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  1. #1
    Join Date
    Jan 2010
    Location
    Ocean City, Maryland
    Posts
    5

    Confused Flaky variable fan speed controller on XL14i

    We have a Trane XL14i heatpump and lately the variable speed motor rpms have been fluctuating high/low approximately two minutes from the end of the heating cycle.

    Aside from the fact that the engine speed controller is malfunctioning, it is irritating because you can really hear the rush of air in the ductwork each time the motor changes from low to high rpms.

    The technician tested the controller somehow but said it is OK when obviously it is not.

    There is a video here with a piece of paper taped to the top of the heat register to better show the airflow: Airflow problem

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,741
    Has it always done this.
    How long has it been installed.
    How cold is it outside. could it be that the last 2 minutes of run time. the aux heat is also on?
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  3. #3
    Join Date
    Jan 2010
    Location
    Ocean City, Maryland
    Posts
    5
    It was installed new in July 2007. It has just started recently. The temperature is about 32 degrees outside and so the auxillary heat does not ever need to come on. I would see "Aux Heat" displayed on the LCD of the thermostat of the strips came on.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,741
    You'll need a good tech then. One that doesn't give up after just checking one thing.
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  5. #5
    Join Date
    Apr 2009
    Posts
    523
    If the electric heat NEVER comes on then why did you have it installed? Fact of the matter is you are in a state that uses aux heat quite often. I know this because I'm about 2 hours away from you. Anyway the reason I say this is because the fan will ramp WAY up for electric heating.

    Now I'm not saying you are wrong and everything is perfect but think about it this way. The fan ramps up to high about 2 minutes before the cycle ENDS. How could a malfunctioning part KNOW when the call is going to end? The unit doesnt know when its going to shut off, it keeps running until the thermostat tells it to shut off.

    So why would it end two minutes after ramping up? The simplest explanation is that the air temp is increasing and satisfying the call. The air temp would only increase from heat pump heat with the use of aux heat.

    And the fact we are seeing temps here well lower then they have been since 2007 (when the system was installed).

    I'm just saying. You need a tech you have confidence in, either they will in fact find a problem or at least explain the operation of this thing better. If nothing else check some things and see if they can lower the high fan speed to a more reasonable decibel level.

    If you want to test something yourself, wait for the heat to come on like you like it. Then bump up the thermostat 3-4 degrees and see if it does what you are experiencing. Bumping up the temp will activate the electric heat, and should increase the blower speed...

  6. #6
    Join Date
    Jan 2010
    Location
    Ocean City, Maryland
    Posts
    5
    The problem is not that the fan speed changes from low to high two minutes before the heating cycle ends. The problem is that two minutes before the heat cycle ends the air handler fan constantly changes from high - low - high - low - high - low - high over and over about every 5 seconds during the last two minutes. It is clearly evident in the video link I posted at about the 20 second mark.

  7. #7
    Join Date
    Jun 2003
    Location
    Morehead City, North Carolina
    Posts
    174
    Is this installed with a zone system?

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,741
    Chuck. You should have a Harley as your avatar.
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  9. #9
    Join Date
    Nov 2009
    Location
    Lexington,Ky
    Posts
    23
    could possibly be a board issue

  10. #10
    Join Date
    Jan 2010
    Location
    Ocean City, Maryland
    Posts
    5

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    Good idea. Done!

    Quote Originally Posted by beenthere View Post
    Chuck. You should have a Harley as your avatar.

  11. #11
    Join Date
    Jul 2009
    Posts
    247
    Has anybody gone through and closed off a bunch of vents to try and push air elsewhere? How's your air filter look?

  12. #12
    Join Date
    Jan 2010
    Location
    Ocean City, Maryland
    Posts
    5

    Thumbs up

    Problem solved. Our local Trane dealer made a service call today and quickly isolated the problem to a "short" in the old thermostat. Unwanted stray signal voltages were being sent through the control lines up to the controller board in the air handler. I was very impressed with their troubleshooting and customer support. If you are reading this, thanks guys.

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