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  1. #14
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    Jul 2004
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    Poughkeepsie, Ny
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    631
    Originally posted by beenthere
    You can't do the math, if you don't know how cold the outdoor design temp is, plus wind.

    Are you sure youo read 64, on the LL temp.
    The reading can't be right, if the OD is 85.
    What software do you use?
    I used my termomiter right inside the king valve. ( I used a CRT and inserted a termommeter)

    Those are the readings... That is why I am here asking questions. My guess would be that the system is overcharged, liquid is evaporating in the suc. line at the king valve giving me this temp. From what I understand is that the evap is supposed to be saturated 3/4 of it's volume in liq. and return gas back to the compressor. Correct? If I am getting liq. in my suc. line and lowering the temp, then I am saturating my compressor and my suc. line, which should ice up nicely on a cool day when they run the a/c. That is why I am cornfused.

    [Edited by atufano on 04-19-2005 at 11:40 PM]

  2. #15
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    Jan 2004
    Location
    Lancaster PA
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    You first said that 64 was the temp of the liquid line, now your saying suction line, that makes a big difference.

    That would be a superheat reading.
    At 55 wb, you have very low humidity. And shouldn't have much superheat. With out a pt chart in front of me, I think you have about 24, which would indicate, undercharge, or too high of an air flow.

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  3. #16
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    Jul 2004
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    Poughkeepsie, Ny
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    Originally posted by beenthere
    You first said that 64 was the temp of the liquid line, now your saying suction line, that makes a big difference.

    That would be a superheat reading.
    At 55 wb, you have very low humidity. And shouldn't have much superheat. With out a pt chart in front of me, I think you have about 24, which would indicate, undercharge, or too high of an air flow.

    Out @ Cond. 85 Dry
    In @ Return 55 Wet
    Suc line temp 64
    Lo 68 PSI
    High 190 PSI

    T-Stat reads 74

    If you are referring 24 to my superheat, the chart showed 4.
    I moved my wetbulb indicator to 56 and the dry bulb read "-" and the superheat read 4.

    As far as the air flow, we usually leave it on whatever the factory sets them for. Our Senior Tech does the estimates by sq/ft and bumps them up for a margin of whatever, I don't know and I don't think he does either.

    This is a 3 ton unit in a 1080 sq/ft house. There are 7-7" runs and 1-6" run. A 14" return. This was stubbed in by the builder 6 months ago. Which if you add up the supply's, it comes close to 1100 sq/ft. We used Flex, and it looks like a truck of Flex exploded in the attic.

    Last year we put a 2 ton unit in a 1500 sq/ft house. I'm just getting confused as to how am I supposed to set these A/C units up correctly if they (which I belive) are not sized properly?

    I did a heat load using Easy A/C 2.0 (I have a Mac, it's the only software that I can find, and I love my Mac.) I plugged in the information and I get that a 1.5 ton A/C would be suffecient for that house given the heat load of the house.

    So I am looking for someone to help me determine how I am to tackle these issues, not just this one in particular, but to learn so that in the future I am better equipped to handle these things. Thanks beenthere

  4. #17
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    Jan 2004
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    Lancaster PA
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    OK, when read the term sub cool, it just made me thing you were reading the lquid line, but you just termed it wrong, sorry about that.

    Next, your chart isn't the only chart that doesn't show 55 wb at 85 od.

    I would have stopped at about 9 degrees superheat.

    14" round return is a little small for 3 tons.
    The supplies, depending on length are about right for the tonnage.


    As for the size that was put in, it sounds grossly over sized.
    And your 1.5 sounds right, but thats just a guess from my chair.

    Are you using a digital sling.
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  5. #18
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    Jul 2004
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    Poughkeepsie, Ny
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    Originally posted by beenthere
    OK, when read the term sub cool, it just made me thing you were reading the lquid line, but you just termed it wrong, sorry about that.

    Next, your chart isn't the only chart that doesn't show 55 wb at 85 od.

    I would have stopped at about 9 degrees superheat.

    14" round return is a little small for 3 tons.
    The supplies, depending on length are about right for the tonnage.


    As for the size that was put in, it sounds grossly over sized.
    And your 1.5 sounds right, but thats just a guess from my chair.

    Are you using a digital sling.
    I know about the chart, when the other tech did the charge, evac, and sweep he said that it was charged ok and that I may want to check it. I know for a fact that he uses the 20 deg. over ambient.
    I have a mercury sling, I did by the return in the house after the unit ran for a little bit. Then I went outside, hooked up my guages, and thermometer and did my dry bulb. That is when I stopped. Because I had an inkling that the a/c was overkill and I wanted to get the specs on the house to verify that inkling.

    I just wrote down my readings and left because I didn't want to charge it and flood or slug the compressor, and I didn't want to remove refrigerant because I wasn't sure if that was the right thing to do.

    I heard that maybe slowing down the blower will help, but that is a big maybe and will problably turn the house into a meat locker. Or ice the coil up on humid days.

    Although I didn't understand that the supplies are correct for the tonnage but the A/C is oversized? Or do you mean that the whole thing is just wrong from the begining? Or the supplies are correct for the sq/ft to cfm requirement and that the a/c cooling capacity is oversized?

