Page 1 of 3 123 LastLast
Results 1 to 13 of 27
  1. #1
    Join Date
    Jul 2006
    Posts
    613

    SUB Cooling adjustment

    This is on a 3 year old Amana 3 ton TXV R410A HP system. The TXV crapped out this past week. A new TXV valve was installed at the AHU. The sub cooling is low by approximately 6 degrees, do you add refrigerant or adjust the TXV? The original refrigerant charge was pulled into the CU and re-used. The unit was working fine until the TXV crapped out. Much more detailed info can be provided, but I just would like a general answer in this case. This equipment is clean and like new. There are no issues with airflow, etc. I do not think it is worth wasting 220 oz of refrigerant to prove the refrigerant charge is 100% correct by recovering it and weighing in new. Do I add some refrigerant or tweek the TXV?

    Thanks for any info.

  2. #2
    Join Date
    Sep 2009
    Location
    Hampton, GA
    Posts
    444
    Check manufacturers spec on the unit. And based on that if the subcool is lower then their guidelines then your undercharged. If it's over then your overcharged. Typical subcool settings are 10-12 subcool.

  3. #3
    Join Date
    Jun 2011
    Location
    Hammond,La.
    Posts
    1,176
    You aren't going to get 100% of the refrigerant pulled into the condenser on a pump down. You would have to look at the superheat, vsat, lsat, pressures, etc to also see what may be going on. Make sure that you have good bulb contact and it's insulated and it would depend on the TXV, is it adjustable?. 6* of subcooling on 410a doesn't equate to much refrigerant on most units of that size at normal temperatures so you may just need to add a bit after you have let the unit run a while to stabilize. Not going to get much detailed help in this section though.
    "I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it."
    Benjamin Franklin, 1766

  4. #4
    Join Date
    Jul 2006
    Posts
    613
    You are right, the unit was not stabilized, I'll check it in the morning. I did not give detailed info and I did not request it. The pressure left in the lines and AHU coil after the pump down did not amount to a good fart, let alone to any amount of refrigerant loss. Not to be a S....A.. here, but why would I ask about a TXV adjustment if the TXV was not adjustable? I stated SC was 6 degrees below spec....,maybe that was unclear in my first post. Yes, I work in the field. I think we will stop this thread now. I just had a simple question for what for some should be a simple answer.

  5. #5
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    You don't adjust the TXV to change the subcooling...
    If more government is the answer, then it's a really stupid question.

  6. #6
    Join Date
    Jul 2006
    Posts
    613
    I tried thanking you twice for the information you posted. My replies have not yet posted for me. I'll stop answering... I did think that on a TXV system that since you went by subcooling and verified superheat that you could adjust the TXV for subcooling. I agree that most TXV's are set dog on close from the factory. This old Parker ...9068 POS was an exception.

  7. #7
    Join Date
    Jul 2006
    Posts
    613
    Mark, I had to go back and read more info. I guess you could be right, but you could be wrong. In a single stage application, If SH and SC both are low or high, it say's adjust the TXV. It has more information.

  8. #8
    Join Date
    Sep 2009
    Location
    Hampton, GA
    Posts
    444
    Quote Originally Posted by riderman View Post
    You are right, the unit was not stabilized, I'll check it in the morning. I did not give detailed info and I did not request it. The pressure left in the lines and AHU coil after the pump down did not amount to a good fart, let alone to any amount of refrigerant loss. Not to be a S....A.. here, but why would I ask about a TXV adjustment if the TXV was not adjustable? I stated SC was 6 degrees below spec....,maybe that was unclear in my first post. Yes, I work in the field. I think we will stop this thread now. I just had a simple question for what for some should be a simple answer.
    rofl... sorry I read your post off my phone...didnt see the part about you saying the subcool is low by 6 degrees. LOLL , good luck.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,818
    Quote Originally Posted by mark beiser View Post
    You don't adjust the TXV to change the subcooling...
    In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.

    OP. Recover the charge and weigh it to find out if it has the correct charge. Then use the refrigerant you recovered to recharge the unit. No need to use virgin.
    Contractor locator map

    How-to-apply-for-Professional

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

  10. #10
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,506
    Quote Originally Posted by beenthere View Post
    In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.
    I can't even remember the last time I adj. a txv on a res. system, but I want to say in the late 70's, and that was to only get the way out of wack SC and SH correct. [/QUOTE]
    Last edited by Mr Bill; 06-02-2013 at 08:55 AM.
    __________________________________________________ ____________________________
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein

    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  11. #11
    Join Date
    Feb 2005
    Location
    In a van by the river
    Posts
    618
    Quote Originally Posted by beenthere View Post
    In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.
    I wonder what the logic is behind that. It's not adding up in my head how it is recommended on an undercharged system to increase TXV SH setting in order to get subcooling and then magically expect the TXV to maintain a reasonable superheat once refrigerant is dumped into it.
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

  12. #12
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,506
    Quote Originally Posted by git-r-dun View Post
    I wonder what the logic is behind that. It's not adding up in my head how it is recommended on an undercharged system to increase TXV SH setting in order to get subcooling and then magically expect the TXV to maintain a reasonable superheat once refrigerant is dumped into it.
    __________________________________________________ ____________________________
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein

    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  13. #13
    Join Date
    Dec 2004
    Location
    Grand Rapids, MI
    Posts
    587
    I read the instructions before I adjust the TXV, but seems to me the opening or closing of the valve changes both the SH and the SC.
    I believe you should adjust for the SH first then fill till proper SC.
    luck dan

Page 1 of 3 123 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