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  1. #27
    Join Date
    Jun 2004
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    St Paul, minnesota
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    1,015
    Quote Originally Posted by pecmsg View Post
    ICM senses the line temperature. I’ve used them on smaller applications.

    The Penn P-66 Control operates on pressure and is designed for larger loads.
    p-66 needs a high temp ball bearing motor ($$$$)

  2. #28
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    first of all you need to set a high differential on the fan cycler

    then, if you have problems burning up the contacts

    have the fan controller operate a relay that controls the motor



    .

  3. #29
    Join Date
    Jan 2010
    Location
    New Orleans metro area
    Posts
    161
    Quote Originally Posted by crab master View Post
    Agreed with most of the statements you've gotten here; however the last transmitter site I worked on they were paranoid about dust. I had to write a sequence that the economizer would only run during the months snow was expected to be on the ground, Nov - April, basically my take was their guys didn't want to change filters. I was at a loss on why they didn't use economizers more than what they did cause they could've saved a lot on the electric bill.
    On the fan cycling controls the tech is definitely incorrect with the application you are running in. Scroll/Recip (conventional) compressors in this type of application will need head pressure control. IMO - on aircooled equipment anytime you are running cooling continuously less than 65 deg F outdoor air temp then you need some kind of low ambient/head pressure controls.
    I would definitely put in a ball bearing motor and I would go with the P-66 or ICM fan cycling control, whichever can handle the load the best based on motor HP.
    A fan cycling control would work as well, but given your conditions it will be cycling quite a bit. I've gone as far as putting in overated contactors for the fan and having the fan cycling simply cycle the low voltage to the contactor and let the contactor take the brunt of the abuse. The other thing I've found is all to often fan cycling controls get set too tight. Let the pressure climb for a bit before the fan kicks on and then make sure it can't run continously less than the min. pressure you want to see. This lengthens your fan run times a lot.
    I agree . on R22 systems we've set the penns to CI at 325 psi and CO at 225 and closely watched the suction pressure as to keep it from dropping below a 64 psi while in an on cycle as a base guideline. We set the penns to control the condenser fan relay / contactor control voltage exclusively.No problems to date as a result other than " good office samaritons occasionally reporting the units are short cycling". Yes ,you read it right .Good luck .

  4. #30
    Join Date
    Feb 2009
    Location
    Missouri
    Posts
    16
    Get a hoffman control that you can start the motor and run a more constant head rather than racing it up and letting it fall through the floor. Ball bearing motor is a must for the low rpm setups.

  5. #31
    Join Date
    Apr 2009
    Posts
    12
    A Carrier Motor Master is also a way of going depends how critical the application is. A ball bearing motor is also needed with it.

  6. #32
    Join Date
    Oct 2009
    Location
    Atlanta,Ga.
    Posts
    196
    Scroll or recip,is not the issue.Expansion valves do not operate properly with low head pressure and flash gas. Systems need proper head pressure and proper charge to operate properly whether they are reciprocating or scroll.

  7. #33
    Join Date
    Mar 2005
    Location
    N.J.
    Posts
    149
    controling head pressure is just part of the solution.In this situation I would also install a crank case heater and install pump down and posibly a hot gas bypass valve to insure compressor longevity.We have alot of jobs like yours with the same type of equipment that we modified with all the above and once we sold the customer on this initial investment, they claim thier compressor replacemens are way less then before.

  8. #34
    Join Date
    Oct 2007
    Location
    Richmond, VA
    Posts
    351
    Quote Originally Posted by maxpower View Post
    When your "next" guy comes out,have him install the modulating type of controller. ICM makes a good one. Switches wear out and their not consistant enough for head pressure/temp. control. Just my opinion.
    X2

  9. #35
    Join Date
    Dec 2006
    Location
    Middle Tennessee
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    Quote Originally Posted by tombeaux View Post
    I agree . on R22 systems we've set the penns to CI at 325 psi and CO at 225 and closely watched the suction pressure as to keep it from dropping below a 64 psi while in an on cycle as a base guideline. We set the penns to control the condenser fan relay / contactor control voltage exclusively.No problems to date as a result other than " good office samaritons occasionally reporting the units are short cycling". Yes ,you read it right .Good luck .

    i worry about overheating the compressor and oil at 300 psi and above

    i like to max my head pressure controllers out at 295

    i keep about a 75 psi differential

    with those settings, the suction pressure drops to around 60 psi for a short duration, it's not gonna freeze

    also we don't let our computer rooms go under 70 degrees

    "somehow" the IT guys listen to us on that subject



    .

  10. #36
    Join Date
    Mar 2005
    Location
    Pacific Time Zone
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    4,151
    Work in a -10 deg F day, you'll change your mind. Granted where you don't see the temperature swings as drastic you won't have to set it as far apart, but when your freezing up units because someone set the differential too low and the cut out at 200 (cut in at 250) and you watch your head pressure drop to 150 before it starts to climb...
    Not only that but just because you set it at 325 doesn't mean it's going to run there very long at all, especially on cooler days. Many 105 - 115 deg days where it does run that pressure most all day long and units still running for years. Units in my house - knock on wood, are 12 years old and they seen many days running over 300 psig.
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  11. #37
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    Dec 2006
    Location
    Middle Tennessee
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    Quote Originally Posted by crab master View Post
    Work in a -10 deg F day, you'll change your mind
    your right, at 10 below i would not worry about compressors overheating


    .

  12. #38
    Join Date
    Dec 2004
    Location
    Brooklyn, New York
    Posts
    170
    All good points about the P66 controller and associated head pressure controls. You can go for cheap-fan cycling control to expensive-put a drive on the condeser fan (also replace the motor with a drive compatible motor). As far as the switch on the neutral side, I ve been taught never on neutral of 115volt circuit. On 208/230volt there is no neutral as you stated, thats just expression. Back to the original thread at hand, you stated that the mechanic said no fan cycling control needed. This might be true- depending on your condensing unit. Do you have a liquid receiver? How about a head master valve? If you have that stuff you can run a condenser fan balls to the wall, while ur liquid gets fed to your txv at almost a constant temp/pressure. I believe that is how Liebert does that. Also that is how we set up our refrigeration condensing units to operate in the winter time.

  13. #39
    Join Date
    Mar 2010
    Location
    Sunny SoCal
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    2
    Quote Originally Posted by LightGuy48 View Post
    I'm kind of confused by the switch comments because there really is no neutral. Unless you're working on a 110v window type unit most of the time the fan windings are from phase to phase so it's going to have 208, 240, or 480v across it, no matter which side you put the switch on your still on a leg with voltage, not a neutral. I can't think of the last time I saw a unit with a neutral, only a safety ground.

    Maybe they're saying the 'neutral' leg implying it's the simpler side since it has no capacitor on that side to worry about, but it's not at neutral potential.

    Just for clarification as stated earlier, 277 has one hot & one neutral leg.



    Also wind influence (passing objectionable air past the condenser coil) should be considered/addressed when/where a factor of head pressure control.

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