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  1. #1
    Join Date
    Oct 2005
    North Carolina
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    I had a sevice call from an owner that had no cooling on a 2 ton Trane XL14i (R410A) heat pump. It was determined that the compressor had gone bad because there was no pressure differential and it was only drawing 3 amps. I replaced the compressor and noticed that the suction pressure was around 50 psi and the head pressure was climbing to almost 500 psi when it finally tripped on high head. I then tested the system in heat mode and the pressures looked normal at 135 suction, 300 head. Ambient temperature was 74 DB/67WB.

    I then tested the sensing bulb on the indoor TXV by placing it in warm water and switched it back to the cooling mode. The head pressure stabalized at around 250 psi. While I was testing the bulb, the outdoor unit would trip off and on, most likely on head pressure. I strapped the sensing bulb back on the suction line with insulation and closed the unit back up. I ran the system in cooling and had the same pressure readings (50 suction/500 head) until it tripped off on high head pressure.

    I'm suspecting that if it is a bad TXV, this could have resulted on his compressor failing after only 3 years. Is it most likely the TXV or could it be something else?

  2. #2
    Join Date
    May 2000
    Indianapolis, IN, USA
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    Sure has the symptoms of an indoor TXV throttling too far shut. I can see it damaging the compressor. That would be a recip, could be valves or a broken rod.

  3. #3
    Join Date
    Feb 2005
    Dothan, Al
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    I can't see how the TXV can cause high head. If the TXV is not opening, its like a restriction - can't cause high head, as far as I know.
    I would think reversing valve or indoor check valve leaking by. Of course the check valve is probably in the TXV, so then that would make the TXV bad.


  4. #4
    Senior Tech Guest
    Restriction on high side = Low suction/high head.

  5. #5
    Join Date
    Nov 2001
    lorain county,Ohio
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    had two this summer doing same thing,one was bad 410 txv,
    other one our sales/install crew had gotten and installed
    r-22 coil. these were not heat pumps though.

  6. #6
    Join Date
    Apr 2004
    Niantic, Illinois
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    We have had this debate before about the head pressure being high or not in a restricted situation. It came to a stalemate and nobody could make a definitive point. As to the txv, you are correct, I have seen exactly this many times. It usualy is on factory installed txv that the installer didn't lift the bulb off the pipe or wrap it with wet cloth or anything to to keep from overheating the bulb. Sometimes this makes the txv fail at startup, if not it still reduces the life of the txv by a bunch. The installers opinion is usualy "Hey, it was working fine at start up, I never cool the bulb and they fire up fine".

  7. #7
    Join Date
    Jan 2004
    Midlothian, Virginia
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    bad txv

    I was taught that a bad txv on evaporator initally causes high head and then it goes down after the refrigerant is pumped down behind the txv that won't fully open.

    This was what I was told. The txv won't open enough and the compressor pumps down the refrigerant behind the txv. Most of refrigerant is in the liquid line behind the txv. it's not feeding enough. Low suction pressure is observed along with high superheat, poor cooling of compressor,and cycling of compressor on low pressure or high heat. The head is high only high till the heat is squeezed out of refrigerant in condenser, head drops after most of refrigerant is is in liquid form backed up behing txv.

    So the compressor has little load from high side and some load from suction and hence a lower than normal amp draw.
    Be carefull a compressor may not be bad it may have low load with bad txv.
    Goodbyee stranger it's been nice. Hope you find your paradise! Hey it aint rocket science, "It's a Trade !"

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