My Residental A/C Unit's low side pressure.
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  1. #1
    Join Date
    Jul 2008
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    4

    Confused My Residental A/C Unit's low side pressure.

    I have 2 Amana 1.5 ton Copeland Piston condensing units. One for 1st fl and 1 for 2nd fl. The 1stb floor low side is about 70psi @ 78F ambient and the unit is about 20ft level from the unit to the evap. They are both orifice units and I noticed this unit splits off after the orifice into 2 cap tubes but the whole evap does not seem to be sweating. Not sure if 1 cap tube is blocked?

    The upstairs unit (same model) is about 50ft run and about 25 ft straight up. They are about 9yrs old. I have always heard a surging sound running up the walls to the attic unit. It also runs and runs but does cool. Just seems to be slow. Could be undersized (Only 1.5 ton 900SF and a lot of sun) so after 9yrs I decided to throw a gauge on. The downstairs unit holds solid at a certain pressure.

    The upstairs unit fluctuates about every 3 mins from mid 50's psi to low 70's pgi. The needle is like a pendulum slowly going back and forth over about 3mins. I have a short video i took if you'd like to see it.

    So, is this normal for a install going directly up to swing in pressure like this? I am wondering if there could be some non-condensable in the system or maybe a low charge?

    I only work in refrigeration and I know if I have a low charge I am in deep vacuum and frozen evap.

    Any thoughts? Appreciate it.
    Last edited by jthomp7889; 07-26-2008 at 11:55 AM.

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    67,699
    Remove your email address, they are not allowed in post. You can put it in your bio.

    Would you consider that fluctuation normal on a refrigeration system?

    What would it mean if it was a WIC on the second floor with the condenser outside on the ground.
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  3. #3
    Join Date
    Jul 2008
    Location
    Coastal North Carolina
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    What superheat do you have on the suction line?

  4. #4
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    Jul 2006
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    Virginia
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    sounds like non codensables

  5. #5
    Join Date
    Jul 2008
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    Quote Originally Posted by beenthere View Post
    Remove your email address, they are not allowed in post. You can put it in your bio.

    Would you consider that fluctuation normal on a refrigeration system?

    What would it mean if it was a WIC on the second floor with the condenser outside on the ground.
    HI, I remove the email!

    These units have never been serviced so I am just getting into them. I probably won't replace until something big happens.

    Not sure what you mean by "WIC"?

    The low side fluctuation on a refrigeration system would not be normal. That's is why I am asking....

  6. #6
    Join Date
    Jul 2008
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    Quote Originally Posted by PDQuick View Post
    What superheat do you have on the suction line?
    I have not measured the superheat. The unit is in a tough tight location in the attic which also has no floor. I could measure the suction line temp before if enters the service valve at the condensing unit but not sure if that is effective....

    What would the superheat tell me? Not to sounds stupid but we never measure that in our business domestically.

  7. #7
    Join Date
    Jul 2008
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    4
    Quote Originally Posted by catmanacman View Post
    sounds like non codensables
    Have you seen this type of fluctuation before??? If there is NC in the system I am guessing they did not pull a good vacuum from the original install. If there was NC in the system I would see higher head pressures wouldn't I? I know there is not a lot of heat coming off the condenser. Not sure if that is normal or not?

  8. #8
    Join Date
    Mar 2004
    Location
    Illinois
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    6,959

    jthomp7889

    It sounds as if may be in the business, you need to read the requirements for becoming a pro member and apply. There are forums where your discussion can be but this forum is not one of them.

    The info being discussed here is better talked about in the private forums, sorry.

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