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  1. #1
    Join Date
    Jun 2019
    Location
    Blue Bell PA
    Posts
    13
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    VFD's in rooftop units

    Just curious if anyone else has been having issues with VFD's installed in rooftop package systems on the blower motors?
    They are becoming more common and now I believe the Government has made them mandatory.

    I've been having some issues with them. Especially ICP units.

    I feel that the VFDs being located in the blower compartment is too harsh of an environment. I know its probably the best option. But I've had a few recently have issues.
    We all know that equipment owners don't always maintenance their units regularly. And I'm seeing the VFD's get affected by dirt. I even had a pizza shop that didnt change filters. The vfd had grease inside the heat sink!

    I actually bypassed a vfd once because it was having intermittent problems. But the motor seemed to only run at half speed without the vfd.

    Anyone else have any opinions about vfd's in rooftop package units?

  2. #2
    Join Date
    Jan 2010
    Posts
    17,333
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    Yep got a 1 year old Carrier popping fuses intermittently.

  3. #3
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,445
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    In my opinion a VFD located directly in the airstream is nuts.
    No man can be both ignorant and free.
    Thomas Jefferson

  4. #4
    Join Date
    Jun 2019
    Location
    Blue Bell PA
    Posts
    13
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    Thread Starter
    For whatever reason the motors won't run at Max Speed if if you bypass the vfd and wire line power straight to the motor. Does anyone know why that is?

  5. #5
    Join Date
    Jul 2018
    Location
    Wisconsin
    Posts
    983
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    VFDs can run the motor up past 60hz. I have a few running past 60hz.

    Sent from my SM-G960U using Tapatalk

  6. #6
    Join Date
    Jul 2018
    Location
    Wisconsin
    Posts
    983
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    This was okay with tech support. I think there sales/engineer f-ed up. I needed more supply static. The fan curve allowed it. I ran it up till I hit FLA. been running for a few years. Bearings haven't blown up yet..........

    Sent from my SM-G960U using Tapatalk

  7. #7
    Join Date
    Jun 2019
    Location
    Blue Bell PA
    Posts
    13
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    Thread Starter
    Thanks guys. Thats great info!

  8. #8
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,445
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    On bypass the motor should run at 60Hz.
    No man can be both ignorant and free.
    Thomas Jefferson

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