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Thread: 97 BMW Z3 a/c problem

  1. #1
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    97 BMW Z3 a/c problem

    *SOLVED*

    The car is a supercharged 1997 BMW Z3 Roadster 2.8L Automatic

    it has 32,000 miles on the whole car

    To start this off, i have searched high and low for fixes to my problem but so far nothing has come up.

    So the problem is the air conditioning does not come on when the Snowflake button has been pressed.

    The car has the manual (round) knobs.

    As far as i could remember the A/c worked just fine, The car is supercharged and has a Spal Auxiliary fan that started this whole thing. The fan was installed by a mediocre electrically inclined person and down the line, one of the wires had shorted out and was popping the fuse in the fuse box in the engine compartment. A family member unknowingly put a heavier duty fuse in place of the fuse that had blown and caused some wires underneath the dash to melt causing all sorts of problems. another family member removed the passenger jockey box and replaced as much of the bad wiring as he could find (this family member is very electrically inclined). after the wiring was replaced...no more a/c.

    i wanted to start at the a/c compressor and work my way back to the snowflake button in the dash.

    we started with the compressor itself. with the engine running, the snowflake button when pressed, illuminates. when the button is pressed the interior blower motor engages but the compressor never does, hence no cold air. if the relay is removed from the engine fuse box and the power terminals are jumpered (i think number 85 and 30 on the relay) the a/c clutch engages and cold air is produced.

    I figured the compressor is good as it works as normal when power is supplied
    The a/c was charged professionally so i know that it has a good charge and is not leaking
    the relay is good as i have tested it and have tried a new relay in its place.

    the relay itself is waiting for a ground so it can provide the compressor power. as far as i can see, the ECM is in control of when the relay is grounded as long as a few stipulations are met (pressure sensor, aux fan, stuff like that) so i traces the wire from the plug on the relay all the way back into the interior of the car and everything seemed good. i ohmed all the wiring as well as did continuity tests on everything leading back to port 74 on the ECM ( the port that controls the ground). everything i could see and reach tested fine.

    when the a/c button is pressed, the ECM ideally should go through its checklist to make sure the system is ok, and when it does, it will ground the relay turning the compressor on but it never does. the ECM never grounds it just gives a constant 12 volts.

    The Aux fan has been wired correctly and i know that the normal and high speed relay are part of the variables in the ECM checklist, they are all functional.

    The Evap controller is good, The evap temp sensor is good, the recirc assembly seems funtional as everything else works. the only thing that i know is dying is the temperature switch on the side of the radiator but unless the ECM is watching that for specific resistance, it seems like it was just a mechanical switch for the Aux fan but when jumpered (to simulate the temperature switch grounding under normal operation) has no effect.

    The only other thing i can say that might aid in the Diagnosis is that i have a buddy with a scan tool he picked up for a meager $20k. when he hooks it up to the car it says it cant communicate with the a/c system. he can see everything else going on with the car but not that. and i would imagine that could be a problem wire thats causing this but idk.

    im a bit lost as to what else i can do before i start tearing the dash out to check for something wrong...

    (i also have the Electrical troubleshooting manual and have looked and did a continuity test on every piece of equipment it showed that was in the a/c setup)
    Attached Images Attached Images
    Last edited by Neffly4u; 07-02-2017 at 07:48 PM. Reason: Resolved.

  2. #2
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    Although you say the AC has been charged and isn't leaking, I would strongly suggest you get it checked for gas pressure before anything else. Unless you start with the absolute basics you could be going round and round in circles.

    Also, a $20 scan tool will only be any good for reading obd2 engine codes and won't do anything else on any car, especially on the Z3 that has no aircon control module to connect to in the first place!
    Last edited by BladeRunner919; 08-05-2016 at 03:29 AM.

  3. #3
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    Quote Originally Posted by BladeRunner919 View Post
    Although you say the AC has been charged and isn't leaking, I would strongly suggest you get it checked for gas pressure before anything else. Unless you start with the absolute basics you could be going round and round in circles.

    Also, a $20 scan tool will only be any good for reading obd2 engine codes and won't do anything else on any car, especially on the Z3 that has no aircon control module to connect to in the first place!
    Thanks for the reply, just to clarify. I have an uncle that has one of the fancy a/c machines that you hook the car up, it discharges it, recharges and does a leak down test and everything came up fine.

    Also the scan tool I'm talking about he may have paid less for but it was $20,000 not $20 because it has a lot of diagnostic features to it. But it would make sense if it's saying it can't connect because there is no a/c control module...

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  4. #4
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    Go to the electrical diagram page prior to the one you attached. What is the voltage at point D? (pin 19 of DME when A/C switch is on and fan set to 1) Remember that the fan control must be set to "1" or higher for the A/C to come on.

  5. #5
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    Hi, I used to post on here , had a m roadster as my toy, it's gone now and I bought nice hell rot z3

    Question?

