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  1. #1
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
    Posts
    62

    Question Sanity check on maintenance

    All,

    I just had a yearly "checkup" on my heatpump (Trane XL15i), and they said the subcool was high (28), which does seem high (here are all the "deets")

    OD Temp: 42
    ID Temp: 69
    SL Temp: 40
    DL Temp: 75
    Head PSIG: 330
    Suction PSIG: 66
    Subcool: 28
    Superheat: 29

    So, they suggested that the Filter drier is most likely clogged. Which, I'm cool with paying to have them replace, that's fine. My question is, looking around online, this would seem to be the opposite of the case. Too high a subcool, from what I can find, generally means overcharged system doesn't it? And as you'll note below, last year was fine, and refrigerant doesn't just osmose into the system, so the likelihood of an overcharge seems remote.

    Could it be that the guy just didn't let the system run long enough, or...?

    Looking at the numbers from last year, my subcool was 16 on a 48F day, which apparently is right where it should be.

    I'm obviously not looking to do this myself, and I have a tech scheduled to come out and do a real diagnosis on Monday, but I want to make sure I don't get talked into something that just doesn't make sense. Any help would be appreciated, and better would be an explanation for why this is either right or wrong.

    Thanks very much! Let me know if you need additional data.

  2. #2
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    I assume this is an R410A system. Model numbers?

    Has the technician verified proper airflow?

  3. #3
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
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    62
    yup, R410A.

    Heatpump: 4TWX5030A1000AA
    AH: 4TEE3F39A1000AA

    And no, I don't think so. He had cleaned the coils prior. I know that's mentioned in various places, but I'm not sure how you measure the airflow on the HP... amp draw on the fan motor? In which case, yes. But curious. Or do you mean air flow from the AH, in which case no as well, though the indoor filter had been changed.

    Thanks!

  4. #4
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    Quote Originally Posted by staze View Post
    yup, R410A.

    Heatpump: 4TWX5030A1000AA
    AH: 4TEE3F39A1000AA

    Thanks!
    It could be a restriction, but it's still worth ensuring the airflow was properly set on that air handler (the 39 is factory set to provide ~1400 cfm). Let us know what the technician finds Monday.

    The system has a factory installed filter drier. Was one installed external to the unit?

  5. #5
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
    Posts
    62
    Really, all of this is going off the yearly maintenance guy, where an actual repair tech/diagnosis is going to happen monday, but I don't want to just be told "yup, clogged drier, it'll be $$$" if that doesn't make any sense at all. Also, love the chance to learn something on all this. I understand the basic cycle of how a HP works and all that, but more knowledge is always a good thing.

    Pricing isn't allowed

  6. #6
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
    Posts
    62
    Pretty sure, yes. It's on the liquid side I believe (the smaller, non-insulated copper tubing) just after the tubing "leaves" the HP and heads up into the house. Looks like this: http://www.allenrefrigeration.com/Filter-Drier.html. Says it's for 410A, and also says it's reversible.

    So, it could be a restriction... anything else it might be?

  7. #7
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
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    62
    Pricing isn't allowed
    I understand, it was an example... but thanks. sorry about that.

  8. #8
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    3,371
    It's hard to diagnose anything over the internet, but perhaps someone else will offer a guess at what the problem may be. That filter drier should not have been installed, and it would not surprise me if that is the one that is clogged due to brazing without nitrogen. Please keep us updated. You have a nice system, and I hope it gets fixed quickly and properly. Good luck -- in the mean time, are you using AUX heat?
    Last edited by RyanHughes; 02-15-2013 at 10:32 PM.

  9. #9
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
    Posts
    62
    the system still works fine, and I was told it wasn't a problem to keep using it, it's just a bit less efficient. is it a problem running it with a high subcool?

    I'll have to ask about the extra filter drier being installed. it's been there since April 2007 (when the system was installed). Still very curious if anyone else has any ideas.

    So, in short, it's not likely it was just improperly measured (system hadn't run long enough, was set wrong, etc)?

  10. #10
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    As a check: any noticeable temperature differential across the extra filter drier on the liquid line? May not be easy to physically check, but a restriction will often cause such.

    Running it a couple more days like this, especially in milder weather, probably isn't a problem; compressors are pretty tough. I would agree with that. Certainly less efficient.

    By the way -- how long did the tech run the system? Hopefully more than 10 minutes...

  11. #11
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
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    62
    Well, no idea how long it's been like this is the thing, other than it could have been 14 months (time between checkups). But yeah, guess a couple more days isn't really that much comparatively. Makes me wish I had a thermocouple for my multimeter.

    They mentioned noticing a temp difference across the drier. So yeah, guess that's likely it. I'd ask a likely repair cost (ballpark) for that, but we know where that leads. =P

    So if they replace it, I should obviously make sure they're using nitrogen for the soldering?

  12. #12
    Join Date
    May 2007
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    DC Metro Area (MD)
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    Quote Originally Posted by staze View Post
    Well, no idea how long it's been like this is the thing, other than it could have been 14 months (time between checkups). But yeah, guess a couple more days isn't really that much comparatively. Makes me wish I had a thermocouple for my multimeter.

    They mentioned noticing a temp difference across the drier. So yeah, guess that's likely it. I'd ask a likely repair cost (ballpark) for that, but we know where that leads. =P

    So if they replace it, I should obviously make sure they're using nitrogen for the soldering?
    Yes, they really need to use nitrogen (~5 psi inert gas to prevent oxidation) when brazing. It takes a bit more time, but it is important if you want to avoid a similar problem down the road. You should insist upon it in my opinion. This system isn't that old? As long as you have a factory installed LL filter drier you do not need or want a second filter drier -- another potential for restriction and pressure drop across the liquid line.

  13. #13
    Join Date
    Mar 2008
    Location
    Willamette Valley, Oregon
    Posts
    62
    okay, I'll ask about just not having it, or removing it. I'm guessing they put them on all the systems as part of their standard install... but who knows.

    So, how do they test for a clog, per se? Just going by temp rise across the drier, and assuming everything else is fine, it must be clogged, so close off the lines, drain them down, remove the drier, and replace? (then recharge the system). I'd assume they're not going to care what it's clogged with and therefore not know why it clogged in the first place?

    I'll make sure to insist on nitrogen.

    I'm assuming that there's little chance the system is low on charge given the symptoms (and numbers)? Just trying to avoid extra costs here...

    Oh, and are they going to have to replace the built-in one as well, since they're "opening" the system?

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