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    mmmmmkay. There's at least two types of compressor fitted to the N52. With and without magnetic clutch. BUT, I think they're both PWM controlled (at the compressor), not CAN.

    https://www.underhoodservice.com/bmw...c-compressors/

    Here are the models that got the clutchless:



    and here are the models that got the clutch:



    the e85 has it's own part number, so who knows what's going on there:

    https://www.realoem.com/bmw/enUS/par...&q=64509182800

    BUT the clutch doesn't stop it from being a variable rate pump. The clutchless pump is always turning, but can vary the pump geometry so it isn't actually compressing. I think the clutch just ALSO disengages so the bearings in the pump don't wear, and that was added on the later models??

    Here's the thing... if the control is PWM I *think* we just need to know the voltage. If it's "off" the modulation is 0, and "on" the modulation is 100. Am I crazy?

    In earlier air conditioning systems, the compressor ran at full capacity whenever its cycling clutch was engaged. If the engine was running and the clutch was engaged, the compressor was pumping. And the faster the engine turned, the more pressure the compressor developed. The only way to modulate the pressure produced by the compressor was …
    Last edited by hubcapboy; 07-27-2020, 07:57 PM.

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      This is a different model, but still a BMW PWM compressor. I expect this is going to be the same frequency and voltage.




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        yeah I am pretty sure it's not just an on/off 12v, but maybe it would work? if it's PWM could you overheat the coil by supplying a constant 12v?

        regarding the MAF, you can't disable all the pins. You still need the IAT (signal and ground).
        Build thread

        Bimmerlabs

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          So. Last post about AC until the engines turning. I promise. I know no ones else cares about it ;)

          I’m just trying to determine if I can talk to the compressor without some serial connection I don’t understand. The alternator reports back to the DME in a language I don’t talk.

          If we assume that other reference is consistent with how PWM controlled variable rate compressors work (and other compressors on other manufacturera cars seem to work the same way) we can start figuring it out. As long as those wires connect to a coil and not some computerized controller, the resistance between them is meaningful.

          The info we have from the 7 series documentation above is 12v, 0.85A, 400 Hz. The frequency is almost meaningless. A coil doesn’t care if it’s driven by 400 or 600... but we can consider 400 a minimum (if it was 25 we’d be shaking the compressor to pieces, but at 400 it smooths out.)

          PWM is just a stand-in for variable voltage on a motor controller like this. If your supply is 12v and you turn it on and off 400 times a second with equal durations, a DC motor just thinks it’s being driven by 6v. If you turn it on and off 400 times a second with the duration 2/3 on 1/3 off, it sees the equivalent of 9v.

          If the coil was expecting to see 12v PWM with 99% on, 1% off and drew 0.85A, we’d expect its resistance to be around 14 Ohms. Well... it’s 11.2. By my monkey math that means we can certainly safely drive it with a constant 9.5V, or 66% duty cycle on the PWM driver. (I put 1.5v across it and didn’t hear it move).

          I’m going to pursue powering the compressor from the e30 chassis wiring, and controlling the demand with the PWM. I’m concerned that the DME control of the AC relies on other safeguards such as temperature sensors in the e90 dash HVAC (to prevent the evaporator icing up).

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            I care about it. I live in Az. Having A/C is only 2nd to being able to start the engine.

            But I have a different compressor, and I planned to pick up a Gpeterson CAN board. Hopefully one will be available. I was thinking having the hoses modified would be the biggest problem there.

            I wasn't able to see your alignment picture either. I have no idea 'where it ended up'. Was your block tilted, or did you already have it lined up?

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              Oh that’s suspenseful... they’re showing up for me so I didn’t know what the issue was. Here’s where crank centerline hits... our conclusion was that we’re about 1/4” off chassis centerline at the rear axle, but the engine wiggles enough on the mounts to make that negligible. It’s a big ratio between the width of the engine and the distance to the rear axle... this misalignment is 32nds of an inch at the front. I could cut and re-weld the arms and be wrong in the other direction by twice as much.

