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  1. #1
    Join Date
    Oct 2019
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    High head high suction air dryer

    Dear forum, this is my first own thread here
    I usually come here to find my questions and solutions.

    I'm English native. I am a tech working with HAVC field. I got a called from customer to test Air-dryer machine not cooling and the pressure always dripping (high and low pressure switches with different circumstances) . The first I checked the condensing coil it is pretty clean then I hooked up my guage and see liquid line pressure close to 450psi and suction line 110 psi. It's 2hp system with R407C refrigerant. I thought it's overcharged so i free some but the pressure won't drop. Its use TXV TCHE. At first I suspect TXV is bad but after testing TXV doing it job just fine( I tested sensor bulb with heat and ice). I stopped supply wet air into air inlet valve then System is run fine with pressure drops to 60psi low side and 220-230 psi on the liquid line. I hooked thermometers to suction line and temperature reading of 7c. I supply wet-hot air back the head and suction pressure raise up to the pressure I mentioned above(it's around 7 mins). By just disconnected air-inlet from reservoir tank anf allowed wet-hot air to flow across evaporator coils the pressure run back to what It's expected to be(290psi liquid line and 80psi suction). I try to vacuum and recharge the results still the same. I swap new compressor in(cuz i think it's bad suction valve) but 🙃 no luck to drop head and suction pressure while supplying wet-hot air to reservoir tank. So can you all suggest me a solution? Forget to mention the system is running for 3 years old without any problem And no one touched it for servicing or repair after the first installation date. I do Preventive maintenance every 6 months to it.

  2. #2
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
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    Sounds like to much load possibly, does the system use any kind of restricter to measure in air supply? Get your posts up and apply for Pro status and we can help you more, cant troubleshoot in the open forums, but testing your sensing bulb in with heat or cold doesnt mean it's working correctly

  3. #3
    Join Date
    Oct 2019
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    Thread Starter
    Thank you for your prompt reply. The system doesn't have pressure regulation at inlet valve to evaporator coil but it do have oil filter and pressure guage after air flow out of evaporator coil(filter just has been changed so there is no restrictions). The pressure reading high air-flow from evaporator to free space but system is fine with that circumstances. If i hook air from evaporator outlet valve to reservoir tank the problem happen(compressed air>air-dryer>reservoir tank>o2 generator). Sensing bulb testing is not in proper test but its does seem it does it job since it worked properly if the air is free. Does these info i provided helpful for helping troubleshoot in open forum?

  4. #4
    Join Date
    Feb 2005
    Location
    Florida
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    Did you weigh the charge in?

  5. #5
    Join Date
    Oct 2019
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    Thread Starter
    Yes I did. I even tried started with low charge 1Kg to 1.55kg (labeled 1.55Kg of R407c)
    It seem that TXV allowed liquid line bypass thru to vapor line because subcooling is super high 30C. But I even tried replacing TXV and found out that it's was sticky open but sh$t it's work only if the wet-air not connected to reservoir tank. If I try connecting it to reservoir to store my dry air the liquid pressure raise up rapidly until high safety pressure switch opened. Till now it seems TXV is sticking again. Have no idea what to do more.

  6. #6
    Join Date
    May 2013
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    Quote Originally Posted by Tika View Post
    ... pressure run back to what It's expected to be(290psi liquid line and 80psi suction)...
    Where does this come from? 68/250psi for a 407c dryer is more in line to what I've seen.

    What model unit? Does it have HGBP? With zero airflow and holding a 60psi suction, I suspect it has some sort of load control.

    With the air being dumped to atmosphere in your test, rather than storage tank, maybe it's at a lower temp so less load?

    I may have already said too much for open forum. Consider ringing tech support if stuck. None of us like to, but sometimes it's for the best.

  7. #7
    Join Date
    Oct 2019
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    Thread Starter
    Unit Novia model 1125. I'm sorry for my confusion as I said it use TXV but it's not a TXV it's HGB. And as suspected to the loading problem I looked at compressed air machines guage (temperature, pressure of compressed air are no different with the one that still can running fine at other places). I also have full diagram of this system but didn't see major difference, it don't even has control board just run through 220v direct to fan and compressor all the rest of loading is control by HGB.

  8. #8
    Join Date
    Nov 2011
    Location
    East Side
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    the first thing I do to air dryers having problems is clean the coils. they may not look bad, but they usually are dirty.

    Is your hot gas bypass bleeding through when it shouldn't be? or running when it should not be?

    since you've adjusted charge, I would pull the refrigerant, then weigh in the factory charge to eliminate it as a problem.

  9. #9
    Join Date
    Oct 2019
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    Thread Starter
    The condenser is cleaned and subcool is really really high even if I block liquid line to HGB valve because I think it's over feeding. But the result is still the same: high subcool, high pressure, high suction just within 1 hour or so the pressure switch will cut-off. I do properly charge it with rate KG labeled on the machine. It over pressure only if connected to storage tank. Don't know what is the cause yet.

  10. #10
    Join Date
    Nov 2011
    Location
    East Side
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    Did you change the TXV?

  11. #11
    Join Date
    Oct 2019
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    Thread Starter
    Yes I do swap it with a good one. But it's still not working.

  12. #12
    Join Date
    Oct 2019
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    Thread Starter
    Quote Originally Posted by 71CHOPS View Post
    Did you change the TXV?
    Forgot to mention that it not TXV it's HGB and it use capillary tube instead.

  13. #13
    Join Date
    Jul 2012
    Location
    WA
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    How much superheat when the pressures are high, where are you measuring it? Just to confirm, you have verified that hot gas bypass is not raising the suction pressure...if so, how have you verified it?

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