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  1. #1
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    Compressor thru R-valve, short cycle question

    I've always diagnosed a mid-way stuck r-valve by following the heat of the compressor discharge through the r-valve and back to compressor suction. The discharge gas has no problem getting hot and hotter as it is short cycled.

    But yesterday I observed the same thing but the discharge took a while to get a little warm and never got really hot like I would expect.
    This was a Copeland scroll ZRK5. Can anyone explain why?
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  2. #2
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    Just a couple of WAGs. Maybe the compressor is bad too. An Rv stuck blowing back into the suction line long enough can damage the compressor. The amount of gas in the system could also be a factor.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  3. #3
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    Compressor is what I was thinking as well but can hardly believe it. I'm going to change r-valve tomorrow since I have little doubt about its failure. I'll know for sure then and update this post.

    I wonder if copeland has some built in mechanism that "unloads" if high pressure enters the suction? Possibly by separating the scroll plates?
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  4. #4
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    Quote Originally Posted by penderway View Post
    I wonder if copeland has some built in mechanism that "unloads" if high pressure enters the suction? Possibly by separating the scroll plates?
    They do, it makes a psssssshhhh noise.

  5. #5
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    Quote Originally Posted by ryan1088 View Post
    They do, it makes a psssssshhhh noise.
    LOL, yes I'm familiar, thanks for the laugh.
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  6. #6
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    May 2011
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    Western, KY
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    Could it also be grossly undercharged?

    I know under normal circumstances if you remove charge the discharge temp goes up and vice versa but I've noticed in gross overcharge situations the pressure has risen so much the discharge temp is also very high. So in gross undercharge situations could there only be so much heat gain before the discharge temp stays lower than normal?

  7. #7
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    Quote Originally Posted by mason View Post
    Could it also be grossly undercharged?

    I know under normal circumstances if you remove charge the discharge temp goes up and vice versa but I've noticed in gross overcharge situations the pressure has risen so much the discharge temp is also very high. So in gross undercharge situations could there only be so much heat gain before the discharge temp stays lower than normal?
    I don't know about that yet. The standing pressure indicated that there was liquid refrigerant present.

    I'm just baffled at how refrigerant can be compressed out the discharge and then short cycled back into the suction without getting hot quickly. Maybe the compressor really is bad and cannot pump very well. I'll find out tomorrow after replacing r-valve.
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  8. #8
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    Aug 2001
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    Replaced R-valve today. Opened it up and observed slight melting of the teflon inard. It was overheated during its install by a green tech with a lot of potential. It was his first r-valve install.

    Compressor pumped just great with new r-valve. I'm guessing that copland has built in an unloading feature that activates if high pressure discharge gas enters the suction inlet.

    Has anyone heard of this? does anyone have a number for copeland tech support? or emerson maybe. I just hate not understanding
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  9. #9
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    Quote Originally Posted by penderway View Post
    Replaced R-valve today. Opened it up and observed slight melting of the teflon inard. It was overheated during its install by a green tech with a lot of potential. It was his first r-valve install.

    Compressor pumped just great with new r-valve. I'm guessing that copland has built in an unloading feature that activates if high pressure discharge gas enters the suction inlet.

    Has anyone heard of this? does anyone have a number for copeland tech support? or emerson maybe. I just hate not understanding
    Well the same psshht noise happens on high head pressure from dirty coil, overcharge, and dirty indoor coil in heat mode(read high head pressure).

    How is it activated? Temp or pressure? If temp then I'm sure a compressor that is looping has high temp from higher suction temps and heat of compression.

  10. #10
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    Quote Originally Posted by mason View Post
    Well the same psshht noise happens on high head pressure from dirty coil, overcharge, and dirty indoor coil in heat mode(read high head pressure).

    How is it activated? Temp or pressure? If temp then I'm sure a compressor that is looping has high temp from higher suction temps and heat of compression.
    There was never a pssssst!. I know the internal pressure relief activates on high internal discharge pressures. But that is not what happened or what I'm trying to describe.

    See from my OP that the discharge was slow to get warm pressure was low in discharge.
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  11. #11
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    One more bit of info I forgot to mention, tech had to remove discharge line from compressor to r-valve and drain the oil out. before he could put new r=valve in. He said it was very full. I'm also wondering why did that happened?
    "If perfection is your goal, you may end up with good enough, what might you end up with when good enough is your goal?"
    efficientcomfort.net

  12. #12
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    May 2011
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    Western, KY
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    I see, I was confused by your response to ryan.

    I haven't experienced the scenario you describe in which the discharge is only luke warm and oil logged. Keep us updated if you get more info.

  13. #13
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    Aug 2004
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    North Richland Hills, Texas
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    K5 scroll compressors for AC have temperature protection, similar to the ASTP on the newer refrigeration scroll compressors, but implemented a little differently(cheaply).

    If the discharge gets to hot, a bi-metal valve opens and directs most of the discharge gas down onto the shell of the compressor, where it will eventually cause the thermal overload to trip.

    The oil logging of the discharge line may be an indicator that it was cycling like that for a good while, as there will still be discharge gas, and oil, exiting the compressor into the discharge line, but not enough gas to carry the oil far.
    If more government is the answer, then it's a really stupid question.

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