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  1. #1
    Join Date
    May 2004
    Posts
    11

    Hmm

    I HAVE A PROBLUM WITH A NEW 5 TON SYSTEM GOING THROUGH COMPRESSORS DUE TO 29 DEGREE EVAPORATOR. I DID NOT INSTALL IT , JUST TRYING TO CURE PROBLUM. IT HAS A 20X40 RETURN AND PLEUM WITH EIGHT 8in. DROPS. STATIC PRESSURE AT RETURN IS .25, STASTIC AT SUPPLY IS .20. I CHECKED BLOWER SIZE, SPEED, AND ROTATION AND ALL CHECKS OKAY. IT USES A FLO-RATOR #82 AND AM RUNNING A 10 -12 SYSTEM SUPER HEAT. THE SUCTION LINE IS A LITTLE SMALL 3/4 INSTEAD OF 7/8 , BUT NOT ENOUGH TO CAUSE THIS. THE SUCTION LINE RUN IS ONLY 6FT. THE ONLY THING I DID NOT DO YET IS DISCONNECT THE BLOWER AND CHECK FOR FROST PATTERN ON EVAP. ANY IDEARS?

    [Edited by coldboy on 03-30-2005 at 06:18 PM]

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    Wait a minute? External static of 4.5"? Static on an air handler should be .3" with coil in it.


    8 8" drops seems light for a 5 ton. How is the supply?

  3. #3
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    Those static pressure readings can't be correct, at least not in inches of water. A standard blower in a residential unit could never generate those pressures under any conditions.

    What are the return and supply air temperatures?

    If your return air temperature is low, the 29 degree evaperator temperature could be normal.

    What is your subcooling?

    Make sure the orifice is the correct size listed for the outdoor unit. A #82 orifice seems small for a 5 ton system. That is a size I would expect to find in a 4 ton, or a high efficiency 3.5 ton system.


    [Edited by mark beiser on 03-30-2005 at 01:08 PM]
    If more government is the answer, then it's a really stupid question.

  4. #4
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Furnace or air handler??

    2.5 or .25 Static?

    If 2.5 tell us more about the duct sizes!!

  5. #5
    Join Date
    Apr 2004
    Posts
    7,680
    Go back and get tha ACTUAL airflow. The obttom line is you lack airflow, could be that the coil is already frozen.

  6. #6
    Join Date
    May 2004
    Posts
    11
    THE STATIC IS .25 AND IT HAS EIGHT DROPS THAT ARE ALL EIGHT INCH DROPS. THE RETURN IS 20X40 INCHES. SUBCOOLING IS 1 DEGREE.

    [Edited by coldboy on 03-30-2005 at 06:16 PM]

  7. #7
    Join Date
    Apr 2004
    Location
    Lubbock, Texas
    Posts
    267
    1 sq. ft of return per ton. what is the size of your supply duct? 8 8" drops @ 200 cfm each is 1600 cfm which is a little low but not bad but we still need to know if you are actually getting that to those drops either way it is an airflow problem and it sounds like you need to look at the supply before you seperate the blower wheel
    Learning never ends and everyone has something to teach. Some people teach me what to be like others teach me what not to be like!

  8. #8
    Join Date
    May 2004
    Posts
    11
    YA, BUT THE STATIC IS GOOD .25

  9. #9
    Join Date
    May 2001
    Location
    Abilene,texas
    Posts
    246
    HELLO ......... 1 deg of sub cooling ???? your low on gas period your coil is empty so either you have a discharge line restriction ( which i doubt) or your under charged but now lets be fair.... what is your superheat... if your at 25 or more add gas.
    Its not what you know its what you can prove.

  10. #10
    Join Date
    Apr 2002
    Posts
    11,808
    The return sounds starved.

    It also sounds like it is undercharged and under a low load.

    Low load as in a combination low air flow, and the return air is not all that warm or humid yet.



    [Edited by Carnak on 03-30-2005 at 11:18 PM]
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Originally posted by coldboy
    I HAVE A PROBLUM WITH A NEW 5 TON SYSTEM GOING THROUGH COMPRESSORS DUE TO 29 DEGREE EVAPORATOR. I DID NOT INSTALL IT , JUST TRYING TO CURE PROBLUM. IT HAS A 20X40 RETURN AND PLEUM WITH EIGHT 8in. DROPS. STATIC PRESSURE AT RETURN IS .25, STASTIC AT SUPPLY IS .20. I CHECKED BLOWER SIZE, SPEED, AND ROTATION AND ALL CHECKS OKAY. IT USES A FLO-RATOR #82 AND AM RUNNING A 10 -12 SYSTEM SUPER HEAT. THE SUCTION LINE IS A LITTLE SMALL 3/4 INSTEAD OF 7/8 , BUT NOT ENOUGH TO CAUSE THIS. THE SUCTION LINE RUN IS ONLY 6FT. THE ONLY THING I DID NOT DO YET IS DISCONNECT THE BLOWER AND CHECK FOR FROST PATTERN ON EVAP. ANY IDEARS?

    [Edited by coldboy on 03-30-2005 at 06:18 PM]
    You're measuring one degree of subcooling and between 10-12 superheat? What were the indoor and outdoor conditions (temperatures) like when you took these readings?

    How many compressors has this system eaten?

    What is your temperature drop across the indoor coil?

    Only thing I can figure at this late hour (and drooping eyes) is possible undercharge combined with poor airflow. Undercharge would explain low subcoooling and poor airflow would explain why superheat reads 10-12 vs. something a lot higher for an undercharge condition.

    How are you sure the other compressor(s) were lost from the symptoms you're seeing now? Could've been for a different reason and the last person that worked on it created a new set of problems with his repair methods.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Join Date
    Apr 2004
    Posts
    7,680
    Get the following information.

    Outdoor Air Temperature
    Indoor Air temperature
    Return Air temperature
    Supply Air Temperature
    Actual Airflow (right now we have .45" total static)We want actual airflow.
    Suction Pressure
    Head Pressure
    Suction line temperature at unit
    Suction line temperature at indoor coil
    Liquid Line temperature at unit
    Liquid Line temperature at indoor coil.
    Calculate Superheat at outdoor unit
    Caluclate Subcooling at outdoor unit.
    Measure liquid line leaving condenser.
    Provide Line size for Liquid Line
    Provide Line size for Suction line
    Provide Line set total length
    Provide the vertical seperation
    Is the indoor unit above or below the unit.

    Include Outdoor unit Model Number
    Include Indoor Air Handler Model Number
    Include Indoor Coil Model Number.

    Provide accurate info and we can tell you what's wrong.
    We'll figure out how to bill it later.

  13. #13
    Join Date
    Oct 2004
    Posts
    3,400
    Print this thread and go fill out Doc's questionaire.
    That will give something to go on.

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