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Thread: Rheostat and hard start kits.

  1. #1
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    Rheostat and hard start kits.

    Hello!

    I'm new to the site and hope I got the right location to ask a question.I've read many positive articles about "hard start kits" for A/C compressors . I'm not versed in electric theory of what happens during compressor start-up, but may I ask if the start kit operates similar to a DC motor rheostat?

    I remember having to start large DC motors in industry using multiple hand activated levers that had to be pushed down and clicked in place before going to the next lever.There were 4-5 levers and when the first lever is depressed,the motor starts to turn very slowly and as each lever is depressed (at the control box) the motor increases speed.It is done gradually and slowly .So, I likened it to a hard start kit.Am I right? Or out of touch!!
    Thanks

  2. #2
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    Jun 2013
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    No, an ac "hard start kit" is a correctly sized start capacitor paralled across the compressor's run capacitor via a nc relay.

    This relay is opened when a specific v is built up in the compressor.

  3. #3
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    Jan 2021
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    These are spiff items at my company. I never installed one yet because I'm still figuring out when it would be practical to put one in. I was thinking of just sending it on any outdoor unit over five years old but what would be some good indicators that the compressor could use one?

  4. #4
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    Quote Originally Posted by JehanDM View Post
    These are spiff items at my company. I never installed one yet because I'm still figuring out when it would be practical to put one in. I was thinking of just sending it on any outdoor unit over five years old but what would be some good indicators that the compressor could use one?
    Generally speaking you'd install one on a compressor that doesn't want to start easily.
    I've only installed a few, but those were on unit's that would trip the breaker when trying to start. Or they would start slow with an ungodly groaning noise for a few seconds.
    All it really is is adding a start capacitor and relay.
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

  5. #5
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    Quote Originally Posted by JehanDM View Post
    These are spiff items at my company. I never installed one yet because I'm still figuring out when it would be practical to put one in. I was thinking of just sending it on any outdoor unit over five years old but what would be some good indicators that the compressor could use one?
    Its been awhile since I've dealt with single phase power, but when I was doing residential, the only times I ever found a hard start kit to be truly necessary was due to a particular mix of equipment that I used to run into a lot, albeit about 10 years ago. I never suggested one "just because."

    When replacing Carrier cased evap coils, if they were keeping the old condenser. This was the old units, the ACA coils with the piston, on the the 38CK condensers that had recip compressors. When we changed the coils to the ATAs or ALAs, those have hard shut-off TXVs, and often, those compressors didnt like that, so they got a HS kit as well.

    I would assume that this particular problem is not much of a thing anymore. Rest of the times were just a handful of times where you give the customer that line about how the compressor was locked up and you ran it backwards and it's now working but they really should replace it, but I suggest this hard start kit in the meantime while you plan for a new unit and you never hear from them again.


  6. #6
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    Jan 2021
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    Another dumbass question? How do you run a compressor backwards? They turned me into an IAQ / turnover guy because I can sell, but it seems like I'm going to have to fend for myself on the technical side. The ones we use don't need a relay we just hook it up to the capacitor on the herm terminal.

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