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Thread: Contactor wont pull it

  1. #21
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    This is a trane, is the output of the board a snubber circuit?

  2. #22
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    It will have a snubber.
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    2 Tim 3:16-17

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  3. #23
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    Thread Starter
    Does the snubber prevent arcing in the low voltage relay? Not overly familiar

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  4. #24
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    Quote Originally Posted by Spitz View Post
    Does the snubber prevent arcing in the low voltage relay? Not overly familiar

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    Yes.

    If you think back to the Kettering (breaker point) ignition systems, the capacitor (called a "condenser" in old radio lingo) was used to extend the life of the point contacts by reducing arcing during the hundreds of thousands of operations, until the points were replaced at the next "tune up."

    One key point when working with the Trane snubber circuit is the fact that a high impedance multimeter will allow you to measure a voltage at the circuit outputs when no load (contactor) is connected to the leads because of the ability of the snubber to pass a trickle of current even when the outputs are de-energized, which is more than enough to power a meter with an 11 meg input impedance.

    A connected load like a contactor shunts that trickle current, so you will read zero volts across the de-energized coil terminals.
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    2 Tim 3:16-17

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  5. #25
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    Sounds like a safety to me or some sort of loose/intermittent connection.

    Can you clip an alligator clip to the wires and run them to your meter and see what the voltage is as it's happening? Could be a voltage drop just big enough to cause it to drop.

    When does it happen? As soon as the comp starts or after a couple of minutes and pressure builds up?

  6. #26
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    Thread Starter
    Talked to Trane tech support told me to run my 24v thru a relay which I had already done. He said the UPC may be at fault and has had this same call multiple times in the last few weeks. When I installed the relay I fed the N.O. contacts with it's own 50VA transformer, apparently a 50VA is not big enough to pull in the contactor. I put the 24v side directly to the coil and it would not pull in. Yes the OEM transformers are 75VA but they feed multiple contactors along with the damper actuators. I did wire the same transformer and contactor to 120v at my home and it pulled in no problem. I left the relay in place and ran a wire off the secondary to the relay contacts. The relay coil is energized by the original coil wires. If I get a call back they will be getting a contactor with a 208v coil and a new board.

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  7. #27
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    Quote Originally Posted by Cool breeze 38 View Post
    that is a 50va transformer? sounds like its not big enough. going by your spec sheet it needs 32 va to hold it, which is the 1.1 amps. but needs much much more to pull it in. what was the original transformer size.

    you could put a rib relay and a 208 v coil. it would fix it. take the current contactor coil leads and put them to the rib coils. then 208v coil on the contactor
    You win

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  8. #28
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    which way did you solve it, transformer or relay and a 208 coil

  9. #29
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    Thread Starter
    Got rid of the 50va transformer I installed. Took the original coil wires that came from the control board and put them on the coil wires of a rib relay.(A RIB relay will pull in at 10 to 30 VAC/VDC). ran 24v from the original 75VA transformer to N.O. contacts of the rib relay.

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