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Lennox Harmony II zone control

Devan Member Posts: 138
On a recent project, replaced hot water heting system , replaced honeywell round heat/cool thermostats and upgraded thermostats to electronic heat/cool stats.

Testing the system found the existing Lennox Harmony II zone control and Lennox CB21 air handler not working in cool mode.

Going thru the controls I see previous a/c contractor only used R & Y terminals in Harmony control.

Not sure if I have to add a relay between my new stats?? Any help appreciated.



  • JStar
    JStar Member Posts: 2,752

    How are the wires connected at the A/H zone board and t-stat? How were they wired before? Did you shut down the A/H power before changing the stat? Maybe you shorted a wire and (hopefully) popped a fuse.
  • Devan
    Devan Member Posts: 138
    LED's on

    so zone control board seems to be powered up.

    From thermostat into control board only R&Y were used. Since I was not doing any additional AC work, I really did not look into the board until now. Old thermostats only use R&Y as well, but I did connect R,Y and G to the new stat., but at the Harmony board G was not used.
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