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Thread: Start cap

  1. #1
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    Start cap

    Could some of you guys provide me with some reason or your findings of why a hermetic compressor using a pump down and cap tube (actually it's more of a orifice) would have their start caps go within a month? This unit has had all its components replaced probably 3 times since January and now today I'm back for just the start cap this time. Where should I look. I can provide some data if needed but I'm looking for clues or ideas on something I may have missed.

  2. #2
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    Low voltage on start up at the compressor terminals is perhaps the most common cause. Another common cause can be short cycling at the beginning of a cycle on a low pressure switch [since you have a pump down] due to improper refrigerant management.
    A skilled Tech would solder a relay on that board and call it good to go.

  3. #3
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    I did take note that on pump down, low pressure opened at 10 which is good because I have seen techs run them down to 0 then as I watched lp side it seemed to rise somewhat fast but couldn't see anything happening to high side then at about 18 to 20 lp switch closed and pump down run again to 10. This time didn't see a fast rise on lp side. I figured risidue in accumulator boiling caused rise. Either way thought maybe this short cycle may be culprit and may recommend a one time pump down be wired. Also only a 8 to 10 ci to Co on low pressure switch seemed odd as well? Your thoughts please.

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    One more thing is using a pump down with a cap tube (orifice) system. Don't understand the benefits of this because pressure equalize readily on off cycle so when compressor is energized it's not under load.

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  6. #5
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    If the pressures are equalizing readily in the off cycle, that could be an important clue to your problem.


    Quote Originally Posted by farm tech View Post
    One more thing is using a pump down with a cap tube (orifice) system. Don't understand the benefits of this because pressure equalize readily on off cycle so when compressor is energized it's not under load.
    A skilled Tech would solder a relay on that board and call it good to go.

  7. #6
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    That last post of mine is miss leading. I'll think of a better way to explain after bit I have a couple of things to attend to.

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    Now I'll explain better. Cap sys. Unlike txv their pressure equalize quickly so the comp is not starting under a load therefore they don't need Start caps. A benefit of pump down would be for sys to not start under load and liquid migration during off cycle, correct? I've only been at this for almost 3 years but seems to me system I'm working with for one doesn't need start cap. Number two being system is cap tube a pump down really wouldn't be necessary unless someone was afraid of migration or there was a leak and pump down was an after thought because tech couldn't find leak and placed pump down on to try and control amount of freon loss. This solenoid isn't factory installed. Well that's the best I can do, hated to write a book. I have about half mind to either remove pump down or wire in a set auxiliary contacts and make a one time pump down.

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    What are you using for a relay current or potential

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    Potential

  11. #10
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    There's too much information that we don't know.

    But, done properly, a start cap will extend the life of a compressor.


    Quote Originally Posted by farm tech View Post
    Now I'll explain better. Cap sys. Unlike txv their pressure equalize quickly so the comp is not starting under a load therefore they don't need Start caps. A benefit of pump down would be for sys to not start under load and liquid migration during off cycle, correct? I've only been at this for almost 3 years but seems to me system I'm working with for one doesn't need start cap. Number two being system is cap tube a pump down really wouldn't be necessary unless someone was afraid of migration or there was a leak and pump down was an after thought because tech couldn't find leak and placed pump down on to try and control amount of freon loss. This solenoid isn't factory installed. Well that's the best I can do, hated to write a book. I have about half mind to either remove pump down or wire in a set auxiliary contacts and make a one time pump down.
    A skilled Tech would solder a relay on that board and call it good to go.

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  13. #11
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    Ask and I'll provide best I can from memory. This job is history now. Was wanting some clues if I need to go back or run into this again elsewhere.

  14. #12
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    Start cap

    Most pump down systems are primarily for off cycle oil and refrigerant migration management.

    What is the application?


    Sent from my iPhone using Tapatalk

  15. #13
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    As Heatingman alluded to, we don't have a clue about anything you are working on. And the information that was given was sketchy at best. I think you said it was a cap tube, then you said orifice (?).

    Then I think it came out you have a potential relay. So, another reason start caps blow is if the pot relay points stick. You see, we know virtually nothing about what type of equipment this is. Or how it was modified from the OEM.

    In the meantime, you may want to consider applying for pro membership status. Especially because we are very limited on what we are allowed to discuss about electricity on these open forums.


    Quote Originally Posted by farm tech View Post
    Ask and I'll provide best I can from memory. This job is history now. Was wanting some clues if I need to go back or run into this again elsewhere.
    A skilled Tech would solder a relay on that board and call it good to go.

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