txv
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Thread: txv

  1. #1
    Join Date
    Dec 2012
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    nc
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    txv

    Grandair heat pump(nordyne). Three ton split system txv at indoor coil
    In heatpump mode as far as I know the discharge pressure and the liquid line pressure should be the same, the only difference is the refrigerant comes back to outdoor unit is condensed but it should still be close to the discharge pressure. After hooking up my gauges i found the discharge pressure (r410a) around 325psi(110F) and liquid line was around 125psi(40F) and my suction (third port straight into compressor) also around 100psi (outside temp was around 50 degrees).
    also line set temp at indoor are 140 degrees and and after txv liquid line 89degrees, so is heat getting trapped due to the restriction?
    Can somebody tell me if this is right, a bad txv? or is it normal?
    Heat pump will run for hours even when it reaches set temp, if it was a bad t stat and heatpump was running continously it would make sense that it will rise the temperature to inconfortable levels but temp remains the same. Is this due to the txv?
    When return air was 74 degrees the supply temp was 94degrees, should it be better or normal for heatpumps.

    did not run heat strips when i looked at it.
    Worked in the hvac for a few years, always intalled and learned a little service on the way, can i get some answers on my questions from the pros?

  2. #2
    Join Date
    Feb 2009
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    Tallahassee, FL
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    Does nordyne use outdoor ll valve for piston like carrier?

  3. #3
    Join Date
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    nc
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    Quote Originally Posted by SBKold View Post
    Does nordyne use outdoor ll valve for piston like carrier?
    it uses a piston at the outdoor unit,

  4. #4
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    Need more info. It sounds like you have a stuck check valve indoors.

    Is the piston at the liquid line valve outdoors? If so, when you hook your gauges up, you actually are reading after the metering device. So your readings are null.

    Definitely need more info. We're shooting darts in the dark

  5. #5
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    Dec 2012
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    nc
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    yes, the piston is at the liquid line valve at the outdoor unit it inserted at the connection of the liquid valve nut and the valve itself. And know that you said that, im thinking i am reading the same pressures as at the true suction port. I did get confused since on the goodmans the discharge and the liquid lines are always the same or around the same pressure but goodman meters the refrigerant after the liquid valve inside the unit. one question, (at the indoor coil) why is the (3/4) lineset around 145 degress and the liquid line only 89 degress, since the txv is not suppose to meter shouldnt the liquid line be around the same temp?

  6. #6
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    Jul 2009
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    Columbia, MD
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    No. In heatpump mode. The hot gas from compressor is going to the indoor coil which is now the condenser coil. It is being subcooled and returned back to outdoor coil(evaporator) to be metered.

    The indoor txv does not meter in heating. there should be a check valve or the TXV has an internal check built into it.

    think of cooling mode. if you touch the discharge line of compressor it is very hot. when it leaves the condenser coil it is cooler to the touch. same thing happens in heating mode inside.

  7. #7
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    Dec 2012
    Location
    nc
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    right, the piston at the outdoor is what meters in heatmode not the txv at the indoor. so should the liquid line be the same temperature as the discharge line of the compressor? the discharge line of the compressor gets really hot to where i cant even keep my hand on it, but the liquid line that returns the refrigerant from the indoor coil to the outdoor unit is only 89 degrees that i can hold it not that hot. should i see that temperature drop from the condensing of the refrigerant. and thanks for the patience

  8. #8
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    We will have to chat more on the pro side of the site.

    Turn in some credentials of your employment to site and get pro approval.

  9. #9
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    Dec 2012
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    nc
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    ok,

  10. #10
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    Jan 2004
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    Lancaster PA
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    The liquid line should NOT be the same temp as the compressor discharge line.
    Contractor locator map

    How-to-apply-for-Professional

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

  11. #11
    Join Date
    Nov 2011
    Location
    USA
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    359
    The piston located in the liquid service valve explains the 125 psi reading. Last time I remember measuring a system like that, the pressure was some higher than the true suction.

    Saturated suction temp is low 30's, which is reasonable for 50˚ OD. The supply and return temps indicate a good ∆T across the coil. The fact it runs all the time at 74˚ setpoint could simply mean that's all it can do. At 50˚ OD, the heat output is about 36K Btu's. Maybe the the structure's losing 36K Btu's at 50˚ OD.

  12. #12
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    Thanks, thats what i wanted to hear.

  13. #13
    Join Date
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    At 50 od the unit is definately doing 36k if not more? If it were 30 than its output would be less but not at 50. So how will it do then?

    The difference between the two readings was the distributor/coil pressure drop.

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