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  1. #14
    Join Date
    Apr 2013
    Location
    Warren, OH
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    14
    And, one other thing that you said. Just to make sure I understood you correctly. On fan cycle control units, you still charge using the 90-30-1 chart?

  2. #15
    Join Date
    Jun 2007
    Location
    Williamsport, PA
    Posts
    176
    Quote Originally Posted by EricDMKAJ View Post
    You know, I've read this sporland document all day, and it finally clicked. You have to evacuate system completely of refrigerant before starting this process. Then, you figure out the volume of condenser. Then, you weigh in refrigerant until glass clears. You subract the number you just added from your total, and that's the additional you have to add in. Correct? Thank you so much, I am a tech that fully believes in the science side of the trade, and hate charging based on WAG. Thank you. You're a life saver
    You do not have to remove all the refrigerant to charge to the sporlan chart. Clear the sight glass first. Then add the refrigerant per the caculations from the chart to add refrigerant needed to operate in lowest expected ambiant.

  3. #16
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,924
    Keep reading, Eric.


    Let me try to sum it up for you.

    Let's assume an 80 degree ambient (for simplicity sake)

    Come up on a unit that is low on charge. Sightglass flashing hard.

    So, we find and fix the leak and start adding gas.

    Step one is to clear the sightglass. It doesn't matter how much or how little gas is in the unit to do this. Just add enough to clear the glass.

    Now, run Sporlan's numbers and reach your computed flooding charge and weight that charge into the unit.

    You're done.


    It gets more complicated charging them on a colder day, but let's get you straight on this, first.

  4. #17
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,924
    Quote Originally Posted by EricDMKAJ View Post
    And, one other thing that you said. Just to make sure I understood you correctly. On fan cycle control units, you still charge using the 90-30-1 chart?
    Most fan cycle units that I work on also have a headmaster.

    On those very few that don't, I'll add the computed flooding charge and go, too.

  5. #18
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Excellent. Ok, now I see what you're saying. Sorry for all the confusion, I'm just so used to refrigerators (critical charge) and central air, which I just charge by sub cool for Txv, and superheat for fixed orifice.

    So, as far as charging on a cold day, how is that done differently?

    As far as the lowest possible ambient, should I assume based on the area that I work, or is that stated on the condensing unit.

    And lastly, I was taught that if a unit has a receiver, I can't check sub cooling. And if it has an accumulator, I can't check total superheat at the compressor. True? Or not true.

    Thank you so very much for helping me through this. Going to the new job, they know my knowledge level is residential, and are training me accordingly. I just want to be prepared with the basics before I get knees deep in it

  6. #19
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,924
    Quote Originally Posted by EricDMKAJ View Post
    Excellent. Ok, now I see what you're saying. Sorry for all the confusion, I'm just so used to refrigerators (critical charge) and central air, which I just charge by sub cool for Txv, and superheat for fixed orifice.

    So, as far as charging on a cold day, how is that done differently?

    As far as the lowest possible ambient, should I assume based on the area that I work, or is that stated on the condensing unit.

    And lastly, I was taught that if a unit has a receiver, I can't check sub cooling. And if it has an accumulator, I can't check total superheat at the compressor. True? Or not true.

    Thank you so very much for helping me through this. Going to the new job, they know my knowledge level is residential, and are training me accordingly. I just want to be prepared with the basics before I get knees deep in it
    How is it charged differently? READ the document. It is rather difficult to explain, but the authors at Sporlan did a good job.

    Basically, you calculate the total flooding charge for a warm day, THEN calculate how much the condenser is ALREADY flooded due to the lower ambient, then add the difference.

    The minimum ambient is for the area that you work. I use -20 around here because, well, it happens every few years.

    You CAN check subcooling on a receiver system, it just isn't a good charging metric. Just as you CAN check superheat on a system with an accumulator.


    No problem on the assist. We all have to start learning somewhere.

  7. #20
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Excellent. Ok, I'm going to try to soak this document in as much as possible. I'll get it to stick, haha. Thanks again.

    Going back to the accumulator, your evap superheat shouldn't change, but total superheat should, is how I understand it. I would assume accumulators used on cap tube or orifice split AC?

  8. #21
    Join Date
    Sep 2008
    Location
    Western PA
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    25,924
    Quote Originally Posted by EricDMKAJ View Post
    Excellent. Ok, I'm going to try to soak this document in as much as possible. I'll get it to stick, haha. Thanks again.

    Going back to the accumulator, your evap superheat shouldn't change, but total superheat should, is how I understand it. I would assume accumulators used on cap tube or orifice split AC?
    Why would an accumulator change superheat?

    Does it add heat? Remove it?

  9. #22
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Well, if its there in case of liquid making it back to compressor, I would think that the liquid boiling off could throw things off. I could be way off with this, I never deal with them on centrals

  10. #23
    Join Date
    Jun 2012
    Location
    Tenn
    Posts
    139
    Quote Originally Posted by EricDMKAJ View Post
    Excellent. Ok, now I see what you're saying. Sorry for all the confusion, I'm just so used to refrigerators (critical charge) and central air, which I just charge by sub cool for Txv, and superheat for fixed orifice.

    So, as far as charging on a cold day, how is that done differently?

    As far as the lowest possible ambient, should I assume based on the area that I work, or is that stated on the condensing unit.

    And lastly, I was taught that if a unit has a receiver, I can't check sub cooling. And if it has an accumulator, I can't check total superheat at the compressor. True? Or not true.

    Thank you so very much for helping me through this. Going to the new job, they know my knowledge level is residential, and are training me accordingly. I just want to be prepared with the basics before I get knees deep in it

    Ice machines and small critically charged systems have only one method of assuring a proper charge. Sure walk ins and large reach ins can often be charged using the variety of methods, but those smaller critical charged units are so tight, that I have found recovering all refrigerant and charging the system by weight is the only way to assure a proper charge. I'll also say that before putting a gage on anything like that, I will make sure I don't have an electrical problem, which is far more common than a refrigerant charge issue. Unless you already got some, may I recommend that you get a couple short hoses with a valve and put a suction gage on one and a discharge gage on another? You'll want to use gages that retard on very high pressure, as nothing frustrates me more than an ice machine going into harvest while I have a suction gage attached to it that can't handle the high pressure. The long hoses on our regular gage and hose set remove enough refrigerant to make a difference if you apply the gages a few times. The shorter hoses with a gage really come in handy for me, if I do need to check the suction or discharge pressures. Good luck, however with your new career line. Personally, I prefer refrigeration and ice machines than AC's, though I still have to work on AC's.

  11. #24
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,924
    Quote Originally Posted by EricDMKAJ View Post
    Well, if its there in case of liquid making it back to compressor, I would think that the liquid boiling off could throw things off. I could be way off with this, I never deal with them on centrals

    Not really.

    Think about it.

    If liquid is coming back the suction line, you already have 0 degrees superheat.

    The accumulator catches it and allows it to boil off slowly.

    How would this raise or lower the superheat?

  12. #25
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    So, what you're saying is that it's possible to check super heat at evaporator, obviously. But, checking it after the accumulator is not gonna give you a necessarily accurate reading. It will vary based on the amount that boils off. So, lets say you hoped to achieve a super heat of 20 or so without an accumulator, then you would expect a lower number with one? I'm beginning to think that I'm over thinking some of this stuff, haha. Trying to get too technical

  13. #26
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    And Bobbycold, thanks for the advice. Never thought of the shorter hoses on smaller systems. Makes total sense

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