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  1. #27
    I just wanted to thank everyone for their well reasoned responses to my question.

    Just for the record, I checked both the ambient temperature ( ground level shade) and the temperature of the air entering the condensor of my current rooftop unit.

    The ambient temperature was 108F and the temperature at the condersor(half way up) was 125F.

    By the way, I encouraged all three HVAC contractors to join this site and read this thread.

    Thank you again for your time and consideration.


  2. #28
    Join Date
    Apr 2004
    Posts
    7,680
    Thanks for the response Delta, but in my testing of thermocoupled motors, run time doesnt increase the motor temperature. I would say motors were born to run not cycle. That said, any unit running in a residential application of cooling had propbably better not be cycling when its 110 degrees outside anyway. It should run all day. We might need to consult an engineer but from what little I know, Carrier used to maintain that the start of a compressor is equal to 4 hours run time in wear. In other words, cycling is much worse than running. Contacts dont butn when closed, they burn when closing and opening. I just dont think increased run times (as abstract as it is) will cause equipment to fail sooner.

    As far as copper goes, I myself have never witnessed a case where normal refrigerant has worn out the copper by flowing through it. I'm only one guy so I have little to go on. It might happen but I dont think it happens very often. Yes refrigerant is a solvent but again, unless it is acidic I dont see it wearing the coper out. Even when it is, and I remember seeing compressors with copper plating as a result, I dont recall it ever actually wearing the copper out. Add moisture and yes it might just. Cycling, stops and starts flow which has to be harder on the copper.

    Hoses. hoses are most often used in a static application. You and I run all kinds of crap through them when recovering refrigerant. We also subject them to the air and vacuums on a regular basis. hoses do eventually become porus (sp?). And I think technicians should replace them regularly anway. I pretty much changed them at the most every 18 months but usually annually. I also worked with as many as 5 different refrigerants as a refrigeration technician. Vacuum's were important, especially on lower temp stuff, and I found older hoses just didnt do the job. Often I resorted to copper tubing with flare nuts to assure a good vacuum.




  3. #29
    Join Date
    Apr 2002
    Location
    Ann Arbor, MI
    Posts
    2,986
    Originally posted by Irascible
    I don't recall if critical temperature is eased into or just a sudden event.
    It is simply a point on the P-H diagram... on the very top of the dome actually. It is the highest temperature and pressure you can be at and still remain saturated. Your P-T card cannot list values above this point.

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