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  1. #14
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,148
    Yep you can prove this to him.. Take a SH reading on a system in the shop, then cover some of the condenser to drive the discharge pressure up and watch your SH drop.

    But as mentioned indoor temp and wet bulb has a lot to do with it to.

  2. #15
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    2,030
    Quote Originally Posted by ryan1088 View Post
    Make sure you report back how the teacher reacts when you tell him he's wrong and prove it....
    Lol i will think about it. Ive called him out before on the subject of testing voltage drop and DC 3 phase motors . He is a good teacher, not as technically sound as my last but has plenty of knowledge that i dont. If i do call him on it ill be sure to let you know.

  3. #16
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,337
    I'm just dying to ask about his thoughts on votage drop and DC motors....
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  4. #17
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    2,030
    Lol testing voltage drop across a wire/ switch ect. I belieave the specific exapmle in the book was a sequencer our instructor explained to us that an open circuit across the sequencer would show 0 volts on the meter despite what the books answer. So i argued it a little bit in class, went home and test his theory on a switch. The next day in lab ( off to the side) i proved the book accurate on a sequencer. ECM motors , books description was a brushless three phase, DC motor . Our instructor explained to us the book was written in 2007 and ECMs were now widely available in single phase. I had watched some youtube videos on ECMs with the same description the book had and pointed that out to him. He was not overly thank full. Im not complaining he doesnt claim to be a technical guru his background is mainly sheetmetal but, can you see why calling him out on this would not benefit anybody. And no this was not who instructed on flame rectification

  5. #18
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,337
    Well, it is good to see that you are able to check what he is telling you.

    Measuring voltage across an open switch WILL give you source voltage, and although fed by a single phase power setup, the common ECM motors have three phases (or winding groups), and use pulses of DC created from the single phase feed, by the electronics in the end of the motor.

    http://energyexperts.org/energysolut...l.aspx?id=3196
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  6. #19
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    2,030
    Yea thats exactly what i told him

  7. #20
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,144
    Higher head pushes more refrigerant through the fixed metering device, so the evaporate will flood which will mean that more liquid is in the coil and will boil off closer to the end of the coil, hence a lower superheat. Superheat is added heat after the refrigerant boils off, so the earlier it boils off in the coil the more superheat and the later the less superheat.

    Look at an A/C charging chart-on the 95 degree temps you will find a 5 degree superheat and at a 80 degree outdoor temp it will be more like 18 degrees or so.
    Now on a hot pull down you will have a high superheat at any outdoor temp until the box stabalizes.
    So yeah, the book is right. Hats off to instructors, but never take an instructors word over the book. Just sayin'. But also don't call the instructor out on it. Take from him what you can and move on without question.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

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