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Thread: A/C and Heat Question

  1. #1
    Join Date
    Dec 2010
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    1995 BMW 850CI

    A/C and Heat Question

    Hello,
    For years I've had issues with unwanted heat. A year ago I took out the water valve and yes it's internals were rotted. I then blocked off the hoses and had nice cold air but no heat when I wanted it. I finally installed a new water valve and auxiliary water pump today. The a/c works great when the auto button is selected and also throws heat when I dial it up. Both sides operate independently. Problem is when I select the footwell button I only get full heat out of the outlet regardless of temp setting. When I select the button with all three I get only heat out of the defrost and foot vents but cool out of the a/c vents. I looked at Frankie's troubleshooting http://www.frankies-bmw.com/8series/...ter_valves.php. I get 12 volts at pin 1 at the HCV. Continuity at pin 2 and 3. The valves operate when 12v is sent to each pin. So from my review of many posts I understand that the water valves do not entirely close but rather modulate to keep the core at a constant temp. So then the heater core is always hot but then mixer flaps control the distribution of hot air and cold? Does it now sound like a mixer flap issue? Thanks.
    Last edited by EricinConejo; 05-24-2019 at 06:31 PM.
    EricinConejo

    1995 850CI, 1959 Chev Impala, 1965 Cessna 172, 1986 Mustang GT, 2002 Mustang GT, 2005 Dodge Durango Hemi, 2016 Land Rover Discovery Sport

  2. #2
    Join Date
    Dec 2007
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    Dallas, TX
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    10,384
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    '93 850Ci- Daily Driver
    Mixer flap issue. Check the stepper motor and the linkages to those flaps.
    '93 850Ci - Mineralweiß Metallic

    2001 740iL - Titansilber
    ALPINA B7 -Alpinweiß III


    ...the price of cool ain't cheap!

  3. #3
    Join Date
    Dec 2010
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    1995 BMW 850CI
    Not sure. I looked down the drivers side center vent and the 2 piece flap is moving according to the IHKA manual. And both the left and right stepper motors are mounted firmly and I can feel them buzzing when they should be moving as when I adjust the temperature. What I can't figure out is the water valve, which is new and thumps when I apply 12v from pin 1-2 and 1-3. When I have the left wheel at full hot detent I get 0v across pin 1-2 and 1-3 as would be expected so the valves would be open. When I have the wheel at full cold detent I get 13-14v across two of the pins and only 9v across the other one. When I put both wheels at full cold but left one not in detent I get 13-14v across both pins. With this voltage one would think that the valves should be fully closed but there is almost definitely water flowing through as I can barely touch either hose going to the heater core and the temperature of the air coming out of the footwell and defrost fluctuates depending on engine rpm. I'm not an electrician but maybe there is not enough amperage going across the pins to keep the valves closed? If that is the case then maybe it is the control panel in the dash that is at fault. I've seen a thread where several people have had success when replacing this part. Any thoughts?
    EricinConejo

    1995 850CI, 1959 Chev Impala, 1965 Cessna 172, 1986 Mustang GT, 2002 Mustang GT, 2005 Dodge Durango Hemi, 2016 Land Rover Discovery Sport

  4. #4
    Join Date
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    1995 BMW 850CI
    Does anyone know of someone that rebuilds the a/c control panel in the dash?

    Update: I believe it is now either the in-dash control or the control box as I just placed 12 volts directly to the water valve and whichever side I put it on would blow cold out of all vents and the other side hot. I've seen posts where the control panel has been the culprit. Seems odd though as the connector puts out 12 or more volts but apparently not enough amps.
    Last edited by EricinConejo; 05-26-2019 at 08:53 PM.
    EricinConejo

    1995 850CI, 1959 Chev Impala, 1965 Cessna 172, 1986 Mustang GT, 2002 Mustang GT, 2005 Dodge Durango Hemi, 2016 Land Rover Discovery Sport

  5. #5
    Join Date
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    99 840ci Sport Indv
    This seems the same problem that Frankie had - he wrote all about it here:

    http://www.frankies-bmw.com/8series/...ter_valves.php
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


    My BMW Repair YouTube Channel
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  6. #6
    Join Date
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    1995 BMW 850CI
    What I can't figure out is I'm getting 12 volts at the plug when asking for cold but it doesn't shut the valves, but when I directly apply 12v to the pins the valves close fully. Not enough amps?
    EricinConejo

    1995 850CI, 1959 Chev Impala, 1965 Cessna 172, 1986 Mustang GT, 2002 Mustang GT, 2005 Dodge Durango Hemi, 2016 Land Rover Discovery Sport

  7. #7
    Join Date
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    99 840ci Sport Indv
    The valves have one common connection that is permanently connected to 12V (GREEN/YELLOW) - then there is a connection for each valve to operate it (YELLOW/BROWN - YELLOW VIOLET) - these are connected to the IHKA which switches them to 0V to CLOSE the valve.

    So, with the drivers temperature wheel set to the lowest setting you should have 12V on GREEN/YELLOW and 0V on the other two connections.

    With the drivers temperature wheel set to the maximum setting all three connections should be at 12V

    The two extremes of the drivers temperature are over-rides, MAX=Valves open, MIN=Valves closed.

    All explained in the last section of this:

    https://www.meeknet.co.uk/e31/E31_He...eplacement.htm
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


    My BMW Repair YouTube Channel
    My Current 840ci Sport Individual
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    My E63/E64 Repair and Information Website

    Chase - Heroes to a generation

  8. #8
    Join Date
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    1995 BMW 850CI
    OK, I've read both extensively but didn't catch that the voltage varies on pins 2 and 3 rather than pin 1. Understand that now. I will check. I don't think my problem is exactly the same as Frankie as both drivers and passenger side acts the same, not just one side. But I have a control panel and control module on the way so I can troubleshoot it more as I know the water valves function normally. Thanks.
    EricinConejo

    1995 850CI, 1959 Chev Impala, 1965 Cessna 172, 1986 Mustang GT, 2002 Mustang GT, 2005 Dodge Durango Hemi, 2016 Land Rover Discovery Sport

  9. #9
    Join Date
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    1995 BMW 850CI
    An update: Thanks to one of our members I swapped out the in-dash controller. Now, with the controller set to cold, when I connect the heater valve I can feel the solenoids activate. Yesterday I finally had a chance to put my dash and underhood filters and covers back together. For the first time in probably 15 years the A/C is working as it should. Nice and cold when I want it and heat when I need it.
    EricinConejo

    1995 850CI, 1959 Chev Impala, 1965 Cessna 172, 1986 Mustang GT, 2002 Mustang GT, 2005 Dodge Durango Hemi, 2016 Land Rover Discovery Sport

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