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Thread: How does an E30 heater valve work?

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    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    How does an E30 heater valve work?

    E34 owner here, on a slow quest to reengineer the climate control system to be less complicated. The blower motor is a simple analog affair, and the air distribution system is all cable-operated (apart from recirculation), just like an E30's, so no problem there. Problem is heater valve control - valves normally held open by springs, closing by pulse-width modulation, controlled by a black-box module that isn't getting any younger and sooner or later is going to be NLA. I'm good with analog electrics but clueless about digital electronics, so I'm wondering about replacing the heater valve with something simpler. Perhaps an E30's? How does it work? Is there a cable or something from the heater dial, straight to the valve? Or is it also PWM? Something else?
    Last edited by moroza; 10-24-2017 at 01:43 AM.

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    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    The heater valve is a normally open water valve. Apply 12V to it and it closes. Really simple.
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    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    So how do you get something between full hot and full cold? Simple potentiometer, or PWM?

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    Since valve can only be either on or off, what you need to do is turn it on for a certain period of time and then turn it off for a certain period of time. The higher the temp setting the longer the on period is. At full hot the valve is always on. At full cold the valve is always off.

    After 30 years the temp controller in my e28 is still working just fine. When it craps out and my multiple spares crap out and I'm still kicking then I'm doing a cable operated VW valve.
    demet

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    Moroza- I am pretty sure the flap inside the heater / ac box somewhat effects the temp mixture between full hot and full cold. I recently replaced the whole box with fan and cores and all and noticed that outside air goes through the fan and then always runs through the ac core ...and there is big flap door that routes the air after it runs through the ac core to the area where the heater core is . there are four Bowden cables that control the flap doors for the air directions through the vents and the temp control selector not only controls one of the Bowden cables and also two stepper motors with rods going on left and right side that also control the flaps for air circulation .
    Last edited by 84318i; 10-26-2017 at 11:40 PM.

  6. #6
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    Found this answer. It's a potentiometer in normal E30 systems (there was apparently a rare optional E34-style automatic heater as well, though like the E34 it does not affect AC).

    Cables would be even better but the routing might be a giant headache.

    Also discovered that Benz W123 manual heaters had dual-zone cables. It doesn't get more elegant than this:


    - - - Updated - - -

    Quote Originally Posted by demetk View Post
    Since valve can only be either on or off, what you need to do is turn it on for a certain period of time and then turn it off for a certain period of time. The higher the temp setting the longer the on period is. At full hot the valve is always on. At full cold the valve is always off.
    E34, yes; the PWM signals from the IHKR module do this on-off 12V or 0V that you describe. On the E30, according to that PDF I found, no; a potentiometer (the temperature knob) directly varies the voltage to the valve, regulating how far it's open. It remains to be seen whether E34 heater valves will work that way.
    Last edited by moroza; 10-27-2017 at 12:51 AM.

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    Wow that great!

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