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  1. #14
    Join Date
    Jul 2012
    Location
    Richland, WA
    Posts
    248
    I remember it them saying that you want the TEV/TXV to see the true saturation temp otherwise it could open the TEV/TXV to much, or close it done to far. And for resi there are no service valves by the TEV/TXV

  2. #15
    Join Date
    Jan 2012
    Location
    WEST COLUMBIA S.C.
    Posts
    286
    Most charging charts say to get within 3-5degrees super heat. It seems that the 12 2 o'clock position compared to 3 O'clock position wouldn't change that to much

  3. #16
    Join Date
    Jul 2012
    Location
    Richland, WA
    Posts
    248
    Quote Originally Posted by hewitt View Post
    Most charging charts say to get within 3-5degrees super heat. It seems that the 12 2 o'clock position compared to 3 O'clock position wouldn't change that to much
    Wouldn't think but, I just remember what the power points for the books said, and what all the instuctors said.

  4. #17
    Join Date
    May 2008
    Location
    Myrtle Creek. Oregon
    Posts
    182
    I am from old school! any where except top or bottom.
    a stupid question is a question you wont to ask, but don't

  5. #18
    Join Date
    Jan 2012
    Location
    WEST COLUMBIA S.C.
    Posts
    286
    Nate state different from what u were instructed.My instructor stated 3,9 like I posted. Maybe some others will follow up on this.How long have u been out of school.

  6. #19
    Join Date
    Jul 2012
    Location
    Richland, WA
    Posts
    248
    Graduated in January


    Sent from my iPhone using Tapatalk

  7. #20
    Join Date
    Jan 2012
    Location
    WEST COLUMBIA S.C.
    Posts
    286
    Cboe congratulations on being old school, help the new school. Great old school car on your profile

  8. #21
    Join Date
    Nov 2011
    Location
    USA
    Posts
    392
    Quote Originally Posted by alamo1718 View Post

    The question is; Does a TXV bulb always have to be in contact with the piping? What will happen if it isn't?
    The answer to the first question is "yes". The purpose of the TXV, in the first place, is to generate and maintain a relatively constant superheat value. It can do that only by comparing the saturated evaporator temperature to the suction line operating temperature. The sensing bulb is the part of the valve assembly that "sees" the suction line temperature. The gas in the bulb expands and contracts with changes in temperature, so the suction line temperature is "converted" to a pressure. The saturated coil temperature is determined by the suction pressure, via the pressure/temperature relationship of refrigerants.

    The bulb pressure creates an opening force, pushing on one side of the diaphragm while the suction pressure creates a closing force, pushing on the opposite side of the diaphragm. When the two forces balance, the superheat "setting", determined by the spring force, is accomplished.

    If the sensing bulb isn't in contact with the suction line, the bulb temperature, in most cases, would be greater than the actual suction line temp. So, the valve would "see" high superheat and open up, flooding the coil. But the actual superheat would be low, or non-existent.

  9. #22
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,369
    In the past, I had a seasoned tech tell me the little tit (or the pinched off copper) @ the sensing bulb makes a difference in the mounting of the bulb. Something about traping freon in cap tube of sensing bulb. I have read several txv installation guides and can find nothing to support this. Is this BS or maybe a design flaw that has been corrected.

  10. #23
    Join Date
    Nov 2011
    Location
    USA
    Posts
    392
    The explanation I heard was the "tail" is positioned "up" when bulbs are mounted vertical, to keep any liquid in the bulb and away from the diaphragm.

  11. #24
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    548
    While we are on the subject, what is everybody's thoughts on mounting the bulb on the vertical line set. I know it's technically wrong, but have sen many systems like that and they all seam to control SH just fine. It would seam to me that a vertical line would be ideal, as no oil can sit in the line, the refrigerant would be superheated anyways so there should be no liquid in the horizontal line to begin with

    Thoughts?

  12. #25
    Join Date
    May 2012
    Location
    NC
    Posts
    50
    Thank you everyone, especially satuatedpsi.
    So, I'm going to return and remove the TXV, install a a piston, vacuum and charge to SH. I suspect a visiting Super installed TXV's to fix problem systems.
    For my future reference, is it acceptable to move the sensing bulb outside the air handler, installed on suction line and insulated well? It's not in an attic, just a free return closet. I've recently seen this elsewhere but did not ask if they had performance issues with the system. I think this is what lkjoel is asking also, i'm just specifying outside of the air handler. I hadn't considered vertical vs horizontal.

  13. #26
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    548
    Quote Originally Posted by alamo1718
    Thank you everyone, especially satuatedpsi.
    So, I'm going to return and remove the TXV, install a a piston, vacuum and charge to SH. I suspect a visiting Super installed TXV's to fix problem systems.
    For my future reference, is it acceptable to move the sensing bulb outside the air handler, installed on suction line and insulated well? It's not in an attic, just a free return closet. I've recently seen this elsewhere but did not ask if they had performance issues with the system. I think this is what lkjoel is asking also, i'm just specifying outside of the air handler. I hadn't considered vertical vs horizontal.
    My question was not about inside plenum vs outside plenum, that makes little difference, providing its insulated. In my experience a well insulated bulb outside the duct work works better than an uninsulated bulb in the duct work

    My Question was in regards to the bulb being on a vertical section of line vs a horizontal, from what I have been told, this is frowned upon (bulb on vertical line) but nobody can seam to tell me why

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