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C200 aircon fan problems

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by ventech, Feb 25, 2009.

  1. ventech

    ventech Member

    Likes Received:
    Jan 14, 2009
    My blower stooped working so I removed it and applied power directly to the terminals & it is OK. I assumed that the electronic module is faulty, but it could be the switch contacts on the rotary fan speed switch. I intended to replace the module £120 from dealer, but it could be the switch is faulty not the module.

    The heater/aircon blower is different in aircon equipped cars. There is an electronic module bolted to the casting that is not present on the non aircon blower. This is connected to a 4 pin plug. Two wires are heavy, probably 2.5 sq1 mm, and the other two are very thin. The rotary switch has 5 posn, so presumably it has resistor or some elements on it to produce a variable voltage to the electronics module. I have tried measuring the resistance between the two thin wires two each other & to ground in each position & found no difference in any position. This suggests that the contacts are open circuit.

    Can anyone expand on this & suggest further tests? It should be possible to test the module in situ by connected the control pins to a pot connected betyween +12V & ground.
  2. television

    television Always remembered RIP

    Likes Received:
    Mar 14, 2005
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    On the rear of the control unit, pin 7( that is if pin 12 is ground) should have a voltage of between 0 to 5.6 volt, this voltage goes to pin 2 of the fan regulator pack.

    Do not forget that there is a fuse for the fan motor in F1 that gives 12 volts to pin 3 of the regulator.

    The control units hardly ever break down, the switches and dials and press buttons all clean well with a good switch cleaner.

    Do check the length of the carbon brushes, as just by moving it could let it start, and this may be the only problem

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