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  1. #1
    Join Date
    Sep 2002
    Posts
    12,715

    A 3-wire fan / defrost termination switch?

    Red wire, brown wire, black wire.

    On a 120 volt system one wire has to be a common connection, one wire has to be the common to the X terminal on the defrost timer, and the other wire has to control the common to the evap fans.

    Which wire is which?

    Common?

    Close on rise?

    Close on fall?

    PHM
    ------
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  2. #2
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,795
    red is common
    black goes to the fan motor(red to black closes when evap gets cold)
    brown goes to X on timer(red to brown closes when evap gets warm).
    If wired that way..

  3. #3
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
    Posts
    861
    Is it a Klixon 4391? If so, the center terminal should be the common, I would think.

  4. #4
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,428
    If it's a three-wire Klixon Brand style (with two leads together on one side and the third lead opposite), ohm out the leads at room temperature. The two with continuity will tell you that one is common and the other terminator.

    The secret to which-is-which is that the fan lead and the terminator are alway opposite each other, so with this you can determine how to connect the t'stat even if all three wires are the same color (like with the cheap Mars Klixons I get at the supply house)

    As for the ones with all three leads on the same side, I think man form trane is correct that the center lead is alway common. So again, at room temperature, the two that have continuity are the common and termination. If the common is in the middle, then the open lead is fan.

  5. #5
    Join Date
    Sep 2002
    Posts
    12,715

    This is a cobbled Bev-Air

    It used to have seperate fan and termination switches. But now it has one of those three-wire universal switches.

    I got there and found no diagram on the unit, and no stat like that in the truck, the evap solid ice, and no common to the defrost heaters.

    Somebody 'fixed' it last week and now won't come back. So I get called and see what I think they did.

    It was late and I just stopped there on my way to some other crisis (I am always a sucker that way <g>) I just ran the heater common to a common terminal, defrosted the coil, set the time termination for about seven minutes, and told them I'd come back. Which may be today or tomorrow if things go smoothly and I can ever get out of the office! <g>

    Thanks!

    OH! It just occured to me: maybe the wrong switch is wired wrong AND is defective besides! <g>

    The right switches are a few days away; maybe I'll just wait for them. Although . . . . I'll feel better making the wrong thing work right. <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #6
    Join Date
    Mar 2003
    Posts
    190
    Is there a reason they can't include a wiring diagram of the switch in the package?

  7. #7
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    a light and a little bit of liquid refrigerant and you can easily determine the leads. LOL.

    I do this when I don't know which is which.

  8. #8
    Join Date
    Jul 2004
    Location
    NJ
    Posts
    1,795
    Quote Originally Posted by Dowadudda View Post
    a little bit of liquid refrigerant
    you mean diminicmus amount?

  9. #9
    Join Date
    Mar 2007
    Location
    wedged in freezer shelf
    Posts
    6,980
    Quote Originally Posted by wannafreeze View Post
    you mean diminicmus amount?
    He was saying uses liquid CO2

    Get your mind out of the gutter
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  10. #10
    Join Date
    Oct 2008
    Location
    florida
    Posts
    138
    interlink 3 wire defrost termination switch with black and blue wires in one side of switch and red out other side of switch.Blue and black closed warm room temp.
    Blue and red closed cold .part #b12 835 I would wire it blue to "N" red to fan common and black to X on defrost timer.And yes the red and black wires are directly across from each other as



    Icemister pointed out,{never noticed that Ice thanks for the info}
    Last edited by pelican; 10-05-2008 at 08:44 PM.

  11. #11
    Join Date
    Oct 2008
    Location
    florida
    Posts
    138
    mike if it was a small reach in with a 4 wire (little black timer}you had a heater limit switch not a 3 wire switch.it opens and turns off element when warm.then timer times out and starts unit.there will be no connection to timer,fyi.the details no matter how small would be helpful.my last post assumed you were on a walk in and were replacing a 3 wire switch.use blue and black tape off red.

  12. #12
    Join Date
    Sep 2002
    Posts
    12,715

    This is what happened and I think happened -

    Some one came to fix it. It originally had a four-wire setup: one close-on-fall 'klixon' for the evap fans and one close-on-rise 'klixon' for the defrost termination.

    They replaced those two with a single three-wire. The problem was that the original defrost switch closed common to the X terminal. Whereas the original fan switch closed power to the fan motors. That screwed them up.

    I couldn't alter the timer solenoid power so I wired the fans one-side-hot and broke the common to the fans through the three-wire.

    And now all is well. <g>

    Thanks!

    PHM
    -------



    Quote Originally Posted by pelican aire View Post
    mike if it was a small reach in with a 4 wire (little black timer}you had a heater limit switch not a 3 wire switch.it opens and turns off element when warm.then timer times out and starts unit.there will be no connection to timer, fyi. the details no matter how small would be helpful. my last post assumed you were on a walk in and were replacing a 3 wire switch.see what happens when u ass u me?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  13. #13
    Join Date
    Mar 2007
    Location
    wedged in freezer shelf
    Posts
    6,980
    PHM You gonna fire up the grill on the 31 st. this year again?
    “If You Can Dodge A Wrench You Can Dodge A Ball”

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