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Thread: 88 735i heater issue

  1. #1
    Join Date
    Jul 2010
    Location
    Westlake,OH
    Posts
    112
    My Cars
    1988 BMW 735I

    88 735i heater issue

    My 88 735i has a heater problem: All the knobs are on the cooling mode, but heat is coming out of the vents regardless. I took the sword out where I have noticed that a MOSFET is charred, hence only the low and high speed for the blower ( I think this is the reason), but I suspect a heater valve being defective. Is there a procedure to test the heater valve?
    Thank you,

  2. #2
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    http://www.bimmerboard.com/forums/posts/841827/
    how to disassemble the heater valves is shown on my website below, maybe they are dirty and stuck.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
    Join Date
    Jul 2009
    Location
    Richmond, Virginia
    Posts
    1,683
    My Cars
    '88 735i, '06 RSX
    Could also be bad IHKA module. Replacing the heater valves with a new bosch unit did not fix my situation. Reflowing the solder joints on the IHKA unit helped fix the constant heat problem. Probably the better route is to get a rebuilt unit from ProGrama eventually....for every electronic bit on this car.

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