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  1. #1
    Join Date
    Dec 2011
    Location
    Cincinnati, OH
    Posts
    6

    Trane XL20i defrost when no ice present

    My 2 ton Trane XL20i heat pump was installed Aug 2010. All OK until temperatures got below 38 degF. At times the unit went into defrost with no ice on coil and times out at 15 minutes in defrost. The installer first replaced the defrost board and when that didn't work (in contact with Trane) finally replaced the entire outdoor unit and the indoor coil and expansion valve. By that time (March, warmer weather) the issue faded. Now (Dec 2011) it's starting all over again. Otherwise, the unit heats and cools fine. Any ideas?

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,586
    How often a day is it doing this.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,244
    If you have your tech back out, ask him to check the calibration of the sensors(if they are thermistors) and check that they are positioned correctly, I seems strange to time out on defrost, but at the same time its odd that 2 separate units are doing the same thing.

  4. #4
    Join Date
    Dec 2011
    Location
    Cincinnati, OH
    Posts
    6

    Trane XL20i defrost when no ice present

    Thanks, I'll call the installer (Trane certified) Monday.

  5. #5
    Join Date
    Dec 2011
    Location
    Cincinnati, OH
    Posts
    6
    This morning it's done it three times already. Interestingly, it stayed in defrost only 3 minutes the last time. When it gets repetitive, I throw the breaker on the compressor for 10 minutes to "reboot" its confused brain. Eventually, it decides to behave (usually when it gets warmer (35 degF now).

  6. #6
    Join Date
    Apr 2001
    Location
    Over Here
    Posts
    1,105
    Most defrosts initiate upon a temperature sensing device on one of the refrigerant lines inside your heat pump. It cannot determine if there is ice or not on the unit. When heat pumps operate below a certain ambient temperature, the line temperature is already below initiation threshold. Then the defrost board is looking for elapsed running time, and when that is met, it throws it into defrost.

    If there is ice on there, it will operate in defrost until the ice melts, and termination temperature is met. Sometimes that is a while - especially when you are watching it. If no ice, the termination temperature is met quickly, and the unit goes back into heat mode.

    The variable here is how much moisture content is in the air that condenses and then freezes on the outdoor coil. It sounds like your system is operating as it should.

  7. #7
    Join Date
    Dec 2011
    Location
    Cincinnati, OH
    Posts
    6

    Trane XL20i defrost when no ice present

    Last winter, the Trane factory tech watched my unit and agreed with me that three 15 defrosts in two hours with no ice on the coil is not proper operation of their demand defrost system. When it was defrosting for 15 minutes every half hour, COP was way less than 1. Right now at 36 degF I'm calculating COP of 3 and defrosting spasms have stopped for now. This is my third heat pump (second Trane) and have never seen this before.

  8. #8
    Join Date
    Dec 2011
    Location
    Cincinnati, OH
    Posts
    6
    Oops, I meant "three 15 MINUTE defrosts" on last post.

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