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replacing a start capacitor

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  1. #1
    Apprentice (new member)
    Join Date
    Apr 2010

    Default replacing a start capacitor

    I have a ducted heating system which has a heat exchanger + industrial looking fan that draws the air through the exchanger and out through the ducts. It broke down a couple of years ago and I called someone out and they replaced the start capacitor and I think it has failed again. It sporadically started for a while and now will not come one at all. Similar to what happened originally

    I have opened up the unit and it is a 4uf +-5%, 450v cylindrical cap. It has 4 connectors on the top - with 2 red wires and 1 white going to it. I was looking for a replacement and have found the following that looks like the current one
    DUCATI||CAPACITOR, 4UF, 450VAC | Farnell Australia

    I was after some confirmation that it would be suitable - I am confused as the farnell one states that it has 2 pins, although the picture looks like 4 - and I have 3 wires going to the current one.

    Hope somebody can help or tell me what else I need to check to make sure I get the right one

    Thanks in advance for any assistance

  2. #2
    2K Club Member chrisp's Avatar
    Join Date
    May 2004
    Melbourne, Australia


    The capacitor from Farnell looks like the right type.

    While it is worthwhile replacing the capacitor, I wouldn't be over confident that replacing the capacitor will fix the problem. A motor can draw excessive current when the start capacitor fails and the motor remains stalled. Sometimes the motor burns out and sometimes the circuit breaker trips.

  3. #3
    Apprentice (new member)
    Join Date
    Apr 2010


    Hi crisp,
    Thanks for the confirmation - put a new one in yesterday and all now good. I love it when a $12 part and 5 minutes work saves a bundle!
    thanks again

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