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  1. Trane Defrost Issues

    Hi there!

    I am the lucky owner of a Trane XR14 (2.5T) heat pump installed in June 2008. During the first winter, I called the installer because of weird defrosting behaviour: it was defrosting very often and for 10 minutes every time (it also had the timed defrost error code on the defrost board). So the installer came and said the defrosting control board was bad so he replaced it. I didn't pay too much attention to the unit afterwards but it seemed to defrost less frequently so I thought it was all good.

    One year later... Since a couple of weeks, it looks like the trane is defrosting very often (sometimes 2 defrost cycles in less than 1 hour), eventhough there is no frost on the outside coil. When the unit defrosts, everything looks normal: I hear the reversing valve (tsishhh), the compressor starts with the fan off and the unit outside gets hot. The defrosting cycle lasts between 5 and 8 minutes.

    So I called my installer and told him everything. In short, he's saying that he never heard of customer having unnecessary defrost cycles and don't really know what to do. To help him a little bit, I placed a temperature sensor on the freon line near my handler to see how often the HP is acting up. Here are the results for the last 12 hours. Dips around 10oC are defrost cycles. Spikes to 50oC are heat cycles. As you can see, it is almost defrosting after every heating cycle or so since this morning. The outside temp this morning is around 0oC. I went outside when I heard the reversing valve at around 11h20am this morning and there was no ice on the unit. Are these defrost cycles normal?? Any help would be really appreciated!

    Thanks!
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  2. BTW, I just tested the resistance for both sensors and they aren't too far from each other (27K for ambient vs 32K for coil). Something else caught my attention though: the defrost board I have installed is a CNT05004. Looking at the unit parts list though, the control defrost board should be a CNT02935 (which I think has been replaced by CNT04364). So here's my question for all the Trane's guru: Is it possible I don't have the right defrost board? My heat pump model is: 4TWR4030A1000A. Thanks again!

  3. #3
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    As far as I know all the residential heat pump boards work basically the same (there are minor differences) and you shouldnt have that many defrost cycles. They use a nice demand defrost. I have had several bad outdoor expansion valves on Various ages Trane Heat Pumps this year. If there is a problem with the refrigerant circuit it will defrost more often due to lower pressures causing lower temp at the coil sensor. My recommendation is find a reputable guy who you trust and ask him to compare your refrigerant pressures to the Trane ServiceFacts Charts. These are axcessible by the service tech.

    Have him test the thermistors thoroughly by heating them and them cooling them and watching them fluctuate

    just a hunch but maybe you have a freon leak

  4. Quote Originally Posted by amasuperbike View Post
    I have had several bad outdoor expansion valves on Various ages Trane Heat Pumps this year. If there is a problem with the refrigerant circuit it will defrost more often due to lower pressures causing lower temp at the coil sensor.
    Thanks for your input! I will call him again tomorrow morning. For the outdoor expansion valve, you detect a bad one by looking at the pressures? Is it easy to differentiate a bad expension valve from a improper refrigerant charge?

  5. #5
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    To be quite honest it can easily be overlooked. Your Trane unit should have all the pressure charts inside it so he can compare what the temp is outside and what the temp is inside the house and then it will give you a plot for what the pressures should be. As long as its in the ballpark of that chart than the valve and the freon level are ok.

  6. #6
    try moving the < No DIY instructions >
    Last edited by beenthere; 01-20-2010 at 09:56 PM. Reason: Removed DIY instructions

  7. Quote Originally Posted by kytech77 View Post
    try moving the defrost time to 60 minutes. I had one a couple of weeks ago that gave me fits. Also make sure the sensor is located correctly
    I don't think there is a jumper on this board as it is an on-demand defrost.

  8. #8
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    Youre right....On demand no jumper pin. I looks for what is called a delta T between the two thermisors. The unit has a preprogrammed map for a certain outdoor ambient, this temp means too cold must have ice or still warm enough to be no ice. That is why yours is reverted to the min time and deforosting all the time.

  9. #9
    ok...and you ohmed the sensors correct?

  10. Quote Originally Posted by amasuperbike View Post
    The unit has a preprogrammed map for a certain outdoor ambient, this temp means too cold must have ice or still warm enough to be no ice. That is why yours is reverted to the min time and deforosting all the time.
    So it might be the coil sensor getting too cold so the board thinks it has ice on it, thus limiting the air flow on the outdoor unit? Would that be the symptoms of an undercharged or overcharged unit in heating mode?

    Best!

  11. #11
    make sure the sensor is in the correct place on the coil

  12. Quote Originally Posted by kytech77 View Post
    ok...and you ohmed the sensors correct?
    Yup, I ohmed the sensors and they were a little bit off the chart, but not by much. My laser probe gave me -2 oC on the ambient probe.
    The ambient sensor gave me 27Kohms, which is around 2.5 oC. The coil sensor gave me around 32Kohms or 0 oC. Should I be worried?

  13. #13
    is your outdoor coil dirty?

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