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  1. #1
    Join Date
    Dec 2005
    Posts
    3,953

    Confused

    Hey guys, It seems that half the techs I ask say taking the superheat is useful for systems with expansion valves, and half say its for capilary systems. And I seem to get the same split response about subcooling. I work mostly residential. Whats the right answer?

    Happy New year!
    Adam

  2. #2
    Join Date
    Apr 2005
    Location
    Australia : Queensland
    Posts
    797
    Originally posted by newoldtech
    Hey guys, It seems that half the techs I ask say taking the superheat is useful for systems with expansion valves, and half say its for capilary systems. And I seem to get the same split response about subcooling. I work mostly residential. Whats the right answer?

    Happy New year!
    Adam
    They are important in both systems , from my point of view anyway
    each system is mainly designed with subcooling , but to get the subcooling right you have to get the superheat right too.
    The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

  3. #3
    Join Date
    Oct 2004
    Posts
    3,400
    Originally posted by newoldtech
    Hey guys, It seems that half the techs I ask say taking the superheat is useful for systems with expansion valves, and half say its for capilary systems. And I seem to get the same split response about subcooling. I work mostly residential. Whats the right answer?

    Happy New year!
    Adam
    Taking the measurements is useful for any type of system, to identify trouble spots.

    However, when charging a TXV system, you charge by subcooling.

    And, when charging a cap-tube system, you charge by superheat.

    Both types can be charged by weight, if known.

    Trust, but verify.



  4. #4
    Join Date
    Feb 2004
    Location
    southern illinois
    Posts
    5,522
    i would say that there is benefit in taking both readings,no matter the metering device.

  5. #5
    Join Date
    Sep 2004
    Posts
    3,157
    Taking the measurements is useful for any type of system, to identify trouble spots.

    However, when charging a TXV system, you charge by subcooling.

    And, when charging a cap-tube system, you charge by superheat.

    Both types can be charged by weight, if known.


  6. #6
    Join Date
    Dec 2005
    Posts
    424
    With txv still want to check superheat depending on sytem working on around 5-15 degrees superheat. But subcooling is going to tell if you have refrigerant issue in system with a txv.
    Working residential units lennox has a different method to check they use subcooling on piston orfices to check there system charge. Most other units use superheat to adjust charge but i always check both so u know how the whole system is operating properly.

  7. #7
    in a nutshell.

    subcooling tells you how much refrigerant is in a system.
    most commercial systems 10 degrees subcooling tell you that the condenser has the proper amount of liquid refrigerant hence full charge.

    superheat tells you how much refrigerant is being boiled off in the evaporator coil. 2 degrees superheat = not much and could mean overcharge, dirty coils etc..,


  8. #8
    Join Date
    Sep 2005
    Location
    Texas
    Posts
    2,793

    Im amazed

    at the number of techs that NEVER check either one and how many dont even know what it is!!

  9. #9
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    Let's put it this way. If you are only going to take one measurement:

    For TEV systems, measure subcooling.

    For fixed restrictor systems, measure superheat.

  10. #10
    Join Date
    Jan 2006
    Location
    muncie Indiana
    Posts
    510
    Hey try this on for size.
    capped tube system.
    wet bulb temp @ mixed return air * 3 - 80 - outdoor ambient /2
    that is w/b * 3 -80 - odb / 2.
    ex. 62*3-80-90/2 = 8 degrees superheat.
    I got this formula off of this site over a year ago. It is as accurate as the manufacturers data plate stamped on the outdoor unit door. If you do have a txv metering system, you must charge by subcooling. You should always check both s/h & s/c on any system but you can expect 8-12 degrees superheat on a properly working txv system always. This is where your subcooling comes in. The more refrig. you add the more subcooling you will see.

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