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  1. #1
    Join Date
    Apr 2004
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    Testing for noncondensables

    You know the test... pump system down, disconnect compressor leads, power up the condenser fan and let it run until discharge air is same temp as entering air. Do a pressure/temperature comparison and if pressure is higher than the P/T chart says it should be, you have noncondensables.

    My question is, do you have to do the pump down? Not all condensing units have the internal access fitting, making it difficult and time consuming to perform this simple test. Can the test be done with refrigerant equalized throughout the entire system?
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
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  2. #2
    Join Date
    Jun 2006
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    No, to measure anything you need a reference point. Isolating the refrigerant outside and using the fan to stabilize the od temp of the coil to ambient gives you a reference point. With an 80degree OD temp and 70degree ID temp......who knows....
    Give a man a fish, he will eat for a day. Teach a man to fish, he will eat for a lifetime.

    Give a man a capacitor, doesn't know what to do. Teach a man to install it, now he knows everything.

  3. #3
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    Apr 2004
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    So, how does one check for noncondensables if the unit does not have the internal access in the condenser? I suppose you could recover the refrigerant into an empty cylinder, let the tank temp stabilize and do a P/T comparison on the tank. Or, recover the unit and add an access. Both methods are quite time consuming and therefore expensive. Is there a simpler way? Will a superheat and subcooling measurement point out noncondensables?
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
    Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii

  4. #4
    Join Date
    Nov 2004
    Location
    Austin, TX
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    876
    Sometimes a system without the necessary shutoff valves won't allow you to diagnose a problem inexpensively.
    Eliminate all other causes of high head pressure first before going with non-condenseables.



    http://www.achrnews.com/articles/che...oncondensables
    "Air can enter a refrigeration system in one of two ways. It can enter a system through poor service practices such as not purging refrigeration hoses while working on a system or not completely degassing a system after it has been open while replacing a component or repairing a leak.

    Air can also enter a system if a refrigerant leak has developed on the low side of the system and enough refrigerant escapes to cause the low side to run below atmospheric pressure. If refrigerant is then simply added to the system without addressing air pulled in, it will remain trapped in the system and cause future problems.

    If a service technician encounters a system running at elevated high-side pressures, one of the causes could be noncondensables trapped in the system. This is not a very common occurrence but it is possible.

    Before thinking that noncondensables are the cause of a system problem, a technician should look at the more common causes of elevated discharge pressures.

    Common causes of elevated high-side pressure on systems using an air-cooled condenser are dirty coils, insufficient airflow across the condenser, and recirculation of condenser air. These possibilities should be investigated first before looking at noncondensables as the cause."
    I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.
    ― Benjamin Franklin

  5. #5
    Join Date
    Jan 2010
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    6,263
    If you have narrowed it down to non condensables can you weld on a saddle type access fitting at the top on the condenser ? If so do that and bleed off your air.

  6. #6
    Join Date
    Apr 2004
    Location
    MN
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    Thanks for the replies. All good info.
    VTP99-I don't actually have a unit that I suspect contains non condensables. A question was asked in class today and I told them the pressure/temperature comparison method. Then, when we went in the lab, I was going to have them do the test and none of our A/C units have the internal access fitting in the condenser. Yes, we can install saddles on all the units. I was just wondering if there is any different test to prove non condensables are in the system. As mentioned in the article allan38 posted, ruling out all the other possibilities of high head sounds like the best way.
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
    Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii

  7. #7
    Join Date
    Sep 2007
    Location
    San Antonio, Tx
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    43
    Don't forget the filter driers, quick vacuum won't pull out moisture if the caps have been off awhile, use a micron gauge to be sure

  8. #8
    Join Date
    Feb 2013
    Location
    New Jersey before and after Texas
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    65
    If I suspected non condensable gases by doing the test you described, I would recover the hydrochlorofluorocarbons, pressurize to test tolerances of nameplate data, isolate the system into three parts (line set, condenser, evaporator), then pull a vacuum if there was no leak.. It would be a good idea to change the drier and compressor oil before weighing in a new charge with any proven methodology.

  9. #9
    Join Date
    Feb 2013
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    New Jersey before and after Texas
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    P.s. I keep saying hemoglobin in refrigerant lines would take iron to transport oxygen. Imagine a surfactant lined purge system for non condensable gases?

  10. #10
    Join Date
    Dec 2005
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    Cincinnati, Oh
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    Quote Originally Posted by Joseph'bidness View Post
    If I suspected non condensable gases by doing the test you described, I would recover the hydrochlorofluorocarbons, pressurize to test tolerances of nameplate data, isolate the system into three parts (line set, condenser, evaporator), then pull a vacuum if there was no leak.. It would be a good idea to change the drier and compressor oil before weighing in a new charge with any proven methodology.
    There's other ways for non-condensables to get into a system other than a leak.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  11. #11
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    Apr 2004
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    MN
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    Quote Originally Posted by Joseph'bidness View Post
    If I suspected non condensable gases by doing the test you described, I would recover the hydrochlorofluorocarbons, pressurize to test tolerances of nameplate data, isolate the system into three parts (line set, condenser, evaporator), then pull a vacuum if there was no leak.. It would be a good idea to change the drier and compressor oil before weighing in a new charge with any proven methodology.
    It's not always practical to change the oil. (hermetic compressors with no drain plugs)
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
    Gene Castagnetti-Director of the National Memorial Cemetery of the Pacific in Hawaii

  12. #12
    Join Date
    Jul 2009
    Location
    South Carolina
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    3,197
    I've been doing this for 30 years & have never found a way to test for non-condensables except by guessing with the system running.
    On heat pumps if you had moisture in the system it might take a while to run in heating before the metering device would plug up instead of blocking up immediately but the standing pressure test has never worked for me. Just too many variables. It's not like you're going to be dealing with 50% air & 50% refrigerant. Of course I've never used digital gauges either.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  13. #13
    Join Date
    Oct 2012
    Location
    Sacramento,ca
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    196
    Quote Originally Posted by garyed View Post
    I've been doing this for 30 years & have never found a way to test for non-condensables except by guessing with the system running.
    On heat pumps if you had moisture in the system it might take a while to run in heating before the metering device would plug up instead of blocking up immediately but the standing pressure test has never worked for me. Just too many variables. It's not like you're going to be dealing with 50% air & 50% refrigerant. Of course I've never used digital gauges either.
    X2. The only way i have ever used is paying very close attention the gauges and the sounds of the compressor. We have a local large company that didn't vacuum 1000's of systems just purged the lines with refer and called it good. The sound of non-cond as it cycles through the compressor is not hard to miss and the gauges will move quite a bit.

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