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Thread: unloaders

  1. #1
    hi everyone... this is my first post...i'm a student studying hvac at lincoln technical institute here in nj. while doing a web search i was happy to stumble across this website. i'm looking forward to gaining additional knowledge from experienced members here on this board. i hope everyone will remain patient with me and hope that my questions don't seem too simplistic.

    at this moment i'm interested in learning more about reciprocating compressor unloader operation and troubleshooting. can anyone help me out with this subject? is there a good online resource that addresses the subject in detail?

    thanks in advance...

  2. #2
    Join Date
    Apr 2005
    Welcome, you can learn alot here from guys here. What kind of semi compressors are you working on? Compressors can unload with oil pressure electric actuated or oil pressure operated on suction pressure or unload mechanical with electric solenoids.

    Might help if you study one compressor and how it unloads and move on. Let me know and I could hook you up with information

  3. #3
    Hi ej... and thank you for responding so quickly to my post... well right off the bat i've already learned from YOU, that there are at least 3 different types of semi hermetic unloaders designs... this is great! right now i'm not working with any of the 3, this is all independent study i'm doing on my own. i agree with you that it makes great sense to study one system at a time and move from there. i trust your judgement completely and will leave it upto you on where i should start. i should add that i may have a good chance to go to work as an apprentice for the Trane Company here in new jersey once school is complete. will some of the information you share cover trane compressors too? again... thank you so much for your quick attention... i hope one day i can return this favor some how.

    peace2U ej!

  4. #4
    Join Date
    Apr 2005
    I hope things work out at Trane, we need all the self motivated techs we can get. You could email me from my profile and I can send you information on Trane compressors models E,R,M

  5. #5
    Join Date
    Aug 2006
    Mixing oil and fire with a big spoon.

    unloaders can be tricky sometimes because some manufacturers use "loaders". i usually define the difference as: loaders, when energized, load up the compressors, and unloaders, when energized, unload the compressor. most information only refers to them as unloaders, though.

    Trane compressor models: K, M, R are unloaded when energized (unloaders)

    Models: A, B, E, F are loaded when energized (loaders)

    Copeland models are unloaded when energized

    these are when using the electric solenoid coil style

    there are a lot of really smart guys around here so feel free to talk to them!
    "By Grapthars Hammer....what a savings." Galaxy Quest

  6. #6
    Join Date
    Sep 2004
    Kansas City, Kansas, United States


    don,t forget hot gas unloaders like on a carlyle 06e.
    maybe you are looking for a simple answer like; a 12 cylinder compressor running fully loaded and the suction pressure gets down to 55 lbs, will unload one head so now the machine is only a 10 cylindeer then an 8 and so on then as the suction pressure gets up to 75 lbs it will load back up. really a pretty simple concept. good luck with TRANE great career move

  7. #7
    Join Date
    Sep 2004


    O6D &E had several styles, some electric pilot operated hot gas by pass, some suction pressure determines it. dumps discharged hot gas back into suction ports of same cylinder, when in ops the under side of head and compresor is warm to hot, when loaded it cold, suction pipe cold, easy to tell, to adjust low pressure trip for ops one turns the large top to adjust spring pressure, memory says all in is 75 psi all out is 55 ish, but i could have it reversed,, half heimzers today

    the difference to reset is under small cap adjuster on bottom mounting flange of capacity control.

    latter models E series went to suction cut off therby reducing out put via cutting intake, difference in head, has blank off looking plate on underside of head, is auctual, cut off valve insertion point, these can still be controlled via pressure regulated or electricl pilot oper. suction and hi side pressur operated system, old style doesnt bolt up to new style if you have to use newer replacement style, you may have to buy new unloaders, to get all the parts needed to make it work
    If you cant cool it
    HEAT THE Hello out of it

  8. #8
    Join Date
    Sep 2006
    For Semi-Hermetic Compressors Modulation or Capacity Control have couple of ways to control capacity. An example is to keep the compressor running and reduce its pumping capacity or amount of heat removed per hour. The process is called capacity modulation and the most popular method is referred to as unloading.
    These are the following:

    External Bypass Valve positioned on the head of the compressor for unloading high temperature applications. It provides a capacity reduction of about 35% and a power reduction of 20% from fully loaded operating conditions.
    Tandem compressors operation provides simple capacity reduction and maximum power savings because each compressor can run either simultaneously or individually.
    Blocked suction unloading uses an internal device to shut off the flow of refrigerant to a bank of cylinders in the compressor and reduces its capacity.
    Moduload allows compressed gas to fill a storage chamber above each compressor cylinder. This compressed gas then re-expands back into the cylinder during the suction stroke, reducing compressor capacity.

  9. #9
    Join Date
    Sep 2006
    lincoln is a great school youll learn a lot , keep your eyes and ears open

  10. #10
    Join Date
    Jul 2000

    Here is a PDF document on compressors from Trane.
    It has some inforamtion on unloaders of several styles of Trane compressors.

    And here is a document for Carrier 5H compressors that shows what the unloader mechanism is all about.,h-23si.pdf

    I suggest you save it to your computer and look at it at your leisure. One is 124 pages and the other is 40 pages.

    [Edited by wolfdog on 09-15-2006 at 03:54 PM]

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