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  1. #1
    Join Date
    Sep 2006
    Posts
    95

    help with pressure drop

    I was called out in the fall I found the condenser txv bulb was broke off. Now they have someone staying there and want it fixed. I went to local armstrong dealer got txv put it on. Run great in heat. As soon as you switch over to ac the pressures, both head and suction, Fall to 0 fast. Pressures taken at the lineset.
    So I pulled the indoor orfice it was clean, I took the coil loose and blew nitrogen through it. It apeared to be open. So I started calling friends all of them say coil stopped up. Boss said coil stopped up Change it out, I changed it out I still have same problem.
    I called the armstrong dealer and checked part numbers they said they give me the wrong txv. The one I need has a different superheat. I ask if this was a txv for a heat pump or straight cooling. they said heat pump. My problem is the condenser superheat shouldn't matter as long as it is bypassing in a/c. Now Im going to next town over to get another txv from armstrong dealer. and try it out on monday. any ideals will be of great help

  2. #2
    Join Date
    Feb 2007
    Location
    Central MD, Carroll County
    Posts
    88
    if the system is a heat pump the outdoor metering device is bypassed in cooling mode. The cause of the pressure drop seems interesting usually when there is a restriction you can run a low suction and high head. Im asuming that your indoor coil is using a fixed metering device? Regardless of that Im wondering if your running into a vacum as if you left the suction service valve closed like you were pumping the system down. A lot of od txv's incorporate check valves which assist the change of flow of refrigerant in heating and cooling

  3. #3
    Join Date
    Sep 2006
    Posts
    95
    Yes it is like pumping the freon back in the condenser.
    it is a heat pump with a fixed orfice on inside coil.
    armstrong dealer said it is wrong txv, but is for a heat pump. So it should be bypassing in a/c.

  4. #4
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    yes its pumping itself down, (liquid line restriction)



    .

  5. #5
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,667
    Try to get some more info on the txv if it has a check valve in it , if it works ok in heat mode then the txv is allowing flow to the condenser but when it reverses it should reverse flow unless it stopped by a check valve.

  6. #6
    Join Date
    Apr 2008
    Location
    On the roof
    Posts
    136
    Sounds like an issue wth the check valve
    If you didn't do it right the first time it probably makes sense that your here asking the right way to do it now

  7. #7
    Join Date
    Feb 2007
    Location
    Central MD, Carroll County
    Posts
    88
    youll have to excuse my earlier post I was waking up. Anyway I myself am leaning to an issue with a check valve you could use a magnet to see if it moves freely but again if armstrong thinks they they have sent you the wrong one they may have. A lot of check valves are now incorportated with the od txv. Id not worry about it until monday when you install the part. And for the record I meant to say it was like you had the liquid service valve blocked off.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,786
    I had a supplier give me a TXV they dsaid was for heat pumps. Did the same thing you described.
    It didn't have an internal bypass in it. It needed a an external bypass.
    YThey might have done the same thing to you.
    Contractor locator map

    How-to-apply-for-Professional

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

  9. #9
    Join Date
    Sep 2006
    Posts
    95
    Beenthere was right, changed out txv everything working good. It didnt have an internal check valve. Thanks everyone for your help

  10. #10
    Join Date
    Apr 2004
    Posts
    7,680
    When talking about a heat pump with someone you call for help, you need to specify not only the head pressure, but which valves you are connected to. In heating mode you have two head pressures and they are likely to differ but tell alot, in cooling you have two suctions and they should be the same but important to know non-the-less.

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