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Thread: Weird IHKR Problem

  1. #1
    Join Date
    Jul 2023
    Guayaquil,Guayas, Ecuador
    My Cars
    1991 BMW 316i

    Question Weird IHKR Problem

    Hello all, Im new to posting but I've been reading a lot here.

    I've a weird problem with my AC system since I bought the car. I've probably read all the topics here about it.
    I'm going to describe the problem and all the steps I've gone through.

    So, it's a 1991 316i with the analog AC controls, the compressor is active all the time.

    (TLDR: I don't really have an idea on why the DME is pulling the relay to engage the compressor clutch with or without the AC signal)

    The first things I checked:

    • Clutch is not stuck (Engages after a couple of seconds of the engine getting started)
    • Relay K19 (compressor is good)
    • Fuse 16 disengages k19 and the clutch disengages

    So far on the electrical...

    I suspected a bad IHKR,
    • None of the buttons would work at all, sometimes they all would come up, work (just the lights ie; pressing the AC switch would turn off the led, but that's about it) and then after some time stop working, compressor still engages always.
    • Pulled it out, and replaced the caps (some seem to have leaked)
    • No luck with that, got a new IHKR, same problem.

    I discovered that if I disconnect the IHKR completely from the 3 connectors, after some time, when reconnecting it and putting the key on ACC, I would hear all the flaps cycling and all the switch's LEDs would work again, this time if I pressed the air circulation switch for example I would hear the flaps close.
    Same for the rear defogger, I would hear the relay click, so my conclusion is that both IHKRs are "working".

    After a couple of engine cycles, both Air circulation and AC switches would stop responding all together

    Starting suspecting something between the DME and the IHKR

    Pin 48 from DME goes to Pin 4 on X20 and then K19 and enables the compressor, thats working DME is pulling that relay

    Pin 18 on X18156(black) from IHKR is the to be AC request that goes to Pin 6 on X20 and pin 86 on the DME
    I don't have a pin puller atm, so I tested continuity between them and open to ground, all good.
    I wanted to know if the IHKR was sending the AC request there is a terminal in between the IHKR and DME under te steering column, I tested it when pressing the AC switch on the control module it sends 10volts

    Decided to check on the DME and discovered some corrosion on the left side of the PCB right around where pins 85, 86, 87 and 88 are. Pinout
    85 A/C pressure switch input
    86 A/C switch
    87 Data Link Connector RxD
    88 Data Link Connector TxD
    WhatsApp Image 2023-10-01 at 9.45.24 PM.jpeg
    Being that the data communication pins where there it made me suspicious that that might be causing the IHKR to "deactivate" after some time.
    Clean them up, resoldered the header but the problem still persist

    At this point, I don't really have an idea on why the DME is pulling the relay to engage the compressor clutch with or without the AC signal

    If anyone has any pointers I would really appreciate them.

    Some things on my mind:
    Is is possible that the DME is programmed to always turn of the AC?
    Does the IHKR has some kind of self test on all the components inside the heater box and that's why it disables itself?
    I'm assuming the pressure switch is not important at this time because it should tell the DME what to do with the compressor after its being requested ON?
    WhatsApp Image 2023-10-01 at 10.14.25 PM.jpeg

  2. #2
    Join Date
    Jun 2010
    My Cars
    1997 328i
    I would suggest taking another look at the DME for cracked solder joints and oxide. After reflowing with some fresh solder with flux any suspicious joints then clean both sides of the board with Deoxit 5% and an old toothbrush, spray everything liberally and scrub, repeat. Deoxit is what you want don't use basic contact cleaner.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

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