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Thread: Outdoor TXV?

  1. #1
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    516

    Outdoor TXV?

    HL8B36 with an AVG36 air handler, Arzel HPPro zone control

    Attic – horizontal right
    Airflow on the AH is programmed for 1200/800
    3 zone system with a ‘dump’ zone that is always open (4 6” runs) and a bypass (supply to return – about 12’ long)
    RA temp - 72
    SA temp – Didn’t write this one down and forgot. Likely well into the 90s as the Arzel SA temp sensor read 89 before I crawled back there.
    Total ESP 0.65
    The unit has locked out multiple times on either high dis temp or high press
    During operation the suction side remains at around 60psi while the high side climbs from 300 to 600+ over the course of about 15-20 minutes. The following numbers were taken while the unit had been running for about 7 minutes
    LLP – 345 and climbing
    LLT – 78.9
    Discharge press – 315 (why is discharge lower than LL?)
    SLP – 60
    Suction line temp at TXV bulb / before accumulator – 44
    Suction line temp at compressor / after accumulator – 4 (?)
    Frost forming immediately on outdoor distributors and on coil after about 5 minutes

    Some things that don’t make sense to me but I’m pretty certain that the TXV is restricted. Bulb position was correct and well insulated. In hind sight I should have removed and squeezed but I didn’t… Any thoughts appreciated

  2. #2
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    516
    410a BTW

  3. #3
    Join Date
    Nov 2011
    Location
    USA
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    406
    I can make some observations. The SST is around 10˚ which would be about right for 30˚ OD max. The superheat is way high for a TXV system. Frosting distributor lines would indicate low refrigerant flow. And the subcooling is high IMO. All of which would confirm your suspicions about the valve. But restrictions don't cause excessive head pressures, unless someone else overcharged the system trying to get the suction pressure up, which would be my guess. Or, the airflow on the indoor coil is low too.

    The 4˚ temp between the accumulator and compressor is temporary, due to liquid boiling off in the accumulator.

    The difference in discharge and LL pressures would seem to defy the laws of Physics.

  4. #4
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    516
    ODT was 50

    I figured was the case with the accumulator. I didn't take the press reading difference from discharge to liquid my self so it could be backwards or who knows.

    Unit was recovered and factory charge weighed in

    I can't see airflow being a problem with the static pressure and a variable speed drive, i think it should be delivering. It could be airflow in certain zone situations but the symptoms were present will all zones calling. The unit ran fine in air conditioning.

    I think that the TXV is most likely the problem. You're right that it could still be overcharged. I have seen a few of these units this year and they have all been overcharged with no other problems, but under the same load conditions, the suction on those units ran around 115psi. So over charged on or not, i think i'm set on the TXV. Thanks for your input it's very much appreciated!

  5. #5
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,789
    Sounds like a TXV, and or a bi flo LLFD that is restricted in the heating flow direction.

    Dump zone also open?
    Contractor locator map

    How-to-apply-for-Professional

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

  6. #6
    Join Date
    Mar 2012
    Location
    West Chester, PA
    Posts
    516
    Yes that zone has 4 6" runs which are always open. I didn't think to check the FD but that's a good call. Again frost was at distributors but could still be getting a drop at the drier. Thanks

  7. #7
    Join Date
    Jul 2010
    Location
    Eastern Kentucky
    Posts
    55
    Im curious, What happened after you changed the TXV. and this may sound really silly but is it possible your heating elements are located before the indoor coil. Maybe they are cycling on introducing a source of heat to coil and driving up head pressure sky high lol

  8. #8
    Join Date
    Jul 2010
    Location
    Eastern Kentucky
    Posts
    55
    So if your discharge pressure is 315 then your liquid line coming back from coil is 375 then something is maybe heating that coil up? lol I dont know , but that is strange though

  9. #9
    Join Date
    Jul 2010
    Location
    Eastern Kentucky
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    55
    Nevermind my last post lol stupid thinking. even if the coil is heated that extra pressure should still show at the discharge pressure

  10. #10
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,480
    restricted txv or clogged drier.

    run the unit in cooling and check discharge pressure and then liquid line temp at service valve. this will tell you if the filter drier is restricted.

    in heating you will see a higher subcooling then cooling due to the "condenser"(indoor) coil being smaller.

    everything you have indicates starved "evaporator"(outdoor) coil which would either be txv or drier.

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