  6. #19
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    Slowing down the blower, might help alittle, but not much.

    I meant the supplies are about emough to deliver the cfm of air a 3 ton unit needs. Has nothing to do with the over sizing of the unit.

    A 3 ton unit generally needs aprox. 1200 cfm.

    On average you need 400 cfm per ton, this varies with the climate area your in.
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  7. #20
    Join Date
    Oct 2001
    Location
    Waterford Michigan
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    This is a good example of why HVAC has such a bad name; unqualified people installing oversized equipment.

  8. #21
    Join Date
    Jul 2004
    Location
    Poughkeepsie, Ny
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    631
    Originally posted by johnl45
    This is a good example of why HVAC has such a bad name; unqualified people installing oversized equipment.
    This is why I am here to find out the correct way to install and size A/C units. I don't want to be classified with those who are ignorant and refuse to learn or change. I want to size, install and service my work in the most professional manner possible. But when your handed a botched job, how do you make it work, or is it just impossible. That brings me back to the it should have been done right to begin with.

  9. #22
    Join Date
    Apr 2004
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    Several things since you seem willing to accept some advice. Fist off, the fan speed selection is your job, the mfg has to connect it somewhere, they cant just leave the wire hang. On top of the unit being oversized (which should be corrected or plan on a lifetime of disapointment).

    Next you probably have an airflow issue. 7 inch flex if installed properly (stretched and straight) is good for maybe 110-120 CFM tops and I doubt your even there if it looks as you described it. the 6 is 70 or 80 at best. This means at best you have no more than 920 CFM in supply ducting. If the return is 14" then its good for about 700 or 800 which also is hurting you and together its a compressor killing installation.

    Now even after all that, in a low load situation like you have, your suction is too high and your head too low. The piston that came with the coil is not always the right one. That coil can probably be matched to numerous units. Install the correct oriface per the installation instructions (You may have to get another copy as it sounds like the original ones were thrown away with the box prior to connecting the system). Better yet, disconnect the entire unit and install the right unit (which by the way your duct is sufficient for). Otherwise install another 300-400 cfm supply and blow it outside and add another 14" return.

  10. #23
    Join Date
    Nov 2003
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    125

    Confused

    Just wondering.
    Did your company install a 1 1/2--2 ton system on @ a 1500 sq.ft house that week!???

  11. #24
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    Lancaster PA
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    Doc, teh guy is just starting in the trade, his boss ain't going to pull that thing and install another one on his say so.

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  12. #25
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    Jul 2004
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    Poughkeepsie, Ny
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    Originally posted by docholiday
    Several things since you seem willing to accept some advice. Fist off, the fan speed selection is your job, the mfg has to connect it somewhere, they cant just leave the wire hang. On top of the unit being oversized (which should be corrected or plan on a lifetime of disapointment).
    Usually the boss tells us to change the speeds when we do the install. Unless he say so, we no change.

    QUOTE]Originally posted by docholiday
    Next you probably have an airflow issue. 7 inch flex if installed properly (stretched and straight) is good for maybe 110-120 CFM tops and I doubt your even there if it looks as you described it. the 6 is 70 or 80 at best. This means at best you have no more than 920 CFM in supply ducting. If the return is 14" then its good for about 700 or 800 which also is hurting you and together its a compressor killing installation.[/QUOTE]

    That is why I just stopped. I had an inkling that something was wrong in the beginning. Then when I did the superheat, it was like yup, this is worse than I thought. So I backed away.

    QUOTE]Originally posted by docholiday
    Now even after all that, in a low load situation like you have, your suction is too high and your head too low. The piston that came with the coil is not always the right one. That coil can probably be matched to numerous units. Install the correct oriface per the installation instructions (You may have to get another copy as it sounds like the original ones were thrown away with the box prior to connecting the system). Better yet, disconnect the entire unit and install the right unit (which by the way your duct is sufficient for). Otherwise install another 300-400 cfm supply and blow it outside and add another 14" return. [/QUOTE]

    Ha! That's good. But I don't think that the homeowner would like that. Hey, it's his bed, let him lay in it. He sized it, sold it and ordered it. I'm just the lackey that installed per his instructions, hopefully only this time.

    Hey, I'm no expert in A/C, but I can understand theory and practical application. I read books and try to get as much schooling as I can to learn that little nugget that will help me in the future. There are methods that come up and work. If they are theoritically practical, they'll probably work and be reliable. I'm looking to learn anything on how to do my job better, make my company look good and walk away from a job knowing that It was done right. -I'll be stepping off my soap box now..

  13. #26
    Join Date
    Apr 2004
    Posts
    7,680
    Originally posted by beenthere
    Doc, teh guy is just starting in the trade, his boss ain't going to pull that thing and install another one on his say so.

    Hmm ok, I'll buy that but I bet the customer who wrote the check doesnt give a rats arse about this kid because he paid for an istallation assuming it would be completed by professionals. No crack on the kid, like he says, he just does what he's told, and I believe him. We were all new but being new doesnt mean you can get away with a poorly installed and set up system. His boss is who I have a problem with. He's the one who charged the customer and hes the one who sent them out there when they werent ready.

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