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Could someone confirm my understanding of how B & O change over lines are supposed to work.

O is powered from RC when cooling is needed (looks like it mirrors Y)
B is powered from RC when heating is needed

Is this correct?

Thanks
 

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in a single transformer system RC/RH should be jumped and it wont matter because the power comes from the B/O terminal in your stat.
the reversing valve will be spring loaded and will only be powered in one mode, returning to default in the other. you need to determine which way your valve is defaulted and supply power as needed.
 
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