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  1. #1
    Join Date
    Jul 2010
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    Vancouver
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    TXV/Check Valve Stuck Open


    I'm having a problem with the TXV (or internal check valve) getting stuck open on a new Goodman heat pump. I was measuring high suction pressure (~135-140psi, R410A), slightly high amp draw (10.5A when sheet indicates 9.5A for these conditions), and no superheat. I tried adjusting the TXV to increase the superheat, and the control did nothing. Placing the bulb in ice water did nothing either.

    I reset it to the factory setting, and set the system to heat for a few minutes, then back to cool, and the TXV started working. However, it gets stuck open again after several hours operation. The liquid line has a slight rumbling or shaking feeling when it's stuck. So far it's happened 4 times. I was hoping it was simply some debris that would get caught in the filter/drier, but that doesn't seem to be the case. The last time I freed it up, I had to tap the TXV while in heat mode to free it up, simply operating in heat wasn't enough.

    I've attached some graphs of the suction line temperature near the evaporator, and a picture of how the TXV is installed (TXV.jpg). Could the TXV mounting orientation cause any problem, perhaps the check valve is getting stuck open? The TXV manual simply says don't mount it power head down.

    Gets Stuck.png Shows two on cycles of the unit, proper operation on the first one (with TXV hunting), and stuck open on the second one. At some point during the off period or right at turn on, the TXV or check valve got stuck. Notice the different slopes of temperature when the system turns off. The turn-off where it got stuck also looked different from turn offs where it worked properly the next cycle.

    3rd fix.png Shows switching the unit between heat and cool to fix the problem. The first (not shown) and second attempts didn't work, and show a fast drop in temperature when heat is turned off. The 3rd attempt works, and shows a much slower drop in temperature.

    There are a couple of other less major problems. The first is TXV hunting, shown in Hunting low and high.png. The first half is low stage, the second half is high stage. It gets much better in high stage cool. The pressure variation is about 2-3 psi in low stage. I'll have to try moving the bulb and see if that helps.

    The second problem is a distinct hissing sound produced by the condensing unit, only when in high stage cool and with the TXV operating properly. This hiss does not appear in low stage, or in high stage when the TXV is stuck. It's hard to tell for sure, but it may be coming from the discharge muffler. The hissing is much less pronounced, but still there when in high stage heat.

    Any suggestions you could provide would be greatly appreciated.

    Regards,
    David
    Attached Images Attached Images



  2. #2
    Join Date
    Dec 2009
    Location
    New Zealand
    Age
    40
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    59
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    5

    Re: TXV/Check Valve Stuck Open

    I have had similar problems with reversable systems , if you are going to recover gas and pull **** apart you may as well change both indoor and outdoor check valves and be done with it. Txv is hardly ever the problem .

  3. #3
    Join Date
    Jan 2010
    Location
    USA
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    Re: TXV/Check Valve Stuck Open

    what did you use to make the graphs ? I have had a lot of problems with txv/ being restricted. Have been looking for a more positive way of knowing the valve is bad.

  4. #4
    Join Date
    Jul 2010
    Location
    Vancouver
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    Re: TXV/Check Valve Stuck Open

    I've cleared it up a few more times, but it still eventually gets stuck again, so I'm just going to replace the combo TXV/check valve assembly. I think Andy's right, I really don't think the TXV is the problem, it definitely seems like a stuck check valve.

    I made the graphs with Flukeview Forms along with a Fluke 189 logging multimeter and a thermocouple.

    David

  5. #5
    Join Date
    Jan 2009
    Location
    jax, fl,
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    Re: TXV/Check Valve Stuck Open

    What is your subcooling ? you check that when running a txv, there are no check valves if it is a new goodman r410a heat pump. subcooling should be 7-9 degrees and superheat also. bet you are overcharged.

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