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what should i charge to when replacing the TXV

long story short lennox unit bad txv wouldn't adjust 30 degree superheat found brass shavings inside the txv.

I ended up flushing the lines changing the filter dryer and txv. i used an Emerson txv instead of another lennox txv. now my question is, do i charge the system to the condenser requirement of a 6 degree approach and 3 subcool or what Emerson wants a 10 degree subcool?


  • zepfan
    zepfan Member Posts: 309
    In my experience 10 degrees of sub cooling will rarely get you in trouble no matter whose unit you are working on.good luck
  • unclejohn
    unclejohn Member Posts: 1,700
    I'd go with the equipment manufacture recommendations. But as Zep said 10* sub cool shouldn't hurt.
  • NYplumber
    NYplumber Member Posts: 503
    If I recall, @Techman posted a year ago about subcool based off of your vertical height from the condenser. There is a formula behind the madness.
  • JStar
    JStar Member Posts: 2,752
    I still get my charge close by superheat with a TXV, but verify subcooling. In fact, I do that on every system.
  • Techman
    Techman Member Posts: 2,144
    edited July 2015
    Mcro, There aren't too many places in a system to get brass shavings, possibly they were copper?
    Yea , KindaSorta, 10*SC will cover your butt for every AC for every brand . So going by the CYA rule then you will be OK. So, if your system "needs" only 2*SC , CYA and get 10*SC, or if your system "needs" 8*SC then 10*SC will still CYA. Its a "catch all" rule, for "typical" installs, that fall within the "piping height vs length" chart of each Mfrg . Don't a few CU say on their nametags 6*SC is their "target SC", 6*SC sure limits the piping "H vs L" thing.
    Q here, the ACTUAL REQUIRED SC of a 50' horizontal lineset is the same REQUIRED SC as a 50' lineset that goes up vertical 35'. NO WAY ,NO WAY, NO WAY.
    My BIGGEST concern was/is the fact that lots and lots of Techs don't know the REAL story of SC , or worse they DON'T CARE. If all they do is typical residential/light comm then they CYA and do the "Target SC thing" and they are "good to go", I agree mostly/ some times. I come from a more Commercial/Industrial background (Carrier, Governaire) and "knowing" how to FIGURE OUT SC was/is normal. Now, all of these #'s and charts and guidelines are ALL FOR ONE REASON ONLY, and that is to ensure that the TXV/metering device has a "FULL LL " feeding the TXV, under all "normal" operating conditions. Having a full SGMI at the CU does not guarantee a full SG at the TXV. I've put SGMI at the TXV and CU on some systems "just to see" or I use my "electronic SG tool" to "see" whats happening at the TXV.

    There are still Techs that say that just USING a SGMI WILL cause the system to be overcharged. HOGWASH. Overcharging a system is due to an "un-knowledgeable" Tech, plain and simple
  • Empire_2
    Empire_2 Member Posts: 2,343
    WOW all the abbreviations......... Yea, I'm lost. Print it in Aerobic. At least I can go on line a decipher it...:-) Hey Terry Only kidding. What is a CU?, You are talking 1 adem 12....
  • Lance
    Lance Member Posts: 142
    Evacuate, weigh in the appropriate charge. Adjust for pipe length and airflow to achieve proper indoor delta T. Lennox has the charts and info. Weigh in gets it right every time.
  • John Mills_5
    John Mills_5 Member Posts: 935
    Lennox does like a lower subcool than some. We put in an Allied heat pump the other day, under the conditions, called for 1° subcool! Personally I think do what the condenser manufacturer calls for, they know the system.
  • Empire_2
    Empire_2 Member Posts: 2,343
    John am I reading you right? 1 *Sub/cool? Min 8* 10-14 w/ tx more like it. If that were the case, ( not knowing what you are actually looking at) Just pipe the discharge line into 4 linear foot of coil and there you go. I respectfully would like to know your source of that information because it is and makes no sense.


    Mike T.
  • Empire_2
    Empire_2 Member Posts: 2,343
    edited August 2015
    I have never seen a 1* S/C.......

    Mike T
  • John Mills_5
    John Mills_5 Member Posts: 935
    That was correct, they wanted 1° subcool under the conditions we had at the time. We were surprised. It's a chart right on the door of the unit. 2 ton 14 SEER heat pump.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    edited August 2015
    I see a range of 8-10 subcool on the Trane 410a stuff, nomenclature states plus or minus 3. Finding 12 is the sweet spot, with low 50s discharge temps. Recently got the SMAN3, we have a tempestuous relationship, as I'm acclaimating to the precision of it, learning to trust it!
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