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Thread: hoofbeat

  1. #1
    Join Date
    May 2008
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    Hey guys! explain to me please what is happening in a system, with condenser fan cycling control, when fan is not on sight glass fills but when fan comes on it empties to about 1/2 glass. Can the system be that low on charge? Cools fine, but then fan cycles on and the glass is about 1/2 empty again. Whats happening here? I have seen it on A/C R-22, on coolers with R-409A, freezers with HP-80 ect. ect. The only common factor is condenser fan cycling control. I have checked sub cooling at these conditions and everyone has had very low subcooling and adding charge brings it back to around 9 or 10 but still sometimes getting bubbles. All systems have reciever and TXV too.Except A/C R-22 has no reciever on it. Thanks

  2. #2
    Join Date
    Mar 2008
    North Queensland, Australia
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    When the fan cycles on the head pressure drops. the liquid backs up in the condenser. The supply of liquid to the receiver drops off and the system can drain the receiver till the head comes back up.
    you might want to increase the setting on the fan cycling control or add a bit of gas to the system. Or you could just put up with it if it's just flashing a bit.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  3. #3
    Join Date
    Jul 2008
    South Shore,Long Island
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    C. Ambient Fan Cycle Control
    This is an automatic winter control method which will maintain a
    condensing pressure within reasonable limits by cycling fan motors
    in response to outside air temperature. The thermostat(s) should be
    field adjusted to shut off the fan when the condensing temperature
    is reduced to approximately 90˚F. Table 7 lists approximate settings
    for several system T.D.’s. These settings are approximate as they
    do not take into account variations in load.

    CAUTION: Under no circumstance should all
    condenser motors be allowed to cycle
    off on one control. At least one motor
    shall be wired to operate at all times.
    Under most circumstances, the
    condenser motor nearest the inlet
    header should remain on whenever the
    compressor is operating.
    Design Thermostat Settings
    Models T.D. T1 T2 T3
    30 60
    2-fan units: 25 65
    20 70
    4-fan units: 15 75
    30 60 40
    3-fan units: 25 65 55
    20 70 60
    6-fan units: 15 75 65
    30 60 50 30
    8-fan units: 25 65 55 40
    20 70 65 50
    15 75 70 60

  4. #4
    Join Date
    Mar 2008
    Banana Republic,Florida
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    i'am having the same problem with a rack thats 3months old cant keep a full sight glass
    r-22 i have tryed different set-ups and setpoints and am always flashing i have 2-3 balls in my reciever my A-8 valve has been set every which way cant get a full column of liquid am still working on this problem i think the piping coming from my condenser is 2 5/8 it goes through my reciever comes out 2 1/8 i think thats my problem have you checked to see if you have a p.s.i drop any where?

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