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  1. #40
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    Oct 2016
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    Maybe it is the TXV as well.

    One time I was working on a Lennox RTU that had 2 circuits of cooling. The suction was low on both stages, both stages had pretty much the exact same problem, they were still working but not correctly and I didn't think both stages could have the same identical problem. I figured it couldn't have been the txv because what's the chances both stages have the same exact issue where the txv was semi working. Although replaced both filters dryers as well when doing the txvs.

    I thought it was an air flow issue at first but in the end I replaced both txvs and my pressures were spot on for both stages.

  2. #41
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    Apr 2010
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    Austin,Texas
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    If the unit has an outdoor txv, there might be a check valve coming out of the distributor. With all the work you've done, if its there, I can almost guarantee the little screen sock is plugged up. That'll give you low pressure in cooling mode only, if you weighed in the charge and checked all the other things.

    If you know where it is, fire the thing up, and stick your hand in there right on it. Bet its freezing cold.


  3. #42
    Join Date
    May 2014
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    Bay Area California
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    My guess is the screen on the indoor TEV.


    Quote Originally Posted by CHAINIK View Post
    If the unit has an outdoor txv, there might be a check valve coming out of the distributor. With all the work you've done, if its there, I can almost guarantee the little screen sock is plugged up. That'll give you low pressure in cooling mode only, if you weighed in the charge and checked all the other things.

    If you know where it is, fire the thing up, and stick your hand in there right on it. Bet its freezing cold.
    I don't understand happiness as an ambition . . . It's not really worthy. I understand it as a byproduct.

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  4. #43
    Join Date
    Aug 2017
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    Thread Starter
    Waiting for the new txv, also ordered a check vale and filter dryer as well being they was inexpensive. The check valve is a round looking copper piece with an inlet and outlet, kind of weird looking to me, but anyhow.

  5. #44
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    Apr 2010
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    Austin,Texas
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    Quote Originally Posted by BBeerme View Post
    My guess is the screen on the indoor TEV.
    I haven't worked on a whole bunch of these, and I'm sure there's variations, but the ones I'm familiar with have a TXV in the compressor compartment, and a piston inside. Now that I think about it, the piston was in a screw in fitting on the distributor, so I guess that assembly could be made with a TXV option in mind. Just never saw one that had one. But, keep in mind, I was national accounts, so I saw a lot of the same types of units across multiple locations. YMMV.

    Quote Originally Posted by Sipperman View Post
    Waiting for the new txv, also ordered a check vale and filter dryer as well being they was inexpensive. The check valve is a round looking copper piece with an inlet and outlet, kind of weird looking to me, but anyhow.
    So it does have one. Like I said, if its got low pressure in cooling mode only, that's almost certainly the problem.

    The ones with this problem I've worked on, the previous techs would always change the drier, then get the same problem, and start grasping at straws, reversing valve, txv, restricted evap coil, etc. But they never fixed the problem, just eventually gave up. Eventually, I noticed that the filter drier is only utilized in heating mode, and the check valve and it's sock is used in cooling mode. I don't know if it helps any, but I began, after any repair work, to start them up in heating mode first. The idea being that if any junk was in the piping, the larger filter drier would trap it, instead of the strainer.

    I stumbled across that check valve problem after beating my head against everything else. Maybe its something that every Trane tech already knows about, but it felt like discovering some long lost manuscript of esoteric knowledge when I figured it out.


  6. #45
    Join Date
    Aug 2017
    Location
    Las Vegas
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    I like to do the drier, check valves, reversing valve, and the compressor. The symptoms do indicate it being a txv, after you changed the reversing valve. Sounds fun, hopefully your customer is ok.

  7. #46
    Join Date
    Aug 2017
    Location
    Kansas City, MO
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    Quote Originally Posted by Push It View Post
    It is common in my company to always change a reversing valve when you change a compressor in a heat pump. Is this not common in the industry? I personally like changing it to avoid this type of situation. Gas is recovered, compressor is out of the way, all your tools are out, etc.
    I've not heard of this before.... but sounds like a decent idea, if parts are available, and it doesn't cost the customer too much extra.

  8. #47
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    Aug 2017
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    Quote Originally Posted by pitbull14218 View Post
    Maybe it is the TXV as well.

    One time I was working on a Lennox RTU that had 2 circuits of cooling. The suction was low on both stages, both stages had pretty much the exact same problem, they were still working but not correctly and I didn't think both stages could have the same identical problem. I figured it couldn't have been the txv because what's the chances both stages have the same exact issue where the txv was semi working. Although replaced both filters dryers as well when doing the txvs.

    I thought it was an air flow issue at first but in the end I replaced both txvs and my pressures were spot on for both stages.
    I had a newer Lennox unit with 4 stages, with high discharge temperatures, and low suction pressures across all 4 stages. I ended up replacing all 4 TXV's. I had another Lennox unit with two stages, maybe 10 years old with similar symptoms and i again replaced both TXV's. This is something to look out for with Lennox units.

  9. #48
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    Jul 2010
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    Just to toss out what I like to do with RV change outs.

    I know many guys do this and I've seen in mentioned on hvactalk a few times.

    Cut 6 or so inches of pipe out of the unit on each line coming off the RV. Braze in the correct lengths of new pipe on the new RV outside of the unit with a coupler brazed on the end(or swage if size permits)

    Then install in the unit. It's much easier to get those RV joints brazed in quickly and correctly outside of the unit.
    “Free men do not ask permission to bear arms.”
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  10. #49
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    Aug 2017
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    Thread Starter
    That is something i do, thanks for the input.

  11. #50
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    Aug 2017
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    Quote Originally Posted by Brian8383 View Post
    Just to toss out what I like to do with RV change outs.

    I know many guys do this and I've seen in mentioned on hvactalk a few times.

    Cut 6 or so inches of pipe out of the unit on each line coming off the RV. Braze in the correct lengths of new pipe on the new RV outside of the unit with a coupler brazed on the end(or swage if size permits)

    Then install in the unit. It's much easier to get those RV joints brazed in quickly and correctly outside of the unit.
    This advice can turn a nightmare reversing valve replacement, into a smooth quick and easy dream.

  12. #51
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    Aug 2017
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    Thread Starter
    Amen to that

  13. #52
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    Oct 2016
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    Quote Originally Posted by Brian8383 View Post
    Just to toss out what I like to do with RV change outs.

    I know many guys do this and I've seen in mentioned on hvactalk a few times.

    Cut 6 or so inches of pipe out of the unit on each line coming off the RV. Braze in the correct lengths of new pipe on the new RV outside of the unit with a coupler brazed on the end(or swage if size permits)

    Then install in the unit. It's much easier to get those RV joints brazed in quickly and correctly outside of the unit.
    Not a bad idea, probably harder to purge with nitrogen though

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