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York Furnace P3UGD16N09001B (Circa 1989) with AC

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MelR
MelR Member Posts: 1
in Gas Heating
This model uses a S1-02521911701 transformer that has the wiring block integrated with it that is fried with 120V present on the primary side and 0V on the secondary side due to a short and so I have ordered a new one. The current tstat is the original mercury tube one using only R,G,Y,W terminals. What is confusing to me is that the wiring block has nothing attached to its Y terminal and the Y wire to the tstat and two heavier gauge wires attached to the C terminal. I wish to change out the tstat to a programmable one that needs a C wire for constant 24V. There is a spare blue wire in the loom, but it doesn't have continuity to the tstat end, so I wanted to go with the add-a-wire kit to be able to end up with the new stat. When I tested the wiring at the block before the short, I saw 24V between R and W, R and W and R and G, 0V between R and Y. How the heng should the wiring block be wired and why was the block wired this way?

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  • JUGHNE
    JUGHNE Member Posts: 11,062
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    Do you have AC and a tstat with AC cooling switch?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,540
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    If you get the same part:
    R on the term block goes to R on the thermostat
    C (common) on the term block goes to C on the thermostat
    Y on the terminal block goes to Y on the stat
    G on the terminal block goes to G on the stat

    You will have other wires on those same terminal block connections. Leave them alone or reconnect them as they are now
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
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    On the older single speed furnace Y terminal was just bug or connection screw to connect wire to condenser. You did not need to connect to Y at the airhandler . Today the Y would put the fan on high speed as well as powering a contractor in the condenser and the wire back from condenser was connected to common for the contractor .

    There was an error rendering this rich post.

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