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  1. #1
    Join Date
    Jun 2005
    Posts
    42
    About a month ago, I replaced my old furnace and A/C with a new 5 ton air conditioner and furnace installed with a furnace-mounted media filter. In the beginning, the motor was very quiet. However, I have started hearing a high pitched noise when the unit is running as well as some noises when the motor and blower wheel are getting close to stopping. The furnace is in a closet. The furnace has a variable speed motor and is rated for a maximum static pressure of .8 in. w.c. I have just found out that my new system has a static pressure of approximately 1.0 in. w.c. which is about 25% over the maximum rated for the system. What could be some reasons for why the noises have started? Could the excessive pressure be causing the motor to start being noisy? What kinds of problems show up when a variable speed motor is operated above the maximum static pressure? Any input would be appreciated.

  2. #2
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,031
    What could be some reasons for why the noises have started? Could the excessive pressure be causing the motor to start being noisy? What kinds of problems show up when a variable speed motor is operated above the maximum static pressure? Any input would be appreciated.
    The excessive ESP is destroying the VS motor and wheel. Get the ductwork fixed. Replace the motor.

  3. #3
    Join Date
    Dec 2001
    Location
    Ocean Pines, MD
    Posts
    6,935
    You sure your not hearing the refrigerant flow? Maybe it is getting low and hissing at the TXV? Try turning off just A/C unit's breaker while running.

  4. #4
    Join Date
    Apr 2004
    Location
    Midwest
    Posts
    2,682
    The excessive ESP is destroying the VS motor and wheel. Get the ductwork fixed. Replace the motor. [/B][/QUOTE]

    That is about as clear as it gets IMO.

    Number 1 killer for VS motors is high static, followed closly by moisture.
    Live each day like it is your last, for one day you will be right!

  5. #5
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,510
    jrbenny is right have some one fix you duct problem or you will be replacing motors and these motors are not cheap

  6. #6
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The motors themselves don't actually fail, but when you get over about .9 in WC ESP, the module will start to "hunt" and will eventually fail. I have never seen a bad ECM2 motor, but have found lots of dead modules.

    The module is easy to replace, usually without even fully removing the blower assembly from the furnace.

    Running at a high ESP can also cause the blower wheel to fail, wich can cause lots of strange noises.
    If more government is the answer, then it's a really stupid question.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,821
    Just wait till the media filter gets dirty, the noise will get worse.

    Too many contractors use VS as a cure all for bad duct systems.

    Have the duct system evaluated, and see if you can add more return, and supply as needed.

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    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,031
    Originally posted by mark beiser
    I have never seen a bad ECM2 motor, but have found lots of dead modules.
    I've seen a few. We used to require all of these returned on in-warranty failure. I like to test them just to see what was there. Vast majority were bad modules. However, I have seen my share of bad stators. They die from moisture. They're tough otherwise.

  9. #9
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Originally posted by jrbenny
    I have seen my share of bad stators. They die from moisture. They're tough otherwise.
    Ahhh, I havn't found one that got water in it. When I find a dead module, it was killed by the duct system or lightning.
    If more government is the answer, then it's a really stupid question.

  10. #10
    Join Date
    Jun 2005
    Posts
    42
    First, thank you very much for all of your input. I checked the possibility of the noise being the refrigerant flow by turning off the A/C unit’s breaker while running. I can still hear the noises even when the condensing unit is not running.

    From your answers, there seems to be a problem with the ductwork. When the static pressure measurements were done, the plenum measurement was .34 in. w.c. with the variable speed motor set on the factory setting of 1985 cfm. I have about 7.5 sq. ft of return air grills. My house is 40+ years old and has the original rectangular metal ductwork that is wrapped on the outside with fiberglass and an aluminum (?) outer layer. I have not noticed any of the ductwork being collapsed. When the old system was pulled out, I looked at the ductwork at the start of the plenum. There were turning vanes at the first right angle and the first ‘T’ in the ductwork near the plenum.

    From what I have been told, the static pressure at the plenum is higher than normal. What is a normal pressure at the plenum? What kinds of things would cause the high static pressure? Are static pressure measurements taken at different parts of the ductwork to determine where the problems are? Are there cameras that can go into the ductwork to evaluate the system? What kind of questions would I ask when I am interviewing a company to make sure it is the one to hire to find the problems and fix them? Thanks again for your help.


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