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  1. #1
    Join Date
    Feb 2007
    Location
    Napa
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    111

    Sticking unloader

    I have a Copeland Discus compressor with a single unloader. The problem is that it sticks from time to time when loading or unloading, sometimes for several seconds. Should I be concerned about this? It is electric by the way...

    Thanks...

  2. #2
    Join Date
    May 2007
    Posts
    141

    Sticky unloader

    Should you be concerned, YES. It will mosty likely fail. Resolve the problem before it becomes a problem. Before making a mechanical repair be sure the signal is clear to the solenoid. An old analog meter is best (in my opinion) for this type of test. Attach it right at the solenoid connections and cycle the unloader signal, if voltage is not the problem, then you can either R/R the unloader, or remove it and inspect it for dirt, debris, etc., cylinder head ports will also need checking. Check the armature and how it may slide inside of the tube, and the spring. Any issues R/R it. You get the idea, you may need to get deeper into it if these items don't clear up the issue. Not knowing what type of equipment this compressor is on, or in, does not really make a difference. You know there is a malfunction, so troubleshoot it, and resolve it. Good luck.

  3. #3
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,349
    depending on model (number of heads) and how many unloading valve plates you have, you may be able to add an unloader to one of the other heads and stop using this unloader. many times, when you have a "6D..." model, it had 3 heads. only one is required to be a full load bank of pistons. you may only have 1 unloader, but one of the other heads may have the unloader valve plate but have a shipping gasket on it. if it is a 2 head compressor, you will have to repair/replace the unloader.
    "Mother" is the name for God on the lips and hearts of children....The Crow

  4. #4
    Join Date
    Feb 2007
    Location
    Napa
    Posts
    111
    It is a single head compressor.

  5. #5
    Join Date
    Feb 2007
    Location
    Napa
    Posts
    111
    OK...time for an update and a plea for help...

    This unit is an Energy Labs boxcar unit that is used for comfort cooling for a clean room.

    I have 2 compressors on this unit and they are both doing the same thing. The #2 compressor is smaller, but they both have the single head on the top.

    The compressor loads when coil is de-energized, so coil voltage can not be the problem, although I did install a new coil and top unloader valve. I pulled the top plate which exposes what I assume are the valves (there are 3 of them). There isn't anything obvious there.

    Emerson customer supports insists that there is nothing wrong with the compressor and/or unloader assy. They are trying to say that it must be the pressure switch not allowing enough time for the unloader to seat.

    I disagree with this as well, as none of the other compressor in my other units need this time in between states for the unloader to seat. Also, on this problem child, it doesn't matter how long the compressor is running unloaded. When the valve de-energizes to load the compressor, the unloader chatters for 30 seconds or longer. It does eventually seat.

    I am not sure how the discharge pressure plays into the loading of the compressor, but when running unloaded with minimal load on the compressor and mild ambient temps, the discharge pressures are about 160 psig.

    There is a hot gas bypass for the first compressor, but have not checked operations of that yet.

    My next question is...does it hurt these compressors to run for extended periods of time in an unloaded state? The way these units stage is first compressor unloaded, second compressosr unloaded, first compressor loads, and second compressor loads as fourth stage. It is not very often that this unit is running both compressors fully loaded.

    The DX coils are not stacked, so I was thinking it might be better to use first compressor as first and second stage and second compressor as third and fourth.

  6. #6
    Join Date
    Sep 2006
    Location
    Southern California
    Posts
    86
    So you took off head & looked at the under part of the head and the unloader assembly looked fine? those Unloaders are pilot operated so there are orifices that may clog up on u. The question of running at a unloaded state for long periods, I would say in theory it's not so great for oil return because of less suction velocity, although i have an account w/ 11 50BJ carrier units 6 steps of unloading per unit w/ no oil switches w/ no problems. I would recommend installing if not already installed a oil failure switch as a precaution.

  7. #7
    Join Date
    Jun 2004
    Posts
    182
    Elvis, you're dealing with a 3D compressor of some sort. As far as the compressor is concerned long unloaded times is not an issue. However like stated by Toy oil return needs to be watched during long periods of unloading.

    The chattering you're hearing is normal, but should only last for 1 to 1 seconds. It takes discharge pressure to force the unloader plungers down. What I suspect here is your head pressure as compared to the suction pressure may low. (?) You need to keep at least a 70 lb pressure differential between suction and discharge to load the plungers, if not, the plunger will chatter loadly.

    If the chattering is lasting for 30 seconds then you are not getting sufficient pressure differtial to the plungers. Maybe a restriction through the ports or bleed by the unloader plunger. Make sure you don't see any debris in the plunger cyclinder when you push down on the unloader plungers.


    You can remove the upper plate, this will let you see the top of the unloader plungers. Take a hammer handle and push down on each of the plungers to see if they are free to move up and down (don't hit them). There is a 70 lb spring under them so it will take some force but they should be smooth.

    Concentrate on why the pressure is not getting to the top of the plungers or why it is leaking by.

  8. #8
    Join Date
    Jun 2004
    Posts
    182
    Also you need the correct valve plate for the refrigerant in use. Please post compressor model number and the refrigerant. There is a valve plate for HFC's and a valve plate for CFC's/HCFC's.

  9. #9
    Join Date
    Feb 2007
    Location
    Napa
    Posts
    111
    OK...will post compressor model later today if I get a chance...

    The 3 unloaders can be pushed in with fingers and there does not appear to be any debris on or around the unloaders.

    Differential pressure is greater than 70 pounds...50-55/150-160 psig during operation.

    May have to check into the c/fan control to increase head pressure.

    Copeland oil safety installed on both compressors...

    Will be working on them today, will update...

    Thanks

  10. #10
    Join Date
    Feb 2007
    Location
    Napa
    Posts
    111
    Sorry for the delay in the update...VERY BUSY!!!

    Anyway, replaced unloader assy on both compressors and problem has been resolved...

    Just a note...I blocked the c/coil to increase head pressure to see if problem would go away since so many people that I talked to thought that the head pressure may have been too low, but that did not help...

    Thanks all for the input!!

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