you both to know
    that I mainly approached this forum as I know only real BMW enthusiasts
    are here and not the standard Ford or Chevy guys (not that we don't like
    them too) but just that we all here have at least some experience with
    the outstanding German engineering.

    My hopes are that someone else here will have a similiar experience or
    at least cover an area that I (or we) have not yet considered. So
    please continue to ponder and brainstorm for anything that hits you
    and I am thrilled to check out another facet of my Z3 (my first E36).
    • Member


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    While Realoem.com does not list the clutch as a separate component...

    ...you probably COULD replace it yourself without buying a new compressor.

    Quite likely you're going to need a special tool to hold the pulley in place while you remove the magnetic clutch.

    It's also highly adviseable that you acquire a Bentley manual to guide you through the procedure. Although my Bentley describes the procedure for removing the clutch from the pulley, my M70 engine uses a completely different design of compressor that likely would not resemble yours. Bavarian Autosport lists a Z3/M coupe through 2002 manual for $89.95.

    I have also found other information located here

    The instructions are not specific to your car, but seem to offer approximate instructions for removing the compressor clutch from your vehicle.

    If you want to order a compressor clutch, what you may have to do is identify the maker of your compressor, as well as the part number, serial number, or model number for your car. Then check online for the appropriate parts.


    chrissokol guest

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    I see the allen bolt that goes through the center of the magnetic clutch from
    the front of the compresor, so something comes off the front.

    I called around to my local import parts guys and they can't even get the
    compressor! They all said "go to the dealer". First of all, I don't buy that
    for one hot minute. Second of all, I wonder if there is a law due to the
    environmental concerns that wont LET those parts guys sell A/C parts
    that could cause illegal venting.

    I already have the compressor number 64 52 8 386 650 and will have to get
    a good look at the clutch to see if I can locate a number on it.

    I think I will pick up that Bentley manual... of all the repair books I have ever
    seen the Bentleys really do the best job. Chilton and Haynes do a horrible
    job of the individual specifics of a particular vehicle... I won't ever buy a one of
    those again, but Bentley I will consider EVERY TIME. They are outstanding.
    • Member


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    Nothing illegal about changing the clutch, but manufacturer probably had other ideas

    Some are worried about potential liability if someone tries to do their own servicing, gets hurt, then wants to sue the manufacturer for their injuries. Others would probably like to sell you a new compressor instead of the smaller profit on the clutch.

    As for the comments about the Bentley and Haynes manuals, it's no contest. I have actually owned both, and it's Bentley, hands down.

    My Bentley manual for my E32 750iL is 976 pages in length. I joke with people that it's called a Bentley because it weighs as much as a Bentley vehicle, but seriously, I wouldn't have it any other way.

    I'm pretty sure you're going to need that pulley hold down tool to keep the pulley from moving while you remove or reinstall the clutch.

    You probably only need to know the part number and maker of the compressor. Quite likely, both the clutch and the compressor will come from the same company.

    90 percent of the stuff you could need to do on an E32, Bentley will explain and show it to you.

    willconltd guest

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    Your motor is the same one as in the E46. So I would search for M54 instead of Z3.

    What I have found is a few things here and there, and I found this about replacing a compressor.



    So there is hope.

    The compressor should come off with a 10mm socket, and then there is a snap ring inside. I could be wrong, I am working from memory.

    I would attempt to avoid purging the system, because that adds work and complexity that you may not need. You can get gauges and a vacuum pump from harbor freight on sale for around $100 if you have a coupon and hit a sale.

    I am seeing more failures of the compressor clutch as I search the web.

    willconltd guest

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    Ok, clearly I am not thinking straight. I have a Bentley manual in each car.

    So the Bentley manual says to pull the fan and shroud, then use a strap wrench to hold the pulley in place. Then to remove the M8 bolt and then pull the clutch off. Sounds pretty simple doesn't it?



    Go Nuts.

    willconltd guest

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    Strap wrench is like 5 bucks at the hardware store.

    chrissokol guest

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    Thanks willconltd! That does look exactly like my compressor, and yes I do have the M54 motor.
    I am certain that I can do some investigative work without ever taking the compressor off.
    I can easily get to it from below without taking anything off the car but the belt. I love the strap wrench
    idea to hold the pully still. Mine has 3 large rivet/pins on the front I was going to hold firm with a flat
    shafted screwdriver, but that strap wrench sounds like a better idea! I may do that just to see if it is
    possible and get a part number off the clutch (since RealOEM does not list it).

    It may be a week before I have time. Thanks for the shots of the manual!

    superdave2002 guest

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    Did I miss it?

    I didn't see discussion of testing the clutch.
    Do you have current to/at the clutch at idle, and is it correct.
    Have you checked continuity of the clutch. ( it's an electro-magnetic coil) I don't have Specs, but the resistance should be low, it's a coil.
    Is the "air gap" correct. Clearance between the coil and the clutch plates.

    Just a thought: excessive "air-gap" plus added voltage from more rpm to overcome extra clearance equals clutch engagement.

    I would sure be mad at myself if I went to the trouble of removing the clutch only to find that it's not bad.

    Good hunting and good luck.
    Let us know the outcome,. A good puzzler.

    chrissokol guest

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    Hi superdave2002, thanks for joining in on my dilemma!

    I did try to put 12v on the clutch trigger wire, while running and while
    not running. I was unable to come to a conclusion because the clutch
    engages and continues working after one single hard acceleration. once
    I have "jumped off the line" (at a stop sign, or whatever) the A/C works
    just dandy for the rest of that journey (idling, traffic, or highway). So
    the clutch either works perfectly or does not even engage at all. Very
    black or white, no slipping, grinding, or squeaking. No audible indications
    that I have noticed.

    I have not actually measured the voltage at the trigger wire after I have
    gotten the A/C to engage. It is so hot down there within seconds of the
    engine starting, I have to keep my hands away for a good hour or two.

    I might be able to slip in an additional wire to the trigger wire assembly
    on the compressor and take a reading once I get the compressor
    engaged from a quick launch scenario.

    I think you may be onto something with the "air gap" scenario. If I have
    that magnetic collar loose or mal-aligned, those quick starts can be a reason
    for it to get knocked one way or the other, therefore allowing it to engage or not
    to engage. Sounds reasonable.

    On that same note, I have seen many flaky things happen when the voltage
    from the alternator is low or incorrect. I will have to check that out just to
    know where it sits. One more box to check and ideally rule out.

    And I'm not too mad if I change a part and wind up not needing it (as long as
    it didn't cost me too much). I am more disturbed if I don't get to a solution
    eventually. A little journey is not too bad... but I do want to hit that finish line
    at some point.

    superdave2002 guest

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    Check the voltage at the trigger wire before you get the clutch ingaged. ( No current.....Not the clutches fault)
    I'm not sure about your model, but a lot of cars will energize the AC clutch AND the aux. fan with the AC on and the ignition in the run position. Engine not running.

    And here's another question .....For you to find the answer to.
    Does your car have a WFO or wide open throttle AC interupt switch.
    Something we old timers did in the 70s to give us more power when we needed it.
    Some manufacturers picked it up in the 80s on small dispacement motors. A simple vacuem switch.
    You see my reasoning for the question?

    I'm sorry that I can't be more specific about your car. The newest BMW I own is an 89, and the newest vehicle I own is a 93. ( 300 Cummins with mechanical injection)

    I've solved more problems by asking questions than I have giving answers.

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