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  1. #1
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    Static pressure troubles

    Most all of the systems it seams like I am testing static pressure in cooling are over the design static of the manufacturers system design. Several I can't adjust down far enough and still get the cfm for the rated coil. Is it safe to reduce the airflow this much? I think I may be asking for trouble? Although I feel I am doing the right thing to make these adjustments. Most are return issues. The first clue is the noise and that gets it started to test. Thanks

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  3. #2
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    Quote Originally Posted by LRB View Post
    Most all of the systems it seams like I am testing static pressure in cooling are over the design static of the manufacturers system design. Several I can't adjust down far enough and still get the cfm for the rated coil. Is it safe to reduce the airflow this much? I think I may be asking for trouble? Although I feel I am doing the right thing to make these adjustments. Most are return issues. The first clue is the noise and that gets it started to test. Thanks
    What is the actual tesp and what is the design? Some (carrier i believe) will say test at on the name plate but the fan curve chart will go upto .9


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  4. #3
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    Something like this?


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  5. #4
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    Ameristar is .50 and my readings are 1.09 on High and even on Med High I am at .94

  6. #5
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    Quote Originally Posted by LRB View Post
    Ameristar is .50 and my readings are 1.09 on High and even on Med High I am at .94
    That is too high. Bound to have problems. I wouldn’t condemn ducting based on name plate static alone though. Unless its an easy fix.


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  7. #6
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    Thread Starter
    There are 3 systems and I am assuming the other 2 have adjusted some of the temperature and humidity. Is it logical to reduce the speed anymore?

  8. #7
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    That test static number looks like something they use at the factory to get the rated capacity out of the unit. So, and I am assuming here, that means your numbers change as the static increases.

    But that's not always as bad as it may seem. Because, if I'm not mistaken, as the airflow decreases, the sensible load decreases and the latent load increases. So if you are in a high humidity area, it could actually be beneficial.

    I welcome others to add or correct me if I'm wrong.

    Where I live, we very rarely have "too high of humidity's", so a restricted airflow like that would really cut down on the capacity of the unit. Just means you're gonna be paying for it to run longer.


    Quote Originally Posted by Core_d View Post
    Something like this?


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    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  9. #8
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    I'm good with leaving it on HIGH but ultimately where is the happy ending? Too much is ok? I had one customer last week say the fan adjustment helped her 2nd floor in 90 plus. This week I had a customer say it took away from an office but the rest of the house was fine? Really difficult trying to make it right......

  10. #9
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    You haven't told us anything about the system.

    Yes, increased airflow can decrease airflow at a register while increasing it at another register. If you don't understand that, let me know, and I'll draw you a picture of why.

    If it is an ECM or X13 motor, the high static will dramatically shorten the life of the blower.

    There can be a lot going on here that don't have a clue about.

    Where I live, most heating is done with natural gas, so in a residential setting, I'd be setting the blower to be within the temp rise of the gas fired heater. Then adjust the A/C to work well enough with that airflow.


    Quote Originally Posted by LRB View Post
    I'm good with leaving it on HIGH but ultimately where is the happy ending? Too much is ok? I had one customer last week say the fan adjustment helped her 2nd floor in 90 plus. This week I had a customer say it took away from an office but the rest of the house was fine? Really difficult trying to make it right......
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  11. #10
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    I actually reduced the speed. It's a PSC 4 speed motor 3 ton 16x14 return into a 20x16 filter box. Supply is 19x21. I have not tested the velocity yet.

  12. #11
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    That's purdy darn close to what I have in my house. I run the cooling on the lowest speed, and the heating on the highest speed. Not that that has anything to do with your system; I'm just Special.


    Quote Originally Posted by LRB View Post
    I actually reduced the speed. It's a PSC 4 speed motor 3 ton 16x14 return into a 20x16 filter box. Supply is 19x21. I have not tested the velocity yet.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  13. #12
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    Does that add moisture to the house in CA? I will drop it to MED LO and see what happens. I would think it would run longer?

  14. #13
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    Just the opposite. With my blower on the lowest speed, that will reduce the relative humidity. But it will also increase the temp of my house.

    So I'm happy with the trade off. The house can very comfortable at a few degrees higher with the lower humidity's.

    The reason I run the heat on high, is because the heat was stratifying high in the room, and no heat was getting down to me while in my recliner. So I need the blower on high to mix the heat well; I just dialed in the cooling with the blower on low and it worked out real sweet.


    Quote Originally Posted by LRB View Post
    Does that add moisture to the house in CA? I will drop it to MED LO and see what happens. I would think it would run longer?
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

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