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The Thermostatic Expansion Valve

The other one

Comments

  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    The Thermostatic Expansion Valve

    The TXV, or TEV, is an often misunderstood system component. In reality, however, the TXV is a relatively simple component that has only a one line "job description". The ONLY purpose of the TXV is to maintain constant evaporator superheat. It does not maintain evaporator pressure. It does not maintain system capacity.

    IT'S ONLY JOB IS TO MAINTAIN EVAPORATOR SUPERHEAT

    If you are out there troubleshooting an air conditioning or refrigeration system and your superheat readings are correct, please leave the TXV alone!

    Excessively high superheat readings can be caused by a system undercharge, liquid line restriction, clogged filter drier or clogged inlet strainer on the TXV.

    When evaporator superheat is high on systems that are equipped with thermostatic expansion valves, the valve is likely open all the way but there is not enough refrigerant available to be fed to the evaporator. So, if the superheat is high, check the refrigerant charge, check for restrictions, check for blockages, check everything..... except the poor TXV!
  • TechmanTechman Member Posts: 2,144
    TXV's

    Hi Eugene! Well said ,about those pesky TXV's! The darn things last 20 years or so,no screw ups,and once set PROPERLY, they don't need any readjustments for 20 years or so also. I just can't seem to find that many "BAD" TXV's
  • Greg SwobGreg Swob Member Posts: 167
    txv types

    Eugene- I'm not sure I understand what advantage a non-bleed type txv (or hard shut-off) offers vs. a bleed back style. Could you please enlighten?
  • Eugene SilbersteinEugene Silberstein Member Posts: 1,380
    One of the main

    One of the main differences is that metering devices that allow the system pressures to equalize during the off cycle enable the equipment manufacturers to use lower torque motors in the compressors as they do not have to start up with a large pressure difference across the compressor. Systems with, for example, capillary tubes typically have compressors with low starting torque.

    I'm running out of the house right now but will post some more goodies later on.
  • TechmanTechman Member Posts: 2,144
    TXV

    Greg In any system that has a non-equalizing TXV,the compressor manufactorer usually requirers the use of a "hard start kit " The compressor will start against an un- equalized pressure,between hiside and lowside
  • Greg SwobGreg Swob Member Posts: 167


    sorry- double post!
  • Greg SwobGreg Swob Member Posts: 167
    I understand

    the hard start requirement, but why on earth do some manufacturers insist on non-bleed type TXV's in the first place? It causes a high torque start, resultingin the need for a hard start. But, is there any advantage to a non-bleed TXV? What is gained? Does it prevent refrigerant slugging the coil? Thanks!
  • TechmanTechman Member Posts: 2,144
    TXV's

    Greg. Alot of commercial refrigeration systems operate on a "low pressure" control, which means the TXV has to be a "non bleed" type.The temp of the refrig unit slowly raises as does the pressure in the low side of the system.The bleed style TXV would allow the loside press to rise rapidly,causing the comp to come on again,long before the refrig case actually warms up.
  • Jeff Lawrence_25Jeff Lawrence_25 Member Posts: 746
    Well,

    I don't think this one will maintain anything.
  • don_163don_163 Member Posts: 67
    those we

    find to frequently on outdoor units.But I'll take one that fail closed, over one thats over feeding any day.

    Good find Jeff.


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