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c wire

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DaveM
DaveM Member Posts: 77
in Strictly Steam

i have an old lennox t90k110c110 thermostat for cool only. the air handler i believe does not have a control board (i will check today)

my question is can i replace this with a new ecobee smart thermostat

IMG_1613.jpg

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 11,588
    edited December 1

    YES

    You may want to add a new thermostat wire if you don't already have an extra unused wire in the wall.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • DaveM
    DaveM Member Posts: 77

    thanks Ed i'm going to run 18/5 down to the air handler this is a picture of the transformer down at the unit. where would the c wire connect to thanks again for your help

    IMG_1629.jpg
  • mattmia2
    mattmia2 Member Posts: 15,647

    what is the label on the lower left terminal?

    is that blue wire connected to anything?

  • DaveM
    DaveM Member Posts: 77

    the blue wire connects to red wire out of picture going to contactor on outside unit

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,621

    C is next to R

    You can tell because G & C go to the fan coil relay to start the fan. Move the wires and you will see it is marked C

  • mattmia2
    mattmia2 Member Posts: 15,647
    https://forum.heatinghelp.com/discussion/comment/1874754#Comment_1874754

    oh, because those are the terminals of the actual xfmr.

  • DaveM
    DaveM Member Posts: 77

    thanks that makes sense ill check tomorrow

  • DaveM
    DaveM Member Posts: 77

    you are right have 24v between R & C

  • DaveM
    DaveM Member Posts: 77

    you are right thats the C terminal i have 24v between R &C

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