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  1. #1
    Join Date
    Sep 2011
    Posts
    85

    Semi-hermetic valves leaking?

    Saw a compressor short cycling twice a second. Found the low pressure control out of calibration, made it work, though i think it should be replaced.

    While setting the low pressure control (with my gauge on), i notice the pressure climbing from 10psig, to the 30psig in about 10 seconds.

    Is this the soldenoid valve or the compressor valves? if it's the compressor valves, how do i know if it's suction or discharge valves? (though i recognize that both should be replaced during a rebuild)

  2. #2
    Join Date
    Apr 2010
    Location
    San Diego, CA
    Posts
    204
    Easiest way to diagnose this one would be to take a look at that solenoid valve. It'll be cold on the outlet if it's leaking through that bad.

    I never bother trying to figure out ahead of time if its bad suction or bad discharge valves. If it's got bad valves, I'm going to be replacing the valve plate either way.

  3. #3
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    617
    Quote Originally Posted by wdshea View Post
    Saw a compressor short cycling twice a second. Found the low pressure control out of calibration, made it work, though i think it should be replaced.

    While setting the low pressure control (with my gauge on), i notice the pressure climbing from 10psig, to the 30psig in about 10 seconds.

    Is this the soldenoid valve or the compressor valves? if it's the compressor valves, how do i know if it's suction or discharge valves? (though i recognize that both should be replaced during a rebuild)
    sounds like its low refrigerant, or restriction and the compressor is cycling off due to the low pressure control setting. once the pressure rises to what ever the cut in setting/ high event is set to then the compressor will kick back on. does the pressures go from 10 psig up to 30 psig while its still running. or does the compressor shut off then the pressure rises up to 30psig??? more info would be good. did you get it going?

  4. #4
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,163
    turn off high side service valve while running , and when your low side drops to 5 psi , quickly turn off the power to compressor.

    This simulates the LL valve closing . If you see the suction begin to rise 10 - 30 like its been doing , then your valves are shot

  5. #5
    Join Date
    Mar 2008
    Location
    kansas
    Posts
    141
    I think what snapperhead meant was to shut off the liquid reciever valve to simulate the lls closing never shut off the high side on compressor when its runing very bad idea
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  6. #6
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,595
    What was the reason for you being there? Was there a problem or was this something you noticed? Low charge, llsv leaking by, long line set is me just thinking out loud.

  7. #7
    Join Date
    Sep 2011
    Posts
    85
    i was working on a line cooler that is in the same rack. there are about 10 refrigeration circuits on the rack.

    thanks for the service valve trick, i feel like a dumbass for not thinking of that myself.

    anthony, the compressor would pump down to 10psig (it was struggling to get from ~13 to 10 psig), then after the comp was off the pressure would slide back up to 30 and do it again. that would take ~10 seconds.

  8. #8
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,163
    yep , struggling to pump down is another sign the valves are leaking

  9. #9
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,595
    Quote Originally Posted by Snapperhead View Post
    yep , struggling to pump down is another sign the valves are leaking
    ^^^^^^

  10. #10
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    794
    Are you only watching it do this once or twice, or does it continue to do this on and on? Sometimes with long lineset or large evaps, it can take a couple of pumpdowns before the low side is clear of liquid refrigerant.

  11. #11
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Quote Originally Posted by crazzycajun View Post
    I think what snapperhead meant was to shut off the liquid reciever valve to simulate the lls closing never shut off the high side on compressor when its runing very bad idea
    Yes sir. You close the discharge service valve and start it the valves will difinately get junked. Just close the suction service valve. If it pull down comp valves good go to LLS. If it doesn't pull down and hold get a valve plate.

  12. #12
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,585
    Quote Originally Posted by MicahWes View Post
    Are you only watching it do this once or twice, or does it continue to do this on and on? Sometimes with long lineset or large evaps, it can take a couple of pumpdowns before the low side is clear of liquid refrigerant.
    This
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  13. #13
    Join Date
    Feb 2007
    Location
    Georgia
    Posts
    162
    While you have that valve plate off you want to check piston and bore for wear and damage, if it is air cooled (no oil pump) you will need to check the wrist pin too.

    When you drop a suction valve lots of time other damage will happen

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