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Air conditioner contactor snubber.

Discussion in 'Electronic Basics' started by GEORGE S JAYNES, Aug 1, 2005.

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  1. My contactor has just killed two thermostats in a row. Yes, i will get a
    new contactor. Anybody know what values to use on this 24vac coil?
     
  2. Guest

    What makes you think it is the contactor....couldnt it be some kind of
    intermittent short....or some other problem.

    I work on air conditioning systems on a daily basis and rarely find bad
    thermostats...especially bad thermostats caused by contactor
    coils........

    what makes you think the contactor is at fault...did you recently
    install both these thermostats only to have the contactor destroy them
    ???
     
  3. I don't think most thermostats are capable of driving a motor
    contactor, directly. You need a small relay between them. 24 volt AC
    coil and something like 5 or 10 amp contacts. Something with a less
    than 1 watt coil. This might work:
    KUP-11A15-24 at the bottom of
    http://dkc3.digikey.com/PDF/T052/1290.pdf
    This can be socketed, or connected with separate wires with push on
    crimp terminals.

    Then get a contactor with a generous contact rating, compared to the
    current your compressor takes. It can have a 120 or 240 VAC coil.

    A 47 ohm in series with .47 uF across the thermostat contact will
    reduce the turn off flash.
     
  4. Guest

    a contactor is nothing more than a large heavier duty relay...On most
    residential systems and commercial hvac systems you will have 24 volt
    coil contactors controlling the compressors.

    Go take the door off any residential or light commerical heat pump or
    straight ac and you will find the compressor contactors using 24 volt
    coils
     
  5. Both thermostats were electronic. the first was in use five years, the
    second lasted less than a month. that's why i am thinking contactor needs a
    snubber.
     
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