Carrier variable speed dehumidification questions
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  1. #1
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    Carrier variable speed dehumidification questions

    Hi all,
    I will try to keep this short and simple, long story at the bottom.

    1) Originally had r410a Carrier Comfort package installed. (FX4D air handler with TXV. 25HCC530A300 Comfort heat pump.)
    2) Contractor swapped out the motor from the air handler for a variable speed motor from the FV4CNF air handler. He also swapped over the Smart Board as well.
    (Contractor says that the only difference between the two air handlers is the motor and the control board. So now I should effectively have an FV4CNF air handler.)
    3) Contractor also installed an Ecobee smart thermostat.

    Here's where I'm at: The contractor refuses to hook up the dehumidify output of the thermostat to the Dh terminal of the air handler for dehumidification. His reasoning is that this can ONLY be done if the heat pump is a 2 speed unit, whereas mine is only a 1 speed heat pump. He's telling me that if I do this, the air handler will make the fan speed too slow and it will cause my coil to freeze up when the air handler is trying to dehumidify. He's telling me it will freeze up just like when the filter is clogged and the airflow is too low. Is this nonsense? I have read two threads where I think people are doing exactly this here and here.

    Please help,

    Thanks all!
    Last edited by CoolIsGood; 10-26-2010 at 11:43 AM.

  2. #2
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    I do not know. but it seems to me it should work. unless he already has the air volume dialed down to the ragged edge. maybe the logic of the board dropps to below first stage with a call for dehumidify?

  3. #3
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    Quote Originally Posted by fearlessfurnace View Post
    I do not know. but it seems to me it should work. unless he already has the air volume dialed down to the ragged edge. maybe the logic of the board dropps to below first stage with a call for dehumidify?
    Is my heat pump 2 stages? My contractor seems to think that it's only 1 stage and 1 speed.

  4. #4
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    Can you post the serial numbers,on each?

  5. #5
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    Hopefully your contractor is right and its a single stage. Its not one of those things you usually see overlooked.

    Now he has played "carrier field engineer" with your unit, hopefully that is correct about them being identical except for motor/board/blower wheel.

    Usually single stage units do not ice up with a call to dehumifidy.

    Unless unit is on the ragged edge of icing at 100%.

    And it is quite common to utilize that feature

  6. #6
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    Quote Originally Posted by amasuperbike View Post
    Hopefully your contractor is right and its a single stage. Its not one of those things you usually see overlooked.

    Now he has played "carrier field engineer" with your unit, hopefully that is correct about them being identical except for motor/board/blower wheel.

    Usually single stage units do not ice up with a call to dehumifidy.

    Unless unit is on the ragged edge of icing at 100%.

    And it is quite common to utilize that feature
    Well I am hoping my contractor is wrong. According to this website, I think it might actually be a two stage. And this PDF file here says that comfort series heat pump can be equipped with 2 stage, just look at the bottom of page 3.

    Regardless, even if it isn't a two stage heat pump, are you saying that I'm pretty safe with hooking up the dehumidify function of the thermostat to the Dh terminal of the air handler?

  7. #7
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    we an't going to tell you to mess with wires.
    we hate it when custumers screw with our installs.
    but we all seem to kinda-sorta think your guy is wrong.
    nobodys perfect.
    but we are not there. we could be wrong. we could be missunderstanding you.
    i've been wrong lots of times on the job

  8. #8
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    Quote Originally Posted by CoolIsGood View Post
    Well I am hoping my contractor is wrong. According to this website, I think it might actually be a two stage. And this PDF file here says that comfort series heat pump can be equipped with 2 stage, just look at the bottom of page 3.

    Regardless, even if it isn't a two stage heat pump, are you saying that I'm pretty safe with hooking up the dehumidify function of the thermostat to the Dh terminal of the air handler?
    Maybe some are 2stage and other models/sizes are not.

    Sounds like you need a 2nd opinion from a new fresh contractor.

    You can ask him if he sees any obvious airflow issues and make sure you can hook up your dehum feature without any issues.

  9. #9
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    Well according to this carrier document about the 25HCC5, it doesn't seem to say anything about two stages, so it looks like I have a one stage heat pump.

    I'm not interested in playing around with the wires myself. I want my contractor to come back and do it RIGHT. But, so far I have lost trust in him.

    How likely is it that my coil will freeze up as my contractor says if the air handler drops the fan speed during a dehumidify cycle? Should I just go ahead and demand for him to hook up the dehumidify function of the air handler?

  10. #10
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    Just called a different carrier contractor over the phone and he told me that the whole freezing thing is nonsense. He even supplied me with AHRI #3676240 showing that my heat pump can be matched with the FV4CNF air handler. He says that it absolutely doesn't need to be a two stage heat pump to use Dehum feature of a VS air handler.

    Now just to convince my contractor to come here and rewire the darn thing...

  11. #11
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    worst comes to worse it freezes. you pay your guy to put it back his way .

    and we all look realy realy dumb

  12. #12
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    You dont have a FV4CNF air handler.

    And noone can tell you w/o looking at your install and taking some readings whether you are in danger of icing.

  13. #13
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    Quote Originally Posted by amasuperbike View Post
    You dont have a FV4CNF air handler.

    And noone can tell you w/o looking at your install and taking some readings whether you are in danger of icing.
    Yes I do, it says so right on the front of the air handler's cabinet.

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