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  1. #1

    Confused AOP Trane Heat Pump 12 issue

    Hello everyone,

    First time poster so go easy.

    I have a 9 year old Trane Heat Pump 12 (I don't know the numbers that follow might be XL or XB) and it's been working perfectly (both in cooling and heating mode). However, on Sunday night on startup and shutdown it has been making a clunk sound a second after the fan on the heat pump starts spinning.

    It was unseasonably warm so the heat pump probably didn't run all day yesterday so I turned it on and no noise. It ran perfectly fine for a couple days without a noise and then last night (Tuesday) it made the noise again. I'm afraid if I call a tech out then he won't be able to replicate the problem and then I will still not have an answer. The unit is heating and cooling as normal.

    Do you have any idea on what could be causing the clunk on the start cycle and then when it shuts off? It doesn't do it immediately when the fan starts.


  2. #2
    Join Date
    May 2008
    Make sure your indoor air filter is clean, and if using pleated filters, change to regular non-pleated type (if 1"). Restrictive air filters will cause problems, especially in heating mode!

  3. #3
    Would that affect the outside unit as that's where the intermittent clunk is coming from? I'm just curious.

    It is about time to change the air filter. It is 1" and I use the 3M air filters that don't have the extreme amounts of pleats.

    I appreciate the help.

  4. #4
    Join Date
    Oct 2011
    south al.
    Clunks in the outdoor unit could be animals getting into the fan blades or you could have some hard starting issues in the fan or compressor.
    Best to have a tech come out and service the equipment and test capacitors to be sure they are at proper ratings.
    If your return air is properly sized for your system then any pleated filter can restrict air flow some. Best to use regular filter or over size the return grille and use a bigger filter.

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