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  1. #1

    blower motor speed

    I really don't have a vast knowledge about HVAC systems, I know very little. Maybe someone can help me out. I have a York air handler...model number "ahe36c3xh21". My outside unit is a Luxaire LX Series TCJF Model (which is also 3 ton). What I would like to know is how do I go about finding out what the minimum speed I can set the blower motor to, because the pressure that comes out of the ducts is way too high for me. Is it possible that if the speed is set too low that it could cause damage to the system? Is there more information that is needed?

    I appreciate any and all input

    Thanks

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,319
    Really you need a tech with some way of measuring duct static pressure before changing speeds. Odds are, the dealer left it on high (out of 5 speeds) which depending upon how restrictive your duct system and filter are, could be a bit much for a 3 ton A/C. But there's a big drop going to speed 4 and if the ducts are really restrictive, that could be too little for a 3 ton. Sounds like the unit is oversized or underducted. I'd have the installer out, again making sure the tech has the manometer or magnahelic for checking duct static and have them adjusted it properly.

  3. #3
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    The motor speed taps are used for setting speed but the real questions remain unanswered. You didn't say whether you're heating or cooling and if heating is it by heat pump or hydro-air? Minimum airflow requirements are generally needed for the equipment side of things, particularly heat pumps and air conditioners and yes, you could do damage if the speed is set too low.

    The noises you're hearing are the result, as you've already deduced, of high airflow/velocity. Changing blower speeds can have many varied results, among them changing the actual static pressure of the system. This could lead to actually moving MORE air with a slower blower, something that is counter intuitive but is related to aerodynamics. Lower speed, much less resistance to airflow = more gross airflow.

    If you were my client, the first thing I'd need to do is a load analysis to find out if the equipment is properly sized. If yes, then we would proceed to static pressure testing in conjunction with a comparison of a proper Manual 'D' design against what you have in your home. Likewise, Manual 'T' could be of assistance at just relieving the restrictions imposed by supply outlets and grilles having lower free airspace. We recently reduced the noise in a clients master bedroom because the face velocity on the supply outlets was too great. We changed the outlets to a different style and the results were striking, the customer happy and all at minimum cost. So in your case, I'd recommend someone who really knows airflow and is familiar with the various supply outlets (diffusers and registers) and return grilles.
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  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,337
    Good chance your duct work is under sized for a 3 ton unit. Or, your 3 ton unit is over sized for your duct system, and house.
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