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Thread: Rebuilt - Repeat Problem

  1. #1
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    Rebuilt - Repeat Problem

    Ok, so I've finally recharged and started back with testing. The same problem has presented itself.

    When the sight glass was still bubbling, the liquid pressure was climbing above 300PSI, Suction pressure was 90PSI, superheat was high, and subcooling was low. Previous tests started with low liquid pressure and high suction pressure before the original problem when I first charged it up.

    Everything pointed to undercharge, except for the high liquid pressure. The low subcooling seems to suggest that it's not a restriction.

    I'm confused... I'm kinda thinking TXV or Solenoid Valve... I'm going to experiment later with a few ideas before I jump to conclusions, though.

    Any other thoughts?
    Last edited by Stewie007; 09-23-2016 at 07:31 PM.
    Regards, Stew.....

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  2. #2
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    In retrospect, it may have been wise to replace the TXV just to be safe... but I didn't... and so it goes...

    Liquid Pressure: 325PSI
    Suction Pressure: 70PSI
    Superheat: 8-10F

    I experimented with a little liquid injection by partly opening the ball valve between the liquid line and suction line. The resulting injection succeeded in keeping the liquid pressure stable, and helped to achieve a lower suction pressure. Though, it stabilized only at 70 PSI. The sight glass was clear at some points, but not at others.

    The Suction Pressure being where it is suggests that the charge is too low and the valve isn't acting properly to meter the refrigerant; that was what happened during the very first test on the first revision (the test that ended successfully).

    The discharge/liquid pressures suggest that there is too much charge, or the compressor isn't getting enough cooling. It also suggests that the TXV is defective, but I doubt that. The Solenoid valve could be plugged up as well. No detectable temperature change on either side, however. The TXV may alleviate some of that, though.

    I'm still confused, and also reluctant to keep adding charge until I have thought about it and talked it out.......

    Oh, and by the way... I evacuated the hell out of this system. Had a stable micron reading below 500 and all.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  3. #3
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    I thought about it....

    Time to recover refrigerant and check the TXV and Solenoid valves like I should have before... After thinking about why the liquid injection worked, that told me the evap wasn't getting enough refrigerant... Perhaps the receiver had some debris in it that gummed up the works and partially blocked the valve.

    So.... I hate to say it after all this time..... but it's gonna be a while. (Last semester at least.... LOL)
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  4. #4
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    Some bubbles in a sight glass is normal till it has reached homoeostasis.

    A filter dryer should all ways be befor the TXV as they can be easily blocked as can the solenoid!

    All so the compressor must be matched to the TXV at operating load! Too small of a TXV on too large a compressor will cause such symptoms as will too much air in the system, but I know your skill level is better then that but should point it out as we can all miss such things.
    Bring back natural selection! No more warning lables!

    The one and Only MG Pony

  5. #5
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    Always fine with people throwing ideas on the wall.

    I'm mostly disappointed that I didn't check the solenoid valve and decided to go ahead with the redesign and rebuild of the liquid line. As for the F/D I went with a flare connection on both the filter drier and the sight glass (Male Flare Drier, Female/Male SG) so I could connect them directly to each other with the sight glass after the drier and before the receiver.


    Fortunately, I think the liquid injection test has successfully isolated the problem to one of two valves.

    I'm going to fully replace the TXV most likely (the power head seemed to be fine), but I think I may determine if a motorized ball valve would be a better idea for the pump down. However, if there is an obstruction inside that solenoid valve, I could remedy it with a strainer for less $$.

    In the meantime, I'll get a service kit for the solenoid valve to replace the seals and any other fouled parts. Fortunately, I bought one of those R Series Parker valves that are easily disassembled. There isn't a lot of room to sweat connections on that part of the machine.

    At any rate... it won't be that tough of a job; I'm just glad I put that ball valve in the bypass line instead of a solenoid. It allowed me to test my hypothesis regarding the additional restriction since I proved that the original F/D was indeed clogged.

    Not only was the subcooling extreme past the drier back during the first test cycle, but the discharge superheat and temperature were equally ludicrous. It was far less pronounced this time, with pressures climbing in a much more delayed fashion. This restriction is apparently minor (Whew...)

    Hey, somebody warned me that all of this *expletive deleted* was going to be difficult to build, charge, and tune.... let alone test. I listened, but I was intent on proving that wrong. Well..... I failed... LOL.... While I will solve this issue, it sure has kicked me in the................

    Several warned me....
    Last edited by Stewie007; 09-12-2016 at 03:47 PM.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  6. #6
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    And FYI, I decided to make it official and buy a recovery machine and cylinder instead of borrowing.

    Borrowing has worked out in the past.... but I'd rather have ready access.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  7. #7
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    Ok. No thanks to Parker, I found myself a solenoid valve repair kit. I'm gonna crack the thing open and check for blockages, etc.

    I've also gotten a back-up TXV if that needs to be replaced as well. I reckon I can sell it if I don't need it for what I paid; shipping was the same price regardless.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  8. #8
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    Sorry folks, I was on my way to solving the problem until the company from which I've ordered the service kit and spare valve decided to put my order on hold due to an obsolete part number.

    That's fine, but they've been extremely unresponsive in follow up after that.... It's quote annoying...

    I could have gone with another company, but until now I haven't been in a big rush... If they don't respond by Wednesday, I'm cancelling my order and moving on.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

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