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  1. #1
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    213

    Low SH, mfg suggested SC?

    Saw this today when I was mentally kaput already.

    TXV. Package. R410. Suction sat, 45 F. Suction line, 50 F.
    Liquid sat, 114 F. Liquid line, 97 F. Mfg suggested SC for
    ambient of 100 F, 17 degrees, so it was spot on.

    Unit actually cooling fine. But from what resident
    said, it sounds like it was maybe shutting down on
    compressor overload previous day.

    I think I remember indoor WB about 62 and DB 78 F.
    Actually, liquid sat pressure was initially about 390 psig.
    I cleaned condenser coil and pressure dropped to whatever
    114 F sat is.

    The low, 5 F, superheat is what bugs me. Should a TXV
    have that low of subcooling for 100 F ambient?
    (My charging table for fixed orifice with these indoor/outdoor
    temps does suggest 5 F superheat, but I thought TXVs operated
    more safely, with a larger superheat as a rule.

    Had a mercury thermostat and a lady that plays with it a lot.
    Someone suggested that compressor could start up backwards
    and result in overheating? Does that sound plausible for
    230 V, single-phase?

  2. #2
    Join Date
    Jun 2004
    Posts
    896
    Did you say it was a package unit?
    I would check txv bulb first
    Make sure its not loose
    Make sure it insulated.
    is the txv adjustable?

    I've seen scroll reverse before from short cycling.

    Install a digital stat with 5 min delay

  3. #3
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    213
    Yes, package.

    Sensing bulb seemed secure. It had that gooey beef-jerky-like
    pipe wrap on it.

    I didn't check to see if the TXV was adjustable. It had that
    big nut-like appearance thing on it, but I don't know if
    that is a reliable indicator for adjustability. I have
    never adjusted one.

    It is good to hear another vote for the reversing compressor
    idea. I thought it sounded far-fetched when they suggested
    it to me.

    Thank you.

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,766
    R410A at 390psig is a sat of 115F, so the condenser wasn't really dirty since 114 is a sat pressure of 385.8psig. At 78DB and 62Wb indoor conditions, you had very little load on the unit. Thats only a RH of 40%.

    Might want to put a time delay relay on it to make sure its not from the thermostat being played with.
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  5. #5
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,844
    Quote Originally Posted by georgelass View Post

    Unit actually cooling fine. But from what resident
    said, it sounds like it was maybe shutting down on
    compressor overload previous day.
    What was the description they gave you? Was the unit running, just not cooling? Was the unit off completely? ...

    Sounds like air flow may be low, as well as a low load condition. Txv's do have their limitations.

    As Beenthere suggested, make sure the comp delay is selected on the thermostat.

    I did have a unit that would attempt to restart within a couple minutes, due to poor home insulation. It would trip the properly sized breaker. The OL should trip before the breaker, but not always.
    I installed a hard start and new comp under warranty. In testing, the new comp would trip OL every time with the new comp when short cycled. The hard start cured the issue. I also selected the comp delay on the stat. No more problems...

    If the unit does have a start kit, check to make sure the pot relay isn't sticking closed. If it doesn't open, it will trip the OL. Check the bleed resistor on the start cap. If it's bad, your relay is likely failing.
    "The only true wisdom is in knowing you know nothing" Socrates

  6. #6
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    213
    Quote Originally Posted by mgenius33 View Post
    What was the description they gave you? Was the unit running, just not cooling? Was the unit off completely? ...

    Sounds like air flow may be low, as well as a low load condition. Txv's do have their limitations.

    As Beenthere suggested, make sure the comp delay is selected on the thermostat.

    I did have a unit that would attempt to restart within a couple minutes, due to poor home insulation. It would trip the properly sized breaker. The OL should trip before the breaker, but not always.
    I installed a hard start and new comp under warranty. In testing, the new comp would trip OL every time with the new comp when short cycled. The hard start cured the issue. I also selected the comp delay on the stat. No more problems...

    If the unit does have a start kit, check to make sure the pot relay isn't sticking closed. If it doesn't open, it will trip the OL. Check the bleed resistor on the start cap. If it's bad, your relay is likely failing.
    The owner and relatives said the unit had started blowing warm air. One relative hosed
    the outside coil and the unit started working again, leading me to believe the compressor
    had MAYBE shut off on its overload. Earlier this year, a disconnect fuse had blown but
    airflow, amp draws, temp differences, all seemed okay. I don't remember if I checked amp
    draw upon initial start-up. But it is two years old and a scroll. Do those even need startup kits?