    Having issue getting voltage to Ac compressor, went through lots of postings and googling and done all tests I can find

    1. Compressor works when 12 VoLTE applied directly and jumper into pin 30 and 87 on relay socket, all diagrams say a pin 86b is not used but I have no female connector on pin 86 that is supposed to come from the end, the Ac did work but never blew cold,

    2. I do have 35 and 150 pressure with compressor engaged, fans do not come on without jumper sing them,

    He is my plea for help can some of you guys confirm pin 86 is not used on there z3? Here is a pic showing only 4 wires were there should be according to the diagrams on the web

    Can't post pic from phone but I was hoping someone on here would know what I am going through, basically I need power to the compressor

  6. #6
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    Where do I check pin 19 on the dme? Is there some connection point? , I am a new to reading these diagrams.

  7. #7
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    A/c button is depressed and illuminated (hard to see but it's blue).


    Pin #19 on the dme (plug d on the diagram) shows 13+ volts.

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  8. #8
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    Have you been following the other thread? I don't want to repost everything again here.
    http://www.bimmerforums.com/forum/sh...r-relay-pinout

    Post #13 has some information.

    You've verified that the logic for the controls is valid (pin 19).

    Now you need to verify that the pressure state is valid (pin 16).

    Are your pressure switches closing? With the A/C ON conditions met, check voltage going in versus coming out of the switch. It becomes input #16 to the DME from the Evap controller. A low or high pressure switch not closing will cause the DME to not start the compressor. Valid bar range is posted in the other thread.
    Last edited by Monolith; 08-08-2016 at 10:12 PM.

  9. #9
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    Ok guys. Really stumped at this point and need some advice as to where to go.
    I have read the wiring diagrams and have done a continuity test on EVERY wire on them. It all checks out.
    There is power to the snowflake button as it lights up when pressed.
    When pressed the blower motor kicks on low. And engine speed changes to accommodate but no compressor engaging.
    Aux fan does not come on when snowflake is pressed but does come on with the temp sensor reaching the 91c
    Pressures are good. Just had the freon professionally charged with 1.9lbs of freon and a leak test performed. No problems.
    A/c pressure switch is new and have tested with a multimeter. Switch shows proper pressure.
    Temp sensor new and kicks high and low speed fan on at 91/99c
    Literally have torn the whole interior apart and have checked every wire heading from the snowflake button all the way to pins on the DME. Really lost as to where to go from here.

    For reference. The ground wire for the high speed aux fan relay is not connected as I have an E fan instead of the mechanical fan so I have a separate relay but use the temp sensor as a trigger for it. Besides that everything else seems correct

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    Last edited by Neffly4u; 06-24-2017 at 03:55 AM.

  10. #10
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    Have you checked the relay?
    bmw-e36-relay-layout.jpg

  11. #11
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    I have swapped the "low speed fan relay" and "compressor control relay" and both relays worked to turn the aux fan on. So I would assume they both work

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  12. #12
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    Ok guys! I have an idea. I need someone to crawl underneath the dash and do a voltage test for me.
    Under the driver's side dash there is the Evap Control Module. I'll include a picture of it. I am wanting to see what voltage pin 5 produces when the snowflake button is both on and off. I'm only getting the 13v and there is no change when the button is pressed.
    It's s221 on both the diagrams.

    Be aware that pin 5 has +13v coming into it from the normal speed relay so I am looking for anything above 13v.

    Because the DME shows pin 16 as an Input, I'm assuming that this evap module sends a voltage to the computer telling it that all the other sensors and what not checkout. My only guess is the module does this by sending a higher voltage to the DME to tell it everything is good to go. If anyone understands how this might work different, let me know.


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  13. #13
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    For those of you who read this thread. I'd like to tell you...it's been resolved! It turned out to be the a/c control module mentioned in the last post. If you need to diagnose this. Try grounding pin 5 with the module plugged in and the system should turn on. We took the module apart and it was a bad fet on the board. Put a new fet in and its fixed!

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  14. #14
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    Thank you for updating. It's always good to have insight on fixing unusual problems.
    -Abel

    - E36 328is ~210-220whp: Lots of Mods.
    - 2000 Z3: Many Mods.
    - 2003 VW Jetta TDI Manual 47-50mpg
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    - 2016 Mini Cooper S

  15. #15
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    Quote Originally Posted by 328 Power 04 View Post
    Thank you for updating. It's always good to have insight on fixing unusual problems.
    This, it was a great post, good diagnostic skill, nice work soldering in a new FET to fix it. Only oneself would go to the depth of repairing a component inside a control unit.

    Having gone through A/C diagnostics on my E90, I was forced to understand HVAC systems in general, that was also an Evaporator issue, but relatively easy fix compared to this (EVAP expansion valve).

    “Great wisdom is generous; petty wisdom is contentious.” 无为

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