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  1. #1
    Join Date
    May 2006
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    Carrier Motormaster

    Hello,

    I had posted the below in the controls forum which is probably the wrong location. Hopefully this is the correct forum.

    We are looking at adding a Motormaster Head Pressure Control to our carrier unit. I've done some searching and see that there's Motormaster I, II, III and V versions. Has anyone installed one of these? We have two condenser fan's that we would like to control via VFD \ pressure - so I'm "assuming" it would be version V.

    Thanks

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    Do you want to control both fans with one VFD? If so the VFD must be rated for amp draw of both fans.

    I would think the Carrier Motormaster install literature should have specs in it for which one might be best fit for your unit.

    This sounds like something crazy no-brainer to say, but since Aaon did it, it bears mentioning: be sure there are no motor contactors between the VFD output and the motors once you install the VFD. Hopefully Carrier isn't as silly when it comes to condenser fans and VFDs as Aaon has been.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  3. #3
    Join Date
    Oct 2011
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    Chicagoland Area
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    Never had luck with motormasters. Try a T775 and a HW Smart VFD with a pressure transducer
    Officially, Down for the count

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  4. #4
    Join Date
    May 2006
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    Thread Starter

    Pressure Sensor

    Quote Originally Posted by 2sac View Post
    Never had luck with motormasters. Try a T775 and a HW Smart VFD with a pressure transducer

    Thanks for the feedback. Based on what I've read and posts, we will do this without the motormaster V. With that, what pressure sensor would you use for this? We already have a Johnson controls system and will be using ABB drives.

    Thanks for any insight

  5. #5
    Join Date
    Nov 2011
    Location
    East Side
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    How big are the fan motors?

    Just get a Couple is JCI P66’s.

    I’ve never been a fan of controlling head pressure off of temp. The interior line temp changes faster than the exterior, which causes a lag.

  6. #6
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    See if a Kele P51 is compatible with your JCI controls
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  7. #7
    Join Date
    May 2004
    Location
    SE Pennsylvania
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    If you are installing a VFD there is really no need for additional controllers. Connect a transducer with the proper range and a 0-10VDC output to the VFD and set up an internal PID to control the pressure. The JCI P499 pressure transducer kits come with a long harness and plug much like the Carrier transducers. If there are multiple circuits sharing condensers I am not sure how you would connect a transducer per circuit to the same VFD and control using maximum pressure within the VFD though.

    I have used JCI VFD66s for multiple shared circuited units before. They are designed to have two inputs but use an very specific transducer which I think is slide wire proportional.

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