Noise from high-pressure line and a blower question -
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  1. #1
    Join Date
    Sep 2004
    Posts
    41
    Just a quick question on a new home and the first real time we have fired up the Central A/C -

    Noticed on the high-side supply line to the basement AHU that I can hear a strange noise every so often that sounds like air in the line. If you are touching the line during the event you can "feel" something like water in a garden hose type of thing. Really hard to describe. The system is working fine with no complaints, again, just curious if this is something I should have looked at.

    Question #2 -

    Attic AHU is set on the lowest fan speed. I believe this may have been done because I was very addiment I didn't want to hear any blowers in my bedroom(s). It's on it's own zone and is only for the 2nd floor. (It's own AHU and Condenser). Any possible problem switching from low to medium fan speed?


    Any feedback would be great. I'm really concerned about that strange noise on the head line.

    -Chris

  2. #2
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    If by high-side supply line you mean the smaller of the two copper refrigerant lines, then you're hearing gas. Don't worry. It's not a digestive problem. Most of the time that line will be a column of solid liquid. But there are many conditions that can occur to cause some of the liquid refrigerant in the line to flash and become vapor. For the first few minutes of operation you'll typically have vapor in the line. And in hot weather you'll have occasional bits of vapor. Or if it's undercharged you'll get vapor. The last one is the one to be concerned about. But if it cools well and you only occasionally hear gas then don't worry about it. Occasional gas is normal for both humans and air conditioners. Thankfully their effects are very different.

    So you have a single system divided into multiple zones? AND they've turned the fan down??? There's a potential problem there that can cause you some serious bucks down the road. You probably need to switch to high speed. I am only guessing. I'm not there. You need a competent tech that will evaluate it properly and not be afraid to tell you to deal with the noise for the system's sake if that need be the case. Read point 23 starting from the third paragraph down.

  3. #3
    Join Date
    Sep 2004
    Posts
    41
    Not a single system, sorry I should have been more clear.

    It's a hydronic system with a boiler that supplies hot-water to two separate AHU's (Basement and Attic) for heat. Then there are two separate Condenser units outside. One for the 2nd floor zone and one for the 1st floor zone.

    The 1st floor AHU fan is set on "high" which works great for heating and A/C. It is removing the humidity very well with no cycling issues.

    The 2nd floor I was a bit of a prick about when the house was built. I didn't want to hear any noise and was a PITA about being sure ducts were sized correct so the velocity wasn't crazy high like a couple of my friends systems. Which wakes them up when the blower starts. I'm assuming this is why the 2nd floor blower is set on low.

    But with it being on low it is taking an excessive amount of time to cool the 2nd floor. This is turn is going to cause my light bill to be much higher because the equipment is running MUCH longer then the 1st floor to keep up.

    I just wanted to change it to "Medium" and I would bet things would be fine. BUT with all the reading I do around here I just wanted to be sure that changing a fan speed wouldn't cause any issues.

    I am glad to hear I shouldn't worry about the "gas" in the line.

    -Chris



  4. #4
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    No. No problems will result. In fact, problems occur much more often from low airflow than from high. Too low an airflow can reduce total capacity and even damage the compressor over the long term. High airflow, especially for dry climates is nothing but a good thing (other than noise obviously). In a dry climate your sensible capacity will increase. Sensible capacity is the same thing as temperature reduction and it's all we care about in dry climates. In a humid climate your total capacity will increase but some of it will shift from moisture removal to temperature reduction. Make too big a shift and it will not remove enough humidity.

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