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  1. #14
    Join Date
    Feb 2012
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    Savannah, NY
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    82
    How would he know if it was a plugged or restricted cap tube? High low side pressure?

  2. #15
    Join Date
    Sep 2005
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    florida
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    5,512
    Quote Originally Posted by mwright View Post
    How would he know if it was a plugged or restricted cap tube? High low side pressure?
    Yep Low suction high head it's the same with a txv.
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  3. #16
    Join Date
    Oct 2008
    Posts
    784
    With that different tstat you installed, I'll bet f you can get your eyeballs on the evaporator coil, you'll see ice forming on just part of the evaporator where it's fed by the cap tube. Since you know your charge is right, you'd be witnessing the results of a restricted cap tube. Call Hussman for specified pressures and, while you're at it, the specified cap length & diameter.
    Also put that coil sensing tstat back on it after you replace the cap tube.


    "You never know what others don't know." -

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  4. #17
    Join Date
    Oct 2008
    Posts
    784
    Quote Originally Posted by HeinzHVACR View Post
    Same t-stat this is a fixed orfice so no expansion valve feeding all fans running clean evap clean condenser. i guess my question is why does this thing run on coil temp if there isnt an expansion valve why cant it run off box temp? I never understood that.
    Why coil sensing tstat? My guess is because it's an open faced. I take it that's another name for an air curtain cooler. Either way, there's outside air always coming in.

    Aside from walk-ins, I usually see R/I coolers (with doors) or sandwich/pizza prep tables coolers. The benefit I see for having a coil sensing tstat is it's nearly impossible to cause a freeze up of the evaporator coil. With a cabinet tstat, if a door is left open, it will remain in a cooling cycle endlessly, causing a freeze up. A frozen evaporator will further perpetuate that since airflow is blocked. The cabinet tstat would never be satisfied.


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  5. #18
    Join Date
    Feb 2012
    Location
    Savannah, NY
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    82
    Quote Originally Posted by crackertech View Post
    Yep Low suction high head it's the same with a txv.
    New to this.
    When you say high head do you mean high side pressure. Not familiar with the HVACR lingo.
    In other words are you saying low suction side pressure and high high side pressure is an indication of a restricted cap tube or TXV?
    Where are we getting the normal running pressures to compare to?

  6. #19
    Join Date
    Feb 2008
    Location
    California
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    2,066
    Quote Originally Posted by mwright View Post
    Where are we getting the normal running pressures to compare to?
    Raw experience! will tell you "normal pressure"

    But it may be more precise to use subcooling and superheat on a Cap tube to determine a restriction.

    High subcooling, High superheat.

    This means all of your refrigerant is sitting in your Condenser.

    Just checking pressures alone could be deceiving. If you're not feeding your evap coil with refrigerant and absorbing heat, you're not going to transfer that heat to the condenser either, which could leave you with low to normal head pressure, depending on how much refrigerant is crammed in the condenser. You could even have a high head pressure if you cram too much refrigerant in the condenser.

    Ever walk up to a unit with low suction, low head and think it's low on refrigerant...so you add refrigerant and still no cooling? all along it was a restricted cap tube

    Subcooling & Superheat are much more relevant than just a single pressure reading.

  7. #20
    Join Date
    Oct 2008
    Posts
    784
    Quote Originally Posted by Phase Loss View Post
    Raw experience! will tell you "normal pressure"

    Ever walk up to a unit with low suction, low head and think it's low on refrigerant...so you add refrigerant and still no cooling? all along it was a restricted cap tube
    reading.
    DITTO on the pressures. I hammered out a simular response, but computer went stupid.

    A low charge and a restricted cap tube can look identical on the gages. You've already elliminated the low charge part.

    As for what pressures are specified, call Hussman on Monday. That's what I'd do since designed suction pressures vary from one manufacturer to another based on the temp control and metering device used.


    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  8. #21
    Join Date
    Oct 2008
    Posts
    784
    Well now, MY malfunction rather than my computer's. Operator error. I found what I'd typed earlier:

    Quote Originally Posted by mwright View Post
    New to this.
    When you say high head do you mean high side pressure. Not familiar with the HVACR lingo.
    In other words are you saying low suction side pressure and high high side pressure is an indication of a restricted cap tube or TXV?
    Where are we getting the normal running pressures to compare to?
    Call Hussman with model/serno and ask them for what should be normal. That's what I always do. The designed suction pressures can vary from one manufacturer to another.

    Yes, with a proper charge, clean coil and functioning fans, a pressure reading that's too low on the suction side is very likely a restriction of the cap tube.

    Although high discharge pressure reading from specified can theoretically ALSO be a product of a restriction since there's no receiver (it's cap tube), I usually find that the head pressure will also be low. With a restriction being the brunt of the problem, heat load on system is far less and can show on the high side as lower pressure.

    A low charge (say, due to a leak) and a restricted metering device can look nearly identical on your pressure readings. However, you said you'd already weighed in a correct charge so have therefore elliminated a low charge as being your problem.


    "You never know what others don't know." -

    If I can't laugh at myself...then I'll laugh at YOU! -

  9. #22
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    Another possibility with an open face cooler is an airconditioning vent or door blowing the cold air out of the case.

    If all else fails, get some dry ice in a tub with some water and put it in the case then watch what happens with the vapour.

    If a draft is blowing the cold air out you'll see it.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

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