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  1. #1
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    Blower Cuts Out In Cooling

    Carrier 48TFE012-A-611 ser 1004G50704
    This unit will run for about 1 minute normally and then the blower will cut out. The contactor for the blower motor has 27 volts at the coil until it cuts out. Then it shows no low voltage. The compressors and condenser fan motors will continue to run until the unit cuts out on low pressure. The blower will not come back on until you cut power to it from the disconnect and then reestablish power. It looks like to me, the only thing that could cause this condition is a bad board. I haven't seen this before and was hoping that one of you have. If you need all of the gauge readings and etc, I have them but I didn't post them since I don't think they are relevant to the problem. Thanks in advance!

  2. #2
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    Rochester, NY
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    Are you losing voltage at G when the blower cuts out?

    The only advice I could give without being there is just look at the wiring diagram and trace back what's providing 24 volts to the coil.

  3. #3
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    Rochester, NY
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    Nevermind that question...Forgot you need 24 volts to G on a carrier for the compressor to start.

  4. #4
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    Quote Originally Posted by pvc1984 View Post
    Nevermind that question...Forgot you need 24 volts to G on a carrier for the compressor to start.
    That must be a Resi thing. Not true on the RTU's.
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  5. #5
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    Quote Originally Posted by timebuilder View Post
    That must be a Resi thing. Not true on the RTU's.
    some Carrier RTU's do need 24v at G for the compressor to run, I've worked in a few of them.

  6. #6
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    Quote Originally Posted by valdelocc View Post
    some Carrier RTU's do need 24v at G for the compressor to run, I've worked in a few of them.
    Post a model # when you have a chance. I've never seen one.
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  7. #7
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    Quote Originally Posted by valdelocc View Post
    some Carrier RTU's do need 24v at G for the compressor to run, I've worked in a few of them.
    So if you were to set the t-stat to fan on the compressor will start ?
    Or are you saying Y & G at stat ?

  8. #8
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    Quote Originally Posted by VTP99 View Post
    So if you were to set the t-stat to fan on the compressor will start ?
    Or are you saying Y & G at stat ?
    nope mechanical cooling control interlocked with fan contractor, very simple stuff! sooner or later you'd run into one.

  9. #9
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    Quote Originally Posted by VTP99 View Post
    So if you were to set the t-stat to fan on the compressor will start ?
    Or are you saying Y & G at stat ?
    If you jumper R to Y at the board of the RTU. The compressor won't run, unless the blower contactor is in also.

    First time you run into one, it throws you off.
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  10. #10
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    Quote Originally Posted by flanders View Post
    Carrier 48TFE012-A-611 ser 1004G50704
    This unit will run for about 1 minute normally and then the blower will cut out. The contactor for the blower motor has 27 volts at the coil until it cuts out. Then it shows no low voltage. The compressors and condenser fan motors will continue to run until the unit cuts out on low pressure. The blower will not come back on until you cut power to it from the disconnect and then reestablish power. It looks like to me, the only thing that could cause this condition is a bad board. I haven't seen this before and was hoping that one of you have. If you need all of the gauge readings and etc, I have them but I didn't post them since I don't think they are relevant to the problem. Thanks in advance!

    Does that unit have the fan contactor/ timer assembly. It just a fan relay with a small board
    attached to it.

    If it does or it gets it out put from a board jump the fsn coil wire to R to keep it running and then monitor the out put at the board.

    Not much to those Carrier RTUs.

  11. #11
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    Go to the economiser board if it has the 4 LED`s on it and bypass the G terminal so the board doesn`t control the fan. Then look for corrosion on it. Change as neccessary.
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  12. #12
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    Jan 2010
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    Check the fan logic for power in and out also the blower relay. Check t-stat as well.

  13. #13
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    Mar 2010
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    Arnold, Mo
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    Thanks for the replies. I'm going back today so I'll let you know if your suggestions worked.

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