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  1. #27
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    Aug 2006
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    Mixing oil and fire with a big spoon.
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    Quote Originally Posted by 71CHOPS View Post
    Some RTU manufacturers are using the digital inputs for fixed speed operation. Say stage one would be 30hz and stage two would be 60 hz. No modulation based on duct static, etc.

    So it’s possible....
    Interesting and ridiculous. A 2 speed motor and 2 contractors are cheaper, use less energy and is simpler in operation.

    As for this motor, we still haven’t heard what the line-to-line voltages are. They are likely ok but you never know. Also, it is probably just a case of an oversized motor moving too much air.
    "Right" is not the same as "Wise".

    Don't step on my favorite part of the Constitution just to point out your favorite part.

  2. #28
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    Sep 2018
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Restricted air flow reduces amp draw!

    Is this a 2 speed motor?
    Operating off of contactors or a speed drive?
    Usually, but you would have to see this ductwork. The other technician cut the return ductwork open just to test this out and also noted the amp draw decreased.
    It's a seriously poor job done on the installers part. Like a bear hugging the returns and short runs at that.

  3. #29
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    Sep 2018
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    Florida
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    Thread Starter
    Quote Originally Posted by thatguy View Post
    I missed the part about the VFD. If it’s not the mixed up wiring then you may need to go into the parameters of the VFD setup menu and change the Current Limiting setpoint to meet the motors specs (if that particular function is available with that VFD).


    Sent from my iPhone using Tapatalk
    That was done.

  4. #30
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    Sep 2018
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    Florida
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    Thread Starter
    Quote Originally Posted by heatingman View Post
    You need to slow down the blower.

    Carrier wants this done via the pulleys, as they expect high speed to run 60 hrz.

    You can change the programmed speeds aswell, but that requires an interface for the drive that they likely did not give you.

    Open the drive pulley to get the amperage in range for the motor. Or replace the pulley with a smaller if need be.

    Also, Im suspicious of the fuse block and or its connections. Its pretty rare for the fuses on a drive to blow unless theres a real problem like a short, as the drive will act as overload for the motor.


    Sent from my iPhone using Tapatalk
    Check all connections and they were fine. Every piece aside from the fuses are factory. I recommended changing the fuse holder as it has seen some damage already. There are two RTU packaged units right next to each other experiencing the same issue, blower motor fuses overheating due to high draw and shutting down. The return ductwork is (4) 18" round flex, apx. 10' in length being sqeezed together around a corner and through cutout cinder block.
    I have ways reduce the amp draw, but would like to hold off until the ductwork is redone.

  5. #31
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    Oct 2009
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    Atlanta,Ga.
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    If you have poor return air, your amp draw goes down.you are moving less air.When you adjust the fan sheave larger, you move more air, your amp draw goes up.not sure what your problem is,But not drawing less return air.sounds like a possible problem with the VFD.you may be moving too much air on second stage, try adjusting fan sheave ,if all electrical looks good.

  6. #32
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    Sep 2018
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    Florida
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    Thread Starter
    Quote Originally Posted by Gleng View Post
    If you have poor return air, your amp draw goes down.you are moving less air.When you adjust the fan sheave larger, you move more air, your amp draw goes up.not sure what your problem is,But not drawing less return air.sounds like a possible problem with the VFD.you may be moving too much air on second stage, try adjusting fan sheave ,if all electrical looks good.
    If it is moving too much air in second stage and we know the return is undersized and too restricted-- it does make sense to fix that issue first before messing with the RPMS, right? It does after all have a VFD.
    Also, lowering return air is not universal for increasing amp draw. Depends on several factors. The opposite is true for PSC motors for example.

  7. #33
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    Aug 2002
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    Quote Originally Posted by Goldwaves View Post
    If it is moving too much air in second stage and we know the return is undersized and too restricted-- it does make sense to fix that issue first before messing with the RPMS, right? It does after all have a VFD.
    Also, lowering return air is not universal for increasing amp draw. Depends on several factors. The opposite is true for PSC motors for example.
    B S

  8. #34
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    Oct 2009
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    Atlanta,Ga.
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    you are correct.Fix return air issues. I would think there are also other problems here.like low suction, coil freezing ,low superheat..may wash out the compressor oil .now there is a bad compressor.Might be ok on first stage.Ductwork is large enough.On second stage, trouble is just around the corner.You are correct.Get ductwork and airflow fixed.you can only move so much air thru restricted ductwork.you can increase the fan so much, before the motor is over amped.this will help ,but the proper thing is to have the proper ductwork .Adjust your motor to the correct amp draw.All other things will fall in place.

  9. #35
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    Sep 2018
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    Florida
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    Thread Starter
    Quote Originally Posted by pecmsg View Post
    B S
    You can check this out for yourself, a lot of residential units still have a PSC motor. If you decrease return air, amp draw will also decrease.

    Now on a VS motor it depends more so on capacity.

    However there are other factors that determine what will happen: motor type, direct drive or belt, enclosure, variable speed, fan blade/type, motor HP, duct size, type of ductwork, RPMs, seizing, loose bearings... The list is ridiculous.

    Lowering return air is not universal to increased amp draw!

  10. #36
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    Nov 2006
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    Most RTUs use a squirrel cage blower. If you take off the blower access panel while the unit is running, you increase airflow into the blower, and current rises due to the increased load.

    If you block the return with a fire damper (don't ask how I know that) the current runs low and the airflow stalls in the wheel, becoming chaotic.
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  11. #37
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    Mar 2008
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    Quote Originally Posted by timebuilder View Post
    Most RTUs use a squirrel cage blower. If you take off the blower access panel while the unit is running, you increase airflow into the blower, and current rises due to the increased load.

    If you block the return with a fire damper (don't ask how I know that) the current runs low and the airflow stalls in the wheel, becoming chaotic.
    Honeywell you can buy better but you cant pay more

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  12. #38
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    Jan 2010
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    Quote Originally Posted by crazzycajun View Post
    X2

  13. #39
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    Jul 2012
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    WA
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    What type of blower wheel does this unit have? Is the VFD set at fixed speeds, or is it modulating? How is a motor drawing 25 amps blowing a 30 amp fuse? What’s the max current setting in the VFD?

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