set and find differential???
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  1. #1
    Join Date
    Aug 2003
    Posts
    30

    Hmm

    setting a low pressure switch. i find different techs setting differentials crazy ways.
    refrigerant type 404a
    find your temp you want 35f
    the range you want to have cut in at 40f convert to 85psig
    cut out at 30f convert to 70psig
    now subtract the two pressures and there is your differential. 15psig
    does this sound correct?

  2. #2
    Join Date
    Dec 2004
    Location
    Broken Bow, OK
    Posts
    12
    Probably not. To begin with, ask yourself the question, "what temperature is the pressure corresponding to?" Box temp? wrong. Refrigerant temp? Aha! Then, as far as cut out temperature in concerned, ask "what refrigerant temp do I need to achieve Box temp". That depends. What are you cooling? Fresh flowers, or packaged meat? It makes a world of difference. My guess is that with a cut out temperature of 30 degrees, you might be dealing with window A/C temps, and not product refrigeration. I hate using "rules of thumb", but try Product temp minus 15-20 degrees = refrigerant off temp. Experiment with your own equipment, not a customers, though.

  3. #3
    Join Date
    Aug 2003
    Posts
    30

    Hmm

    makes no sence according to pt chart cut in, cut out.

  4. #4
    Join Date
    Dec 2004
    Location
    Yuba City, CA.
    Posts
    254
    I have found that if possible add a pump down solenoid and penn stat. Pressure controls can be a real headache. A stat is usually an easier way to contol temp.
    I will enter His gates with thanksgiving in my heart.

  5. #5
    Join Date
    Aug 2003
    Posts
    30
    it is always good for safetymeasures.

  6. #6
    Join Date
    Mar 2004
    Location
    St. Louis
    Posts
    6

    Talking

    that does not sound right.what you think don?

  7. #7
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Cut in and cutout need to be set to the evaporator temperature, not the box temp.

    This means that you need to know the delta t of the system.

    I get the impression that you're confusing the PT relationship somewhere along the line.

  8. #8
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Originally posted by lennoxman
    I have found that if possible add a pump down solenoid and penn stat. Pressure controls can be a real headache. A stat is usually an easier way to contol temp.
    Thermostats are much better than Penn stats, and work in all states, including those SOUTH of the Mason-Dixon line. True story.

  9. #9
    Join Date
    Dec 2004
    Location
    Yuba City, CA.
    Posts
    254

    Talking

    Yeah I get it. Not a phillips screw driver or a crescent wrench. It's a cross head screw driver and ajustable wrench. Thanks.
    I will enter His gates with thanksgiving in my heart.

  10. #10
    Join Date
    Dec 2004
    Location
    Yuba City, CA.
    Posts
    254
    I gotta give props to the old timers. It seems like they had to learn how to really work on things. Older refrigeration really kicks my butt.
    I will enter His gates with thanksgiving in my heart.

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