    And now that I think about it, while getting HERS tested on some split systems (package units
    don't need the refrigerant checked), the minimum superheat (allowed) is down around 5 F degrees
    and we've only seen lower on one unit (condenser) severely overcharged from the factory. So I
    am now concluding, as suggested above, that TXVs do allow such low superheats. My memory
    is going even as I slowly gain experience.

    The plan is currently to return to the house and install an (inexpensive) non-mechanical thermostat
    with the built-in delay. Whoever installed the unit had tried to get the homeowner to use the new
    digital thermostat but homeowner found it too complex. Yes, a delay-on-make installed
    at the contactor would serve the same purpose but doesn't provide the same feedback
    (a blinking snowflake) to the owner that the digital thermostat would.

    Okay. Thank you all for making me feel more comfortable.
    And I want to mention that I tried searching for this subject but dial-up makes
    it very tedious because "TXV, superheat" get mentioned in a lot of threads.
    Again, thank you for your patience and understanding.

  7. #7
    Join Date
    Sep 2012
    Location
    Central Florida
    Posts
    892
    Quote Originally Posted by georgelass View Post
    The owner and relatives said the unit had started blowing warm air. One relative hosed
    the outside coil and the unit started working again, leading me to believe the compressor
    had MAYBE shut off on its overload. Earlier this year, a disconnect fuse had blown but
    airflow, amp draws, temp differences, all seemed okay. I don't remember if I checked amp
    draw upon initial start-up. But it is two years old and a scroll. Do those even need startup kits?

    And now that I think about it, while getting HERS tested on some split systems (package units
    don't need the refrigerant checked), the minimum superheat (allowed) is down around 5 F degrees
    and we've only seen lower on one unit (condenser) severely overcharged from the factory. So I
    am now concluding, as suggested above, that TXVs do allow such low superheats. My memory
    is going even as I slowly gain experience.

    The plan is currently to return to the house and install an (inexpensive) non-mechanical thermostat
    with the built-in delay. Whoever installed the unit had tried to get the homeowner to use the new
    digital thermostat but homeowner found it too complex. Yes, a delay-on-make installed
    at the contactor would serve the same purpose but doesn't provide the same feedback
    (a blinking snowflake) to the owner that the digital thermostat would.

    Okay. Thank you all for making me feel more comfortable.
    And I want to mention that I tried searching for this subject but dial-up makes
    it very tedious because "TXV, superheat" get mentioned in a lot of threads.
    Again, thank you for your patience and understanding.
    Is it possible that unit went out on low pressure?? If it did it would start working again once pressures stabilized inside of the unit. I have seen in the shop faulty TXV's that cause the unit pressure to slowly drop till they cut out on low pressure switch. Just a thought mind you.

  8. #8
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,844
    Do scroll comps need a hard start, maybe not in most cases. However, if there are issues like this, I can't think of a reason that it would hurt.
    I installed a KickStart kit with pot relay on my scroll unit when it was brand new. Nine years, and the run cap is still good.
    I know many believe that the starting current doesn't have anything to do with bad run caps, but I think that adding a start kit helps reduce the risk of many potential issues.
    "The only true wisdom is in knowing you know nothing" Socrates

  9. #9
    Join Date
    Oct 2012
    Location
    CA
    Posts
    418
    I know that goodman requires a hardstart to be added to a split system that also has a txv kit installed on the indoor unit . I ran into this on a split heatpump back in 2007 when the compressor would not start back up mid day in the summer .

  10. #10
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,312
    Quote Originally Posted by 54885488 View Post
    I know that goodman requires a hardstart to be added to a split system that also has a txv kit installed on the indoor unit . I ran into this on a split heatpump back in 2007 when the compressor would not start back up mid day in the summer .
    Specifically, any TXV that is non-bleeding, or where the long lineset guidelines suggest it.
    So, if you were putting a goodman unit, on a SpaceHack system, then you wouldn't need one, if the long lineset guidelines are not in effect.


    George, I'm failing to see the problem with the system.
    5* superheat, although seemingly a little low, is acceptable by some manufacturers.

    It sounds to me, like you have a customer with a itching thermostat finger, as others have mentioned.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  11. #11
    Join Date
    Oct 2012
    Location
    CA
    Posts
    418
    Yea it was a non bleeding type . It was a goodman furnance with a cased coil and txv kit. Whats a spacehack ?

  12. #12
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,312
    Quote Originally Posted by 54885488 View Post
    Yea it was a non bleeding type . It was a goodman furnance with a cased coil and txv kit. Whats a spacehack ?
    More correctly known as a "space pak", or a manufacturer of high velocity systems.

    "SpaceHack", because you got no space, so you gotta hack it in.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

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