Heater Control module

Discussion in 'Audio + Electronics' started by Squirel, Aug 9, 2018.

  1. Squirel

    Squirel Newbie

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    I have had my '91 since December nad have just gone through my 3rd heater control module. The second one actually quit and then started working for a while. Asny idea's on a cause and more importantly a fix.
     
  2. Blue Turd

    Blue Turd I'm Awesome

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    What exactly stops working in the module? Usually it’s the fan speed people lose, as the blower motor has inadequate wiring and burns out either it’s own connections, or worst case, the HVAC controller itself.

    Remove the glove box and trace the blower motor wires to its plug. If the wires aren’t already burnt looking, the plug probably is on the inside.

    I added a bigger high amperage plug (the kind used with hobby RC batteries), and added an inline fuse between the motor and it’s power source. This way if it were to go wacky, it would blow that and not anything expensive or difficult to replace down the line.
     
  3. Squirel

    Squirel Newbie

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    The whole display goes blank.
     
  4. Blue Turd

    Blue Turd I'm Awesome

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    Display? All I have are knobs. I didn’t know they even offered auto climate control, especially in 91.
     
  5. df2x4

    df2x4 Domestics only.

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    '91-'94 (I think) got these units. I always thought they were kind of cool. No actual temperature settings in degrees or anything fancy, just digital controls and display.

    [​IMG]
     
  6. Blue Turd

    Blue Turd I'm Awesome

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    Okay cool, I have some older cars with non auto units like that. I have a 95, so excuse my ignorance.

    I think the blower motor problems still exist, regardless of what type of control unit you have. What I don’t know however, is if that problem is present, how it affects the older style control units.

    When you replace the unit, did you ever notice any burnt or otherwise damaged wires or connection points?
     
  7. Squirel

    Squirel Newbie

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    Every thing looked normal. Would a problem with the blower motor affect the rest of the module, as in the whole control dieing and going blank?
     
  8. Squirel

    Squirel Newbie

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    That's exactly what mine looks like, or should say, is supposed to look like, mine is completely dead, no display what-so-ever.
     
  9. Blue Turd

    Blue Turd I'm Awesome

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    Possibly? But I don’t have that type of module in my truck so I have no personal experience with it.

    I’d still check behind the glove box and the blower motor connections to rule it out. It’s an easy job.

    Beyond that, that’s the only issue I know that affects the control unit. The servos that change air direction and temperature also fail, but aren’t known to cause issues with the control unit.

    It might just be a crappy ground somewhere, as these truck are notorious for those. That might explain why you said it sometimes comes back after dying.

    There should be some fellows on this site who might have the wiring diagrams and ground locations for the 91 HVAC system.
     
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  10. lxe4

    lxe4 Newbie

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    i dont have that unit in my 96 but the blower motor got tight and started drawing to much on the lower settings and burning up the speed switch. i had time a few spare shit fan motors and no money so i got into rebuilding the motor. its a prick to get apart and back together but after polishing the shaft and bushings and reipregnating the oilite bushings and the felt washers around them, the motor is quiter than ever. a new motor would have done it too. its not easy to relube the fan side bushing without taking it all apart.
     

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