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  1. #66
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,280
    Quote Originally Posted by mark beiser View Post
    Hey Andy!

    True, but they sure are nice to have for more skilled techs too.
    Also better for the system at our normal summer operating conditions since we spend a lot of time in the "--" range on superheat charging charts.
    I think TXV's are a good thing... they solve a lot of issues a piston will not accurately address.

    Remember the old adage 'one size fits all'... ever try that with shoes or a shirt? Yeah, one large enough will do... but do you really want to walk around in size 15 EEEEE wooden boxes; or stuff your 12D feet into 10B canvas? Or perhaps we would look more professional wearing a gunny-sack in place of our proper fitting workshirts?

    With metering of refrigerant; a TXV will meter more accurately over a wide range of demands... where a piston is just a middle of the road compromise.

    In my climate where temps can range over 30+ degrees; and we can be sticky humid, then rain, then sticky humid again--all in one day.... Expecting a piston to handle all those indoor climate changes... well IMO the customer gets the short end of that deal.

    This is not aimed at anyone, just my opinion: If the tech staff does not understand TXV's (proper installation and proper charging)... then perhaps they need some professional training???
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  2. #67
    Join Date
    Nov 2011
    Location
    Charleston, Wv.
    Posts
    1,499
    had to work on a 1 year old 4 ton york, MC inside and out, 410A, fixed orifice. System is leaking, we were told to add charge. It took a VERY long time for the superheat to start to come down to target. Subcooling was normal in short order though.

    I'm thinking the next fixed orifice MC I have to charge is gonna be done by subcooling. What do you guys think about that?? I guess you run the risk of incorrect charging, but if it's a matched system, you should still end up pretty close. Also, we were only getting about a 16 degree difference in supply/return air....I thought it should have still been closer to 20. that was at 76 room temp.

    I may have been over complicating things, as i hadn't had any experience with the MC's.

  3. #68
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    498
    only problem with txv's are they are now not as reliable as they were once. We are having to change out entirely too many. For this reason i would be glac to go back to piston or fixed metering devices.

    dogboy


    Quote Originally Posted by ga-hvac-tech View Post
    I think TXV's are a good thing... they solve a lot of issues a piston will not accurately address.

    Remember the old adage 'one size fits all'... ever try that with shoes or a shirt? Yeah, one large enough will do... but do you really want to walk around in size 15 EEEEE wooden boxes; or stuff your 12D feet into 10B canvas? Or perhaps we would look more professional wearing a gunny-sack in place of our proper fitting workshirts?

    With metering of refrigerant; a TXV will meter more accurately over a wide range of demands... where a piston is just a middle of the road compromise.

    In my climate where temps can range over 30+ degrees; and we can be sticky humid, then rain, then sticky humid again--all in one day.... Expecting a piston to handle all those indoor climate changes... well IMO the customer gets the short end of that deal.

    This is not aimed at anyone, just my opinion: If the tech staff does not understand TXV's (proper installation and proper charging)... then perhaps they need some professional training???

  4. #69
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,280
    Quote Originally Posted by DOGBOY View Post
    only problem with txv's are they are now not as reliable as they were once. We are having to change out entirely too many. For this reason i would be glac to go back to piston or fixed metering devices.

    dogboy
    Literally EVERY item in every product has issues once in a while. This does not mean they are bad items... just issues... like anything else.

    I remember when Firestone built bad tires... does that mean we should stop having rubber tires on cars? Of course not.

    TXV's have been used in refrigeration and AC for longer than any of us have been alive... they are a tried and proven technology.

    Just because we get some poor quality ones from China does not mean the technology is bad... just we need to not buy cheap stuff from China.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  5. #70
    Join Date
    Nov 2000
    Location
    Lancaster, Pennsylvania
    Posts
    885
    TXV's are tried and proven but the quality is rather poor today. Given the option on an evap, I will not use one.
    KX500......the original big green meanie

  6. #71
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,280
    Lessee... we sacrifice the quality of a better design... simply because a few run-offs are sub-quality.

    I guess we need to go back to solid rubber tires because inflatable tires have flats.

    Just about EVERY system I install has a TXV on it. And when I mount a dry charge AC unit (always insist on a 13 SEER coil) I always add a refrigeration quality Danfoss R-22 TXV (adjustable). After setting the SC, I go back to the evap and set the SH. Systems work like a champ, and I have NEVER had a call-back on a TXV I custom installed.

    Yes, I had a couple of bad TXV's on Ruud coils in 2010... however the distributor gave me a new coil and paid me some labor to change it. I hear trane had bad blower wheels, Goodmana has all kinds of bad electric and electronic parts, and lets not forget the MC coils...

    Again: The technology is not bad... just a few items. Better to not throw out the baby with the bathwater... unless we are too lazy to see if there is a baby in the pan.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  7. #72
    Join Date
    May 2005
    Location
    Indianapolis
    Posts
    21
    Quote Originally Posted by gravity View Post
    I'm pretty sure if you tried to pump the unit down, the condenser coil wouldn't have enough volume to hold all the refrigerant. you might be able to pump some of it down.

    I have also heard these units are critical charge. if there overcharged by 6oz they can trip on high head.

    This just isn't a good thing with all the non-skilled hvac guys that dont know how to properly charge a unit and gauges/temp clamps that havent been calibrated for years.
    So is this a problem with the systems or with the personnel installing and servicing them?

  8. #73
    Join Date
    May 2005
    Location
    Indianapolis
    Posts
    21
    Quote Originally Posted by mh heating View Post
    I just checked out the microchannel coils for Nordyne. What a nightmare. Im doing a new construction job right now and am planning on installing a nordyne system. Looking at they're "quick data reference sheet" (match AH to OD unit) I have to add an additional 29 oz right off the bat. Then add for the additional lineset.

    Now if Im installing a a 3.5 ton 14seer hp with the new c7 MC coil, I have to change the orfice to an field supplied txv and add 29oz. But heres the kicker, you have to change the outdoor units orfice from .55 to a .57... How stupid is that

    Might have to reconsider using nordyne equipment on future jobs.

    MH
    By way of responding to this situation, Nordyne is making a running change, with a new service valve. This service valve will incorporate the restrictor inside the valve as opposed to inside the distributor. The new valve will provide the flexibility necessary to accommodate multiple indoor products. Your distributor can refer to the tech bulletin dated May 1, 2012.

  9. #74
    Join Date
    Jun 2001
    Posts
    3,910
    Oh gawd. Those will be a pain to clean.

    Back when my wife and I ran a large paper route, our van's evap coil would get a build up of paper dust on it every year or so, and it was a royal pain to clean. Brushing only makes it worse IMHO.
    Governments don't tax to get the money they need, governments will always find a need for the money they get. Ronald Wilson Reagon

    Born Again KA

  10. #75
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,243
    Quote Originally Posted by timkav View Post
    So is this a problem with the systems or with the personnel installing and servicing them?
    Since this thread started back up I have to say this is a problem with the systems. No system should be designed so sensitive as to not account for minor variations. There is no way that a system can be perfectly charged in the field no matter how skilled the tech is. We do not work in a controlled environment. SH & SC take about 15 minutes to stablize if not longer. In that time the indoor wet bulb can change a few degrees & then your numbers won't be totally accurate again. If you get two excellent techs charging the same unit under different conditions there is no way they would both put in the exact same amount of refrigerant in the system. Sure they'll get close but with a system with 5 lbs. of gas where a few ounces make the difference between working & not that is absolutely ridiculous.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

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