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  1. #1

    Another AC won't cool below 80F Problem

    I live in AZ and one of my Goodman 3.5 ton SEER 12 units (only 2-year-old) is having trouble cooling the rooms below 80F in daytime after running for at least 3 hours straight (outside temp 100 to 110F). Using a laser thermometer, the temp coming out of the vents varies from 64F to 69F. My attic has R30 insulation. I've just changed the filter, and cleaned the condenser coils outside my house.

    When the tech came, here are some measurements he took:

    Sub cool: 11F / 10F
    Superheat: 5F / 5F
    Low side PSI: 75 / 77
    High Side PSI: 280 / 260
    Compressor: 22.1 - 18.3
    Condenser: 1.6 -1.1

    He told me those numbers look fine, and all he did is changing the piston from size 74 to 78 (according to him this will increase freon flow), and 'flush' the system.

    Anyway, those didn't help at all, and now I have to call them back and do more diagnostics. What else can I ask them to look into (besides duct leaks)?

  2. #2
    Join Date
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    A load calculation....that system might not be big enough to handle what you want it to do. 80 degree indoor with 110 outdoor is a large difference.
    If everything was always done "by the book"....the book would never change.

  3. #3
    Join Date
    Sep 2002
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    Did the system ever cool better than it does right now?

    Measure the temperature drop accross the air handler; if it's significantly greater than what you're getting at the vents, you could have a leaky return air duct or sections without (duct) insulation.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  4. #4
    Join Date
    Jul 2008
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    If your room temp is 80 (return air) and the supply air temp is 69 that is only an 11 degree TD, if the unit was operating normally it would be closer to 20 degrees. Its time for somebody else to look at it.

  5. #5
    Join Date
    Jan 2004
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    Hope he still has the old piston.
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    How many times must one fix something before it is fixed?

  6. #6
    Join Date
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    Western NC
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    Superheat of 5
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  7. #7
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    happens with dirty ID coils.
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    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Oct 2005
    Location
    phoenix az
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    Hmmm! I flush a toilet or flush a radiator but changing a piston to flush an A/C
    "Do not let what you can't do interfere with what you can do"

    "Do what you can do the best that it can be done and no one will ever know what you can't do"

  9. #9
    Join Date
    Mar 2005
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    Quote Originally Posted by skorepeo View Post
    Hmmm! I flush a toilet or flush a radiator but changing a piston to flush an A/C

    yea didnt you know it all goes down hill from there

  10. #10
    Quote Originally Posted by skorepeo View Post
    Hmmm! I flush a toilet or flush a radiator but changing a piston to flush an A/C
    Sorry, perhaps I shouldn't use the word 'flush'. According to the work detail, it's a 'System Evac', which he told me if something is blocking the line, doing that might help 'unblock' it.

    I went outside and check on my condenser unit, I see water droplets forming on the cold line running into the condenser unit, is this normal?

  11. #11
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    Quote Originally Posted by johndoe74 View Post
    Sorry, perhaps I shouldn't use the word 'flush'. According to the work detail, it's a 'System Evac', which he told me if something is blocking the line, doing that might help 'unblock' it.

    I went outside and check on my condenser unit, I see water droplets forming on the cold line running into the condenser unit, is this normal?
    Condensation is normal but you still need to have the system serviced and diagnosed properly.

    Believe us when we say cheap is not the route to take when it comes to HVAC.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  12. #12
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    Quote Originally Posted by iraqveteran View Post
    Superheat of 5
    According to my Goodman/Janitrol charging chart, with an outdoor Dry Bulb temperature of 110 degrees and indoor dry bulb of 80 degrees, with a piston metering device, suction superheat should be 0 degrees. But you don't want to add charge to a unit running at 5 degrees superheat or less. Instead wait till it cools off outside and charge to proper superheat at the new conditions.

    I would think checking for proper air flow and sealed ducts would be the next step. Doing a load calculation would not hurt either.
    Remember, Air Conditioning begins with AIR.

  13. #13
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    Quote Originally Posted by Kevin O'Neill View Post
    According to my Goodman/Janitrol charging chart, with an outdoor Dry Bulb temperature of 110 degrees and indoor dry bulb of 80 degrees, with a piston metering device, suction superheat should be 0 degrees. But you don't want to add charge to a unit running at 5 degrees superheat or less. Instead wait till it cools off outside and charge to proper superheat at the new conditions.

    I would think checking for proper air flow and sealed ducts would be the next step. Doing a load calculation would not hurt either.
    Checking for proper airflow is the FIRST step. Pressures should not even be taken until airflow is where its supposed to be. Cause without proper airflow, never gonna get good refrigerant charge readings.

    The technician is obviously a part changer and not a troubleshooter. Lets try this and see what happens......no thats not it either, now lets try this.....


    I can't stand part changers. Take your damn time and troubleshoot a system for once. 6 hours spend in one trip is a hell of a lot better than 6 trips at 2 hours each. What happened to taking your time? Everyone seems to be in a rush nowadays. Why? Your only moving backward when moving too fast. The tech needs to slow down and take the time to find the problem.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

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