              The diff is offset from centerline by about 5/8" to starboard, so as the engine sat in my fixture, we were slightly more offset than factory... but over the roughly 36" between the U joints it's the difference between 1 degree of joint angle (factory) and maybe 1.25 degrees (current fixture alignment).


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              Edit for clarity: At the rear subframe, the string is about 1/4" to port, that is the engine is pointed very slightly towards the left rear wheel. Over a 101.2" wheelbase this is a misalignment of less than a half degree.

              The diff is offset to starboard (left in this photo, but right in the car)
              Last edited by hubcapboy; 07-28-2020, 11:55 AM.

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                yeah, the E90 HVAC relies on other sensors, including a humidity sensor, to run it. You definitely don't want to try to swap all of that stuff over (although it does work really well on the E90).
                Build thread

                Bimmerlabs

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                  The mounts on a n52 & m54 compressor may be the same, they look to be. As long as the belt lines up that may be an option to just eliminate the swash plate. You would still want a way for the dme to see the compressor signal for idle speed changes.

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                    I said last AC post!

                    Caperix almost ruined my surprise backup plan. The m54 compressor definitely looks like is a similar mount, but it’s driven off a secondary belt on that motor... so the pulley is narrower/fewer ribs.

                    but the compressor from and m73 looks promising...

                    For some reason, even though my father's 1998 BMW 750iL only has about 68,000 miles on it, the air conditioning compressor stopped compressing. Over a period of a few days, the car gradually started blowing warm air. After checking to see that the compressor was indeed engaging (to rule out electri
                    Last edited by hubcapboy; 07-28-2020, 06:58 PM.

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                      I bet you can swap pulleys. The only thing modern BMW loves more than cheap plastic parts, are cheap plastic parts that are interchangeable on multiple models.
                      Build thread

                      Bimmerlabs

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                        AC isn't going to lubricate your engine. How's the oil pan??

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                          Next update is oil pan. I swear. I’m done with AC (for now).

                          I won’t even work on wiring until I have a pan update. I promise.

                          Comment


                            OK.

                            Two oil pan data points for people to think about. There are two examples of fabricated oil pans for BMW inline motors that I've found. One happens to be for our engine:

                            https://www.bimmerworld.com/Engine/E...-Assembly.html

                            It's not cheap, it doesn't fit the e30 chassis (because it's rear sump) but it looks like a boxed out pan built off a thick flange with a larger capacity sump. If anyone can track down a photo of this pan from above we might learn something else, but I just thought it was interesting that 50% of the aftermarket fabricated pans for BMW that I can find are for this engine... honestly that speaks to the effectiveness of the original BMW designs and capacities (usually with some baffling installed) and means there probably isn't much to improve on if we stick close to the original pan shapes for front sump cars.

                            There is an example of a front-sump performance pan for the M10/S14:

                            http://the320i.blogspot.com/2011/10/...g-oil-pan.html

                            https://www.bmw2002faq.com/forums/to...my-s14-engine/

                            This is interesting for a few reasons... 1. I had no idea the M10 and S14 were the same flange. That's just surprising. Are they the same factory pan? If so, further evidence that BMW didn't see a need to come up with something special to track the engine. 2. The second link mentions that the pan is fabricated by Moroso (sold by VAC)... that's not insignificant because VAC makes a TON of race goodies, and Moroso makes a TON of pans. If there's an innovation or improvement that worth making, it's probably going to be incorporated here, and I don't see much that beyond what I'd expected... a tray to tuck under the factory windage tray to drain to a sump, a boxed sump with wings to make volume... and some pieces to mate the two together.

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                              Bimerworld talks about "...as well as an alternate oil pump pickup." Does that mean one or the other or BOTH front and rear pickups? Can dual pickups work on a stock pump?

                              I love that Moroso S14 pan and I hope that's your guiding light. Yours will obviously made of steel, which is easier to fabricate and will hopefully be more bash resistant. I like shallow, and I suspect they have some oil control gadgets in that pan like trap doors and such.

                              Comment


                                The M10 and S14 are closely related. the S14 is basically just a hopped up M10 with a 16v head. In fact, the head bolts onto the M10 block IIRC.
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