Fan control will not work. Knob turns but fan wont come on.

Discussion in 'General Motoring' started by bwc, Nov 10, 2008.

  1. bwc

    bwc Guest

    Does anyone know what the problem/solution could be?
    I have a ’97 civic sedan. When I turn the fan knob on nothing
    happens. The fan isnt coming on, no heat or AC will come out.
    I checked the fuses and none are blown. I pulled the knob off and the
    actual metal piece turns fine...
    this just happend the other day for no apparent reason.
    any ideas??

    bwc, Nov 10, 2008
  2. bwc

    W????n S. Guest

    On my honda it was the motor itself. Interesting to fix but not hard per
    se. 88 honda accord lxi.
    W????n S., Nov 10, 2008
  3. bwc

    James Sweet Guest

    I assume this applies to all speeds? Many cars use a resistor to drop
    the motor voltage for the lower speed settings, then bypass it for the
    high speed. If the resistor burns out you get high speed or nothing. If
    that doesn't work either, the next step is to check for voltage at the
    power terminal on the motor, some cars this is easy, others it's as if
    they put the blower motor on a pedestal and built the car around it.
    Also you mention you checked the fuses, but you may want to try
    replacing the blower fuse anyway, or at least make sure that other
    accessories, if any, on the same circuit work. It's rare, but I've seen
    mechanical failures in fuses where the element cracked off at one end,
    still appearing intact but not completing the circuit.
    James Sweet, Nov 11, 2008
  4. bwc

    bwc Guest

    Thanks for the help guys!

    Well mechanic says its the Heater Blower Control Motor, and its close
    to 400 for the unit (or whatever it is).

    Anyone know anything about that, and if I could easily do it myself or
    if I could find it cheaper? Why would it just die for no apparent

    Thanks agai
    bwc, Nov 12, 2008
  5. bwc

    bwc Guest

    oops the car is a 2003 not 97 (if it matters)
    and the part as per mechanic is called "heater control head
    bwc, Nov 12, 2008
  6. bwc

    James Sweet Guest

    Sounds like it uses an electronic controller for the fan motor instead
    of a simple resistor and switch. If you can open it up, there's probably
    a power FET driving the motor, these tend to fail shorted though so I
    would first look for hairline cracks in the solder joints under the
    circuit board around this and the pins on the connector where the wiring
    harness plugs in. Assuming you lack the skills to diagnose and repair
    this, you could try and find someone who does, or keep an eye on ebay or
    call some salvage yards. Could look online for parts suppliers but this
    sort of thing is often a dealer-only part.

    As for why it would die, this sort of thing happens all the time. One
    major challenge in mass producing printed circuit boards is soldering
    when you have a mixture of components with large heavy leads and small
    light stuff. It's tricky to wave solder it such that you get sufficient
    solder on the heavy stuff without burning up the small parts. On top of
    this you have vibration and mechanical shock which can lead to
    fractures, and temperature swings causing fatigue from expansion and
    contraction, a car being a particularly harsh environment in both
    respects. Components can fail as well, but I have seen surprisingly
    little of this in automotive electronics. Shorted capacitor in the ECU
    was the fault preventing a friend's VW Scirocco from starting, seen a
    few bad ones that would cause dashboard clocks and speedometers to
    function erratically or not at all in cold weather, but overall not very
    many. Sometimes the design and construction are quite adequate and
    things just fail, luck of the draw, it happens.

    If the thing is already dead, there's no harm in popping it open to have
    a look, so long as you know you're popping open the correct part.
    James Sweet, Nov 12, 2008
  7. lists a bunch in my state, including a couple at my local
    wrecking yard, ranging from $50 to $110. Give it a try!

    Michael Pardee, Nov 12, 2008
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