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Blue "C" wire is connected to "Y" on old thermostat. New thermostat has separate "C" hookup. Where does the blue wire go - "Y" or "C"? : r/Nest
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Honeywell Home C-Wire Adapter for Honeywell home Wi-Fi Thermostats and RedLINK® 8000 Series thermostats THP9045A1098 - Amazon.com
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