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  1. #1
    Join Date
    Aug 2004
    Posts
    37

    Question

    Have you had a situation where there is 2 stages of cooling employing individual fans. Now, one fan spins clockwise, thus spinning the second stage fan counterclockwise due to the manipulation of the powered 1rst stage fan. Keep in mind that the 2nd stage fan is not powered but is spinning because of the first stage fan. Now when the 2nd stage is enacted, the spinning 2nd stage fan is powered and it spins the way that it was spinning from the manipulation of the 1rst stage fan. As a result the second stage bumps out on hi head due to lack of air flow. This is on of the most strangest things I've seen from a rooftop unit???

  2. #2
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,985
    Yes I have seen that.
    Usually somebody screwed up the wiring.

  3. #3
    Join Date
    Aug 2001
    Location
    Alberta, Canada
    Posts
    27
    I,ve experienced similar, but this "windmilling" effect usually spins the second stage fan blade backwards, causing a high load on start up, thus causing the internal overloads to open. Wind and turbulence from the first stage fan causes this. I haven't yet found the answer to this one.

  4. #4
    Join Date
    May 2004
    Posts
    12,275
    Originally posted by madarius
    Have you had a situation where there is 2 stages of cooling employing individual fans. Now, one fan spins clockwise, thus spinning the second stage fan counterclockwise due to the manipulation of the powered 1rst stage fan. Keep in mind that the 2nd stage fan is not powered but is spinning because of the first stage fan. Now when the 2nd stage is enacted, the spinning 2nd stage fan is powered and it spins the way that it was spinning from the manipulation of the 1rst stage fan. As a result the second stage bumps out on hi head due to lack of air flow. This is on of the most strangest things I've seen from a rooftop unit???
    Lennox does the same thing but uses an ambient sensor to operate the second fan.

    If your second fan is turning CCW and pulling air in then someone messed up. It must be a high torque start fan motor and must pull air out CW. If you run both at the same time you are screwed in cool outdoor ambient. I have run across fan cycle controls on the second cond motor.

    I don't like to re-engineer but, the engineer is not on the roof listening to my customer.

  5. #5
    There is a anti-windmill device sold by Young supply in the detroit area. I have ordered them many times and they work well.

  6. #6
    Join Date
    Aug 2001
    Location
    Alberta, Canada
    Posts
    27
    Compressed....I'm curious about this anti-windmill device. How does it work?

  7. #7
    Join Date
    Sep 2002
    Posts
    1,389

    madarius

    On three-phase units, usually the fans will overcome the backward rotation. In many cases single-phase won't even with a capacitor. In the past, in many cases we have installed a sheet metal splitter that seperates the two fans.

  8. #8
    Basically it attaches yo the motor shaft. It has a spring loaded hinged pin that sticks up and keeps the blade from going freespinning backwards. When the motor kicks on it blows down and is kept out of the way by the moving air. I havent had any problems with them kicking up and destroying the blades yet. They are cheap something like $20.00.

  9. #9
    Its made by a company ESP the vendor part# is aw12

  10. #10
    Join Date
    Jun 2004
    Location
    MidWest
    Posts
    64
    I have seen the same thing on the Trane Intelipacks. Compressed is right, those devices do work. I've used them a few times. I believe I used to get them through a carrier dist. called SCACD in So. Cal. when I lived there. That's good to know about Young's cause that's my prime dist.

  11. #11
    We've done exactly what twcpipes suggests, making seperate compartments for each fan. I wasn't aware of the anti-windmilling device. But I'll check it out.

  12. #12
    Join Date
    Jun 2004
    Location
    Richmond Virginia
    Posts
    1,078
    Your windmilling condenser fan motor probably has a bad capacitor. Most smaller equipment (even three phase) have PSC condenser fan motors. If the cap is bad, the motor will run in the direction it starts in. Therefore if it is windmilling backwards, it will run in that direction.

  13. #13
    Join Date
    Oct 2002
    Posts
    306
    try these from Johnstone supply

    S58-725 1/2" SHAFT
    S58-726 5/8" ""


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