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  1. #1
    Join Date
    Jul 2013
    Location
    Richmond, VA
    Posts
    1,751
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    Digital guage dilemma

    I went to go replace a leaky Comfortmaker evaporator coil today. Nice sunny day, 75 degrees this morning, coil was located in a cape cod type attic, so everything was set to be perfect. In a little over an hour, I had a new filter drier on, the new coil in place, all my joints looked factory - as they always do. Only bad thing that's happened so far is I set off the smoke alarm and scared the poor lady. Oh well. I pressurize the system with nitrogen, check for leaks - none of course. Pull a vacuum and after 30 minutes, I'm down to 95 microns - I was REAL happy.

    So I go to open the service valves and start it up. Everything is purring along nicely - wait, what's this? 18 degrees subcooling? Hmm, let me run it a little longer.

    22 degrees subcooling? Now that pit in my stomach is growing. What did I do - did I damage the TXV, was nitrogen not flowing and I stopped up the strainer? Non-condensables maybe? Surely it'll clear up.

    25 degrees subcooling. GREAT! 3 hours and this job has been nothing but perfect, now I'm going to have to pull the charge and start all over!

    Wait - my LL temperature is 67 degrees? Surely that can't be right because it's at least 80 degrees out now. I take my clamp off the liquid line and my temperature keeps going down into the 50s. I put my stick thermometer on and I'm reading 10 degrees subcooling on the dot. So everything was just fine, except my clamp...


    This is what I hate about digital gauges.

  2. #2
    Join Date
    Jun 2007
    Location
    Bucks County, PA
    Posts
    164
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    Yea.....That could be a problem. Or when you do your A/C work dealing with 90% Magic Pak PATC type units, from Condos, Apts, student housing, 55+ communities...... Watching the look of the maintenance mans face is PRICELESS!!!!!!

  3. #3
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    20,995
    Post Likes
    Quote Originally Posted by CircusEnvy View Post
    I went to go replace a leaky Comfortmaker evaporator coil today. Nice sunny day, 75 degrees this morning, coil was located in a cape cod type attic, so everything was set to be perfect. In a little over an hour, I had a new filter drier on, the new coil in place, all my joints looked factory - as they always do. Only bad thing that's happened so far is I set off the smoke alarm and scared the poor lady. Oh well. I pressurize the system with nitrogen, check for leaks - none of course. Pull a vacuum and after 30 minutes, I'm down to 95 microns - I was REAL happy.

    So I go to open the service valves and start it up. Everything is purring along nicely - wait, what's this? 18 degrees subcooling? Hmm, let me run it a little longer.

    22 degrees subcooling? Now that pit in my stomach is growing. What did I do - did I damage the TXV, was nitrogen not flowing and I stopped up the strainer? Non-condensables maybe? Surely it'll clear up.

    25 degrees subcooling. GREAT! 3 hours and this job has been nothing but perfect, now I'm going to have to pull the charge and start all over!

    Wait - my LL temperature is 67 degrees? Surely that can't be right because it's at least 80 degrees out now. I take my clamp off the liquid line and my temperature keeps going down into the 50s. I put my stick thermometer on and I'm reading 10 degrees subcooling on the dot. So everything was just fine, except my clamp...


    This is what I hate about digital gauges.
    That has not happened with my digi cools....
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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