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  1. #1
    Join Date
    Jul 2019
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    heat-pump-defrost-issues

    Hi,

    Had a new lennox xp14 heat pump installed and have a few issues since new (installed 2018):
    1. even in warmer weather (ambient temperatures from 65 -70F), the system kicks into defrost mode. WTH? That can't be normal. Defrost board fault identified and replaced several months ago when system was defrosting at 55F. Now defrosts as well around 70F
    2. again in warmer weather, outdoor compressor drips a lot of condensation (even at 60-65 degrees) - maybe that's normal for some newer units, but seems excessive.
    3. colder weather, defrost mode is associated with a disturbingly loud elephant-like trumpeting noise. Mixing valve? But still, this level of noise cannot be normal.

    Any guidance is welcome.
    Thanks!
    Greg

  2. #2
    Join Date
    Aug 2002
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    Southold, NY
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    Why are you running it in heat mode at 70F?

  3. #3
    Join Date
    Jan 2012
    Location
    Missouri, USA
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    The defrost sensor should have replaced with the board. Sounds like you might not have needed a new board.

  4. #4
    Join Date
    Sep 2007
    Location
    edmonds wa
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    Some boards do a defrost on accumulated time even though the defrost sw has not initiated it. Kinda of a fail safe defrost.
    UA Local 32 retired as of Jan 2020

  5. #5
    Join Date
    Jul 2007
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    Virginia
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    Quote Originally Posted by grege View Post
    Any guidance is welcome.
    Thanks!
    Have the installation company verify the refrigerant charge, and the functionality of the two sensors that control the defrost cycle.

    Should one of these sensors fail, the unit will defrost every 34 mins of compressor run time when the coil reaches the specified temp.

    This units should shut the compressor down for 30 seconds during the switch to defrost, and then back to heating. This is what eliminates the "Moose Call" noise you are hearing. Have you tech verify that too.
    Instead of learning the tricks of the trade, learn the trade.

  6. #6
    Join Date
    Jul 2019
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Why are you running it in heat mode at 70F?
    House is shaded with thermostat set to 68F (63F at night), so the interior house stays cooler than ambient until the afternoon when the system kicks in and starts defrosting.

    Greg

  7. #7
    Join Date
    Jul 2010
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    nebraska
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    The demand defrost board will go into defrost every 6 hours,even in mild weather, for oil return. Could be sensor problems or running as designed depending on how often it shifts over.
    Moose call shifts are usually hot gas too hot and softens plastic in reversing valve. Tech needs to check refrigerant charge and temperature of compressor discharge line.

  8. #8
    Join Date
    Jul 2019
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    Thread Starter
    Quote Originally Posted by martyinlincoln View Post
    The demand defrost board will go into defrost every 6 hours,even in mild weather, for oil return. Could be sensor problems or running as designed depending on how often it shifts over.
    Moose call shifts are usually hot gas too hot and softens plastic in reversing valve. Tech needs to check refrigerant charge and temperature of compressor discharge line.
    Oddly, when I first encountered this ealier this year, defrost was kicking in above 50F. My HVAC company's supervisor said it was normal as it related to programmed defrost cycles. An experienced technician I mentioned this to said, no, it isn't normal and only then found a defrost board fault. Since that was replaced, I just recently found the defrost cycle kick in above 65F which makes me think if 50-55F defrost was abnornal, then 65-70F is also abnormal. Refrigerant charge was reportedly normal, so...??? IDK. This, plus the moose calling leaves me completely unimpressed by lennox thus far.

    Greg

  9. #9
    Join Date
    Jul 2019
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    Thread Starter
    Technician checked it out and all pressures and specs are "normal". Replaced a pitted capacitor (just under 2 years old).

    Other: Because the system would cycle on and off too much with the factory 1F temperature differential, I changed it to a 1.5F degree differential and when the house T-stat is set to 68F, auxiliary heat will kick in when the t-stat reads 67F, which suprises me because it will do this even when it's 40F outside.

    Whole system uses an icomfort wifi lennox thermostat with lennox's CBX32-MV signature air handler. Not impressed with lennox if this system is "working per spec". It's been louder, less efficient, and far less reliable than the trane xl13i it replaced.

    Greg

  10. #10
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    Time/temperature defrost control is furnished as
    standard equipment.
    Control initiates a defrost cycle every 30, 60 or 90
    minutes of compressor “on” time at outdoor coil
    temperatures below 42F. Factory setting is 90 minutes.
    Anti-short cycle, timed-off control (5 minutes).
    Compressor delay (30 seconds, field selectable) for
    cycling the compressor in and out of the defrost mode.
    High and low pressure switch monitoring with five-trip
    lockout.
    Two diagnostic LEDs furnished as an aid in
    troubleshooting.
    Conveniently located in control box.
    Anti-short cycle (5 minutes) incorporated into the board.
    Diagnostic LEDs furnished as an aid in troubleshooting.

    Only thing I see is the temp at which the defrost stat closes is 42 which seems high compared to most. But even if it is running in heat at 60 ambient, the outdoor coil shouldn't hit 42. Need to be sure it is on 90 minutes but still if the defrost stat is not stuck closed, shouldn't be defrosting.

  11. #11
    Join Date
    Aug 2002
    Location
    Southold, NY
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    GH
    Quote Originally Posted by grege View Post
    Technician checked it out and all pressures and specs are "normal". Replaced a pitted capacitor (just under 2 years old).

    Other: Because the system would cycle on and off too much with the factory 1F temperature differential, I changed it to a 1.5F degree differential and when the house T-stat is set to 68F, auxiliary heat will kick in when the t-stat reads 67F, which suprises me because it will do this even when it's 40F outside.

    Whole system uses an icomfort wifi lennox thermostat with lennox's CBX32-MV signature air handler. Not impressed with lennox if this system is "working per spec". It's been louder, less efficient, and far less reliable than the trane xl13i it replaced.

    Greg
    I love “Normal” pressure readings.............some day I may see them!

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  13. #12
    Join Date
    Jan 2004
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    PA
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    Quote Originally Posted by martyinlincoln View Post
    The demand defrost board will go into defrost every 6 hours,even in mild weather, for oil return. Could be sensor problems or running as designed depending on how often it shifts over.
    Moose call shifts are usually hot gas too hot and softens plastic in reversing valve. Tech needs to check refrigerant charge and temperature of compressor discharge line.
    Not at outdoor Temps above 55F.
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    How many times must one fix something before it is fixed?

  14. #13
    Join Date
    Jul 2019
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    Thread Starter
    Between 55 and 60F today and sure enough, defrost kicked in again while I was home after work. A few minutes ago, I grabbed a temperature probe to measure the Y trunk interior duct temperature (just above and within one foot of the main blower cabinet-wyed trunk intersection) as well as the return duct next to the blower unit. The wye trunk supply heat measured 89F while the return measured 69F (holding the probe within each trunk for two minutes after the system was running for a few minutes already). House thermostat is set to 67/68F.

    55F outside: isn't 89/90F supply temp that close to the blower pretty weak/low?

    Thanks,
    Greg

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