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  1. #1
    Join Date
    Nov 2006
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    Athens, Ohio
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    Modulating heat pump does not defrost

    I checked an American Standard heat pump on Dec. 1. The owner had reported heavy frost that was not removed by defrosting cycle. Since the house was empty he had turned it off and it thawed from warmer temperatures.
    Everything I found was within specs. Here's what I recorded: 87/305 PSI @ 43* (R410-A, obviously). Subcooling was 21*, spec was over 10*. There's no access to the suction line to check superheat. The air filter is a 5" box filter and new.
    I checked resistance of all the sensors with the tables and they were accurate.
    The owner reports it has heavy frost again. The temperature has dropped and RH has been around 50% so we're have conditions for frost.
    What do you guys suggest I check next? These heat pumps are so new that I have no experience in troubleshooting them. I also have no experience with demand defrost, I'm used to timed defrost.
    I have asked Rundawg for a manual already so I can have some documentation.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


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  2. #2
    Join Date
    Oct 2002
    Location
    Plano, TX
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    I had a problem with a Trane a few years ago.

    You stated the house was empty. My customer kept the house cool and even colder at night. Trane determined that there was not enough sensible heat to provide adequate heat to defrost outside coil before termination.

  3. Likes BaldLoonie liked this post.
  4. #3
    Join Date
    Nov 2006
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    Athens, Ohio
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    Thread Starter
    Quote Originally Posted by timjimbob View Post
    I had a problem with a Trane a few years ago.

    You stated the house was empty. My customer kept the house cool and even colder at night. Trane determined that there was not enough sensible heat to provide adequate heat to defrost outside coil before termination.
    That's something that might apply here, too. Thanks.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  5. #4
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    10,282
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    Trane has suggested on every heat pump that they have ever produced that I know about is the return air temp being above 60 or there could be defrost issues. We have a bunch of snowbirds here that want to turn the temp down in the house when they leave for the winter and I always suggest they turn the system to EM heat and turn the temp down to 50.

    The problem is that the defrost controls will terminate defrost in 10-12 minutes which with cold return temps is not long enough at cold ODTs for complete defrosts. If the house is empty turn it to EM heat and drop the temp. It doesn't take much to keep the house warm so there is not a huge operating cost.

  6. #5
    Join Date
    Jul 2007
    Location
    Virginia
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    Quote Originally Posted by kdean1 View Post
    I have asked Rundawg for a manual already so I can have some documentation.
    I resent them to the other address you gave me. Let me know if you get them.
    Instead of learning the tricks of the trade, learn the trade.

  7. #6
    Join Date
    Nov 2006
    Location
    Athens, Ohio
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    Thread Starter
    Quote Originally Posted by rundawg View Post
    I resent them to the other address you gave me. Let me know if you get them.
    I received the manual. Thank you Randy.

    And thank you to all the others who have replied. I have never before encountered a house where they kept the indoor temperature so low. I suspect that is the problem. I'll post back after I resolve it.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  8. #7
    Join Date
    Jul 2006
    Location
    Prata di Pordenone
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    7,658
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    You might need to update the software on the drive
    call your Fsr
    Go Trump

  9. #8
    Join Date
    Sep 2015
    Location
    Ontari-ari-ari-o
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    Never encountered this before but it's something I'm going to file away for later. Funny what you can learn here just killing time.

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