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  1. #1
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    Way to Determine if a TXV is Present?..



    Is there a way to check or test if a Thermostatic Expansion Valve might be installed on an AC evaporator coil? Replacing an old 3 ton Compressor / Condenser unit with a newer higher efficiency R-22 SEER 14, 36,000 BTU condenser unit. It is not practical to replace the air handler at this particular time. The evaporator coil of this AC split system is built into metal ductwork above a natural gas heating furnace with forced air blower. It is not a proper AC air handler, just an inverted V evaporator coil & drain pan permanently installed into the up-flow air discharge ductwork. Due to expediency and exceedingly poor existing workmanship, there no way to gain access to the coil short of destroying and rebuilding much of that ductwork. Replacing all the homes existing ductwork is a project for another year.

    There is no practical way to determine the size, model, installer, manufacturer or other features of that evap. coil, but it was very recently a fully functional part of a working 3 ton central AC split system. R-22 refrigerant has been recovered, system evacuated, purged and sealed with low pressure Nitrogen in preparation to swap that condenser out and change its location. For purposes of recharging the system with R-22 and estimating correct super-heat, is there a non-invasive way to guess if that evaporator is using a fixed orifice or a built-in Thermostatic Expansion Valve?..



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    Re: Way to Determine if a TXV is Present?..

    Check the rate of pressure equalization after compressor is stopped. TXV system is much slower than orifice system.

    BTW, you should done that before evacuation!
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  3. #3
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    Re: Way to Determine if a TXV is Present?..

    Can you drill a viewing hole in the metalwork and put an endoscope camera in there to have a look see?
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    Re: Way to Determine if a TXV is Present?..

    Usually a txv won't let the suction pressure get above a set pressure, say 140psi, if you put nitrogen in the liquid line side and watch the suction pressure it should rise and then stop it its a txv (unless its a bleed port type)
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    Re: Way to Determine if a TXV is Present?..

    Does the condensor unit have a reciever?

    Some of the smaller/low capacity units don't always have a reciever even with an xv?

    Like Brian says you need to cut a hole to insert a camera or better still to access the evaporator coil not just to check whether or not, but to make further adjustments. Which you'll probably need to as it sounds like a botch up, and if the holding pressure drops, it could mean that the coil could be perforated with leaks!
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    Re: Way to Determine if a TXV is Present?..

    Thanks for that useful information. That’s just what I was looking for! I'll get set up shortly to inject dry Nitrogen into the capped liquid line and monitor increasing pressures carefully. Some would appear to not fully grasp the full meaning of the terminology "non-invasive"!..

    Existing evaporator coil and line set do not leak at present, they have been previously tested to standard R-22 operating pressures, else I would not be leaving it in place for the time being. Regarding the presence of a receiver, certain experts could likely better determine that than I... My suspicion is that the old condenser does not, it is a Heil 2CU35 series, perhaps late-eighties. The newer condenser with only two years of service replacing the old Heil, is a Trane XL14i 3 ton R-22 AC unit dated 2009.

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    Re: Way to Determine if a TXV is Present?..

    Invasive can be the only way in circumstances where no other information is available, and you can't make an omlette without breaking eggs.

    If you choose not to be invasive, then when you have finished fitting your new condensor and successfully or unsuccessfully re commisioned the system. Then only you yourself will know whether or not to choose to be invasive? Fingers crossed choice won't be an option.

    Good luck with your project.
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  8. #8
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    Re: Way to Determine if a TXV is Present?..

    Invasive can be the only way in circumstances where no other information is available, and you can't make an omlette without breaking eggs.

    If you choose not to be invasive, then when you have finished fitting your new condensor and successfully or unsuccessfully re commisioned the system. Then only you yourself will know whether or not to choose to be invasive? Fingers crossed if its an xv without an off load bleed, then choice shouldn't be an option.

    Good luck with your project.
    50 hertz but 100s worse

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