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  1. #14
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    Aug 2013
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    Quote Originally Posted by Coldtech67 View Post
    Exactly the way I see it too, thanks.
    To answer your other question about sight glass not being full with a fan cycle this is normal operation generally...

    What you are seeing is the liquid actually boil (flashing) in the liquid line due to the sudden drop in head pressure.
    If there's no check valve between the receiver and condenser here's what will happen.
    Startup...glass clears very quick, both pressures buildup and unit begins to cool
    Once the head pressure gets to the fan cycle cut in, the fan comes on. Normal operation continues but head pressure falls due to low ambient, etc...glass is full still.

    Now...as the head pressure falls, the glass will bubble (due to the rapid drop in head pressure). Head continues to fall until the fan cycle switch opens and the fan stops.
    From what I've learned...this is the key part.
    If they are charged up adequately, then as soon as the head pressure starts rising the glass will clear rapidly again.
    Thats how fan cycle systems work, especially if theres no check valve.
    Headmaster systems are a much better choice

    Sent from my SM-N920V using Tapatalk

  2. #15
    Join Date
    Mar 2015
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    Medford, N.Y.
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    OP. What is the meaning of the term "slugging a comp"??? A part of the definition of the term "slugging" involves "little or no SH measurement".... An undercharged unit usually has high SH.

    But I think that a system w/o a proper head press control will lead into a slug getting back to the comp due to the lower press going into the metering device which causes very little
    "proper atomization" of the freon which leads into low mass flow problems which leads into oil/freon flow problems which leads into slugging, I think.

  3. Likes Blake79 liked this post
  4. #16
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    Feb 2010
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    montreal
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    Quote Originally Posted by Coldtech67 View Post
    I was told that if the ambient temp gets too low and there is no fan cycle control the compressor can be slugged. From my understanding no fan cycle, head of coarse drops, subcooling too high, sight-glass not full, system will operate as undercharged. Am I right?
    If you run a system with too low head pressure this will affect your low pressure (it will drop) as low pressure drop saturated temp will drop.
    If it's a rooftop ice will form, restrict air flow and you might at some point slug the compressor.

  5. #17
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    Sep 2002
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    Virginia
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    Only time ive ever witnessed sluggin is an overcharge , or if someone had the txv too far open.

    If you take a condensing unit made for indoor use (no head master / fan cycle ) and put outdoors in winter, yes it will appear undercharged on cold days having SG look like a lazy river , but its not going to slug liquid back...theres not enough head pressure to cause a flood

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  7. #18
    Join Date
    Sep 2002
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    Virginia
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    Quote Originally Posted by HVAC_Marc View Post

    I run my non-fan controlled AC unit when it's 19F out.
    why.....

  8. #19
    Join Date
    Jan 2010
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    Quote Originally Posted by Snapperhead View Post
    why.....
    Because it's a heat pump as well....

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  10. #20
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    Mar 2013
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    Billington Heights, NY
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    Quote Originally Posted by Snapperhead View Post
    why.....
    because it gets hot in here?

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  12. #21
    Join Date
    May 2003
    Location
    Utah
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    Pressure drop across the TEV port has a direct bearing on TEV capacity. The lower the pressure drop, the lower the capacity. So, a minimum head pressure is required to maintain minimum pressure drop across the TEV port, to maintain the TEV capacity at the minimum level to meet the load demand.

    Lower than normal pressure drop across the TEV will result in high superheat, due to the reduced refrigerant mass flow as the result of the reduced pressure drop across the TEV port. At this reduced mass flow condition, the suction riser will be oversized, potentially causing oil to log in the evaporator. At some point, when there’s enough oil logging to result in an increased pressure drop in the evaporator, it will cause a slug of oil to come back to the compressor.

    Slugging is different than floodback (zero superheat).

  13. Likes icemeister, BALloyd, 2sac liked this post
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