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  1. #1
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    674

    digi cool question

    i pumped down an a/c unit 2 ton rheem to leak check evap coil. factory test pressure 300 psig. ok so ill nitro it up to about 150-200psig. because im trying to hear this leak not sit around and look for a loss of pressure. anyways my low side flashes 123 psig and wont read any higher while on the r22 scale. so i figured maybe if i change my setting to r410a will read higher. nope the same pressure. then i took the hose of it went to 0psig i reconnect it and back to 123 psig flashing? i dont get it. it makes me think what if i was working on a 410a system where my back pressure is actually higher how does it know the difference or is it gonna flash 123 psig again,

  2. #2
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,467
    the limit on the low side transducer is 200psia. so once you get to ~ 185psig it will flash.

    because you read 123 it means you were really reading 223...There is no need to test that high.

    I test at 150 and hit hold. do some things and come back and hit hold again to see where im at.

  3. #3
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,918
    Quote Originally Posted by gravity View Post
    the limit on the low side transducer is 200psia. so once you get to ~ 185psig it will flash.

    because you read 123 it means you were really reading 223...There is no need to test that high.

    I test at 150 and hit hold. do some things and come back and hit hold again to see where im at.

  4. #4
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,706
    This seems to be one of those things that 'fools' us when we are using it.

    When I see the flashing low side... I just take it off and go back to zero. It always clears it and it works fine.

    I test around 175~ The point is to leave it for 5-10 min... With low side reading in 1/10 of a PSI... if it is gonna leak... it will drop 0.1 PSI within 5+ minutes. And as we know... there is always something we can button up or a tool we can retrieve (or put back) in the van.

    DigiCool is a cool leak testor after brazing up a system.
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  5. #5
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    674
    Quote Originally Posted by gravity View Post
    the limit on the low side transducer is 200psia. so once you get to ~ 185psig it will flash.

    because you read 123 it means you were really reading 223...There is no need to test that high.

    I test at 150 and hit hold. do some things and come back and hit hold again to see where im at.
    leaks that take 6 months plus to leak out if the leak is on the low side after an hour you might not see much of a pressure drop because r22 lo side pressure when the unit is off its more or less 120psig. depending on temp. but mainly if the factory tested the coil at 300psig im not doing anything wrong at 200 psig. i wouldnt go close up to it because yes the coil is older and make spring leaks all over.

  6. #6
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    674
    but how does it know its nitrogen in the system versus actually checking lo side psig on r410. it aggravates me why does it have to start flashing and sht. just say the actual pressure. i know its my fault for lack of knowledge with them,

  7. #7
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    674
    Quote Originally Posted by gravity View Post
    the limit on the low side transducer is 200psia. so once you get to ~ 185psig it will flash.

    because you read 123 it means you were really reading 223...There is no need to test that high.

    I test at 150 and hit hold. do some things and come back and hit hold again to see where im at.
    just curious what if you leave it at 150 and did nor press hold, can you just come back and see if it dropped? not arguing with your tecnique just trying to learn a better way to use them.

  8. #8
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,467
    yea you can. you just have to remember where you left it. if you it hold it will stay the same # but the bar graph still works and you can watch pressure drop.

    if you have 410a with low side above 200. you got high load or other problems to worry about

  9. #9
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,467
    200psi is 70* saturation temp. with 410a. your indoor coil shouldn't be that hot

  10. #10
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    674
    Quote Originally Posted by gravity View Post
    200psi is 70* saturation temp. with 410a. your indoor coil shouldn't be that hot
    im not referring to 410a operating pressures im talking about while the system is off your standing pressures. but about the 123psig why was it not reading higher what if i was working on a 410a system where the back pressures are about 135 psig. i know its can read higher because if i remember i used them for 410a several times with no issues but it does have me curious. or was it just a glitch or something but i hate when i dont figure something out.

  11. #11
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,467
    it is no glitch. if you get ~ 185psiG it will flash. if your at 199psiA i dont think it will flash

  12. #12
    Join Date
    Mar 2007
    Location
    wedged in freezer shelf
    Posts
    7,165
    I think with my 1250 the saturation temp gets locked as it is blinking but the psi keeps reading and goes up but you have to assume the hundredths value is a 2. Not sure how high it goes and still reads like that. For high pressure tests I just use the high side with a tee.
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    The low side should show you the actual pressure, down to the tenths of a PSI, all the way to 200 psi. It will start blinking when you get into a pressure range that is an abnormal operating range.
    Above 200 psi, it doesn't give you a good reading.

    If the low side just isn't reading pressure higher than 123 psi, it's broken.
    If more government is the answer, then it's a really stupid question.

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