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Thread: AAON Copeland 2 speed failure

  1. #1
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    AAON Copeland 2 speed failure

    I am on a site which has multiple AAON RTU cooling with gas heat ( 25 ton ) with Copeland " variable " speed tin can compressors . Many compressor failures . I am new to this particular site . Did I walk into a hornets nest or a previously neglected situation ? I have limited exposure to the COPELAND DIGITAL Compressor . Asking for info. I am a centrifugal mech by trade

  2. #2
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    Who diagnosed the compressor failures? Were they digital scrolls that failed??

    Digital scrolls could look like they are bad when they are not to those unfamiliar on how they operate.
    Quote Originally Posted by CHILLERSVCMAN View Post
    I am on a site which has multiple AAON RTU cooling with gas heat ( 25 ton ) with Copeland " variable " speed tin can compressors . Many compressor failures . I am new to this particular site . Did I walk into a hornets nest or a previously neglected situation ? I have limited exposure to the COPELAND DIGITAL Compressor . Asking for info. I am a centrifugal mech by trade
    Sent from my SM-N910W8 using Tapatalk

  3. #3
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    I have seen many maintance guys and techs diagnose a digital scroll as being bad because they dont know how they operate. They are very reliable compressors. They have a solenoid that opens and closes for capacity control using hot gas bypass. They sound weird and when unloaded the head pressure drops and the suction rises. What were the failures of the previous compressors?

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    They are digital scrolls ; confirmed model numbers . Confirmed electrical failures ; shorted to ground . I feel there maybe other problems with the refrigeration circuits also. There are several factory installed accessories on each RTU - Modulating Hot Gas Reheat Valve and condenser pressure fan cycling. Supply fans are on a vfd fixed @ 40% . I have just begun to obtain details . I was not certain how far Bldg manager wanted me to investigate. As of Friday I was given " green light " to proceed . These are constant volume units . It is a warehouse / distribution center . JCI control system is only supplying occ /unocc command and RTU point monitoring through a PT Link. Facility is 24 /7 . I also observed that a compressor was replaced in the past 30 days and liquid line filter drier is original and no suction filter installed ; reported to be an electrical failure.

  5. #5
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    What brand or type of controls been installed into the aaon unit.( mcs, Wattmaster or other)?

    Seem like a commissioning issue.
    System where started to fast without a good adjustment.
    You can start by validating air flow at evap.
    If have started a good share of aaon for our local rep and can say they are good unit.

    And yes if dryer original and no succion dryer as been installed on a burnout issue this might explain a lot (about the recent compressor failure and the way the company as been working as hvac tech.)

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  7. #6
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    Thread Starter
    The on board controls are ORION / WATTMASTER .

  8. #7
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    You will need to find what as been programmed in the control board.
    You either will need a tool to connect to the board or see if you have a interface on site
    Btw you won't be able to connect if pt link is connected at the same time
    http://www.wattmastercontrols.com/

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  10. #8
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    Bldg mgr has handed me VCM-X operator interface module ( on Friday ) with manual. ( THANKS for the heads up patpinet )

  11. #9
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    Aaons are built for the job/building/application they are installed on. So if you call tech support, they can tell you if the blower is suppose to be fixed at 40%, or if it should modulate with building demand.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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  13. #10
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    Quote Originally Posted by CHILLERSVCMAN View Post
    They are digital scrolls ; confirmed model numbers . Confirmed electrical failures ; shorted to ground . I feel there maybe other problems with the refrigeration circuits also. There are several factory installed accessories on each RTU - Modulating Hot Gas Reheat Valve and condenser pressure fan cycling. Supply fans are on a vfd fixed @ 40% . I have just begun to obtain details . I was not certain how far Bldg manager wanted me to investigate. As of Friday I was given " green light " to proceed . These are constant volume units . It is a warehouse / distribution center . JCI control system is only supplying occ /unocc command and RTU point monitoring through a PT Link. Facility is 24 /7 . I also observed that a compressor was replaced in the past 30 days and liquid line filter drier is original and no suction filter installed ; reported to be an electrical failure.
    In our HVAC shop I started a saying: "If it's an Aaon, it won't stay on".

    Multiple scrolls is how Aaon so often handles capacity control. I call it "whack-a-mole capacity control" as Aaon will stage on/off each comp as the load increases or decreases. The only modulation to be had is where the digital scrolls and/or hot gas bypass are used. In your case you have both, but of all of the scrolls there, how many are digital and how many have hot gas bypass?

    I have never seen hot gas bypass set up properly, either on a chiller that uses it or DX. These same systems invariably had oil return problems during low outdoor ambient operation. And multiple compressor failures. One memorable system was a 40 ton DX split system serving VAV boxes. The compressor was a Carlyle O6E with suction cutoff unloaders. During low ambient conditions it could only unload itself so far, and the condenser fan slow down to a point, that beyond those limits the hot gas bypass, not properly set up, was sorely needed. The system had suffered multiple compressor burnouts, all likely attributable to inadequate oil return, as that is what hot gas bypass is actually for, in addition to the common notion that it imposes a "false load" on the evaporator to keep it above freezing.

    Once the compressor was replaced I set up the hot gas bypass correctly, along with adjusting the unloader staging to better control the supply air temp, and for as long as I was still around to maintain that system it did not eat another compressor.

    Go to a class for the VCM-X controller if one is offered in your area (usually it's an Orion instructor who will run you through all of their controllers, but you can glean enough from it to learn the VCM-X). The class unlocked enough nuggets of knowledge I sorely needed to properly set up a couple of Aaon RTUs configured to run 100% outdoor air with energy transfer wheels.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

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  15. #11
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    Your best bet is to spend the day with the unit, learn the unit, clean the coils, see what its doen, take and document various measurements. Maybe chat with who did controls. Ect. Discharge line temp, ducting,


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