Page 1 of 2 12 LastLast
Results 1 to 13 of 15
  1. #1
    Join Date
    Apr 2012
    Posts
    7

    High Head Low Suction PXV Problem?

    Alright guys/gals I would like to get an online diagnosis of my problem. I am a home owner with a 2 year old Lennox 14ACX System. I am not in the industry but have some technical ability. It is currently cooling the house in Houston, TX fine but I had a Tech come out and do a “spring check up” just to see if there was anything wrong with the original install. He found that there was only a 16 degree split when cooling. 71 return and 55 supply when it should be 20-23 degree drop. I have plenty of return air, clean condenser/evap and filters. I will list the technical info below

    Log Compressor amps
    S 39
    R 14

    Condenser fan amps 1.0

    410A

    Super heat
    50 degrees
    80 psi

    Sub cool
    20 degrees
    310 psi

    Blow ramps 6.6

    TXV 39L72 -- TXV kit (R410 a/c) 3.5-5 Ton
    Links to direct purchase sites are not permitted.

    The technician said that the temp drop was underperforming and the superheat / subcool data was telling us that there is a blockage at the TXV, either stuck in place or there is debris jamming it. The super heat / subcool are obviously both way out of tolearance along with the return and head psi. We checked temps on each side of the filter / drier which is located on the liquid side and they were identical. We popped on a hard start kit to see if that would unjam the TXV and that did not have any affect so we removed it. At that point he said I needed to replace the TXV because the evap was being starved. I decided to do some investigative work myself. I do not have a pressure gauge set but I do have an instant read thermometer. I took a reading on the return side and then stuck it in the supply side. While checking the thermometer I took off all the insulation from the TXV valve and bulb and held the bulb firmly in my hand warming it up considerably. After about 5 minutes I did not see any change whatsoever in the supply temp. Again I have no way of checking the return pressure.

    Questions

    Could the TXV be adjusted? Is this an adjustable TXV?

    Do I need to replace this TXV? Am I going to destroy the compressor if I don’t?
    Last edited by beenthere; 04-29-2012 at 05:56 AM. Reason: removed link

  2. #2
    Join Date
    Dec 2010
    Location
    Woodbridge Twp, NJ
    Posts
    1,308
    Sorry, no DIY on this site is allowed. I suggest you call a professional.
    Every customer you take for granted today will be someone else's tomorrow.

  3. #3
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,071
    Quote Originally Posted by bhermis View Post
    We popped on a hard start kit to see if that would unjam the TXV and that did not have any affect so we removed it.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  4. #4
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,721
    Have your tech replace it ,it is a straight forward repair

  5. #5
    Join Date
    Apr 2012
    Posts
    7
    I do not intend to do any of this work myself and am not asking for DIY information. I am asking if this is an adjustable TXV and if so would adjusting it be of any use, or is it jammed? I would have a HVAC professional come out and do it. I am also asking if the corrent situation, though not ideal, is still OK.

  6. #6
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,071
    Those pressures are way to low for 410A on both sides, did the tech ever think it might just be low on charge?
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  7. #7
    Join Date
    Apr 2012
    Posts
    7
    The Tech said specifically " I could add 1lb of coolant but it would not do any good" He specifically said that the suction was too low and the head was too high indictating a blockage at the TXV valve.

  8. #8
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Quote Originally Posted by Mr Bill View Post
    Those pressures are way to low for 410A on both sides, did the tech ever think it might just be low on charge?
    With a 20 degree subcool it looks like he dumped some in to see if his suction would come up.
    You're only as good as your customer will allow you to be.........If they want junk, sell them junk, but make your junk look neat!!!

  9. #9
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Quote Originally Posted by bhermis View Post

    Could the TXV be adjusted? Is this an adjustable TXV?

    Do I need to replace this TXV? Am I going to destroy the compressor if I don’t?
    NO.........NO.......YES.......YES

    if you held the bulb in your hand for five minutes and no change occurred then the valve is stuck. Let the guy do his job and change it out.....it's probably under warranty anyway!!
    You're only as good as your customer will allow you to be.........If they want junk, sell them junk, but make your junk look neat!!!

  10. #10
    Join Date
    Apr 2012
    Posts
    7
    So this valve 39L72 is not externally adjustable? I will destroy the compressor with this high head low suction if I do not replace it? I just don't want to jeopordize the rest of the system by opening it up to replace this valve if there is a simpler solution.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,317
    Quote Originally Posted by bhermis View Post
    So this valve 39L72 is not externally adjustable? I will destroy the compressor with this high head low suction if I do not replace it? I just don't want to jeopordize the rest of the system by opening it up to replace this valve if there is a simpler solution.
    While what you posted points to the TXV. Only a skilled on site tech can check to know for sure if its the TXV.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #12
    Join Date
    Apr 2012
    Posts
    7
    I got a second opinion on it and after reviewing the readings the 2nd tech agreed that the TXV needs to be replaced. The part is under warranty so he will pump down the system, replace the valve, replace the filter/dryer and recheck pressures/temperatures. Anything else I should make sure he does? I was getting a 15 degree split before. Assuming normal operating conditions, proper sized coil/condenser, clean filters and proper charge, should I expect a 20 degree split from a Lennox 14ACX system when he is done?

  13. #13
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,942
    Cool first guy is right. Any reason why you went with the second?

    The delta T depends on the sensible and latent loads. There is no split expectation without the proper measurements.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event