DIAGNOSIS The Y1 (cooling) terminal is receiving constant power, likely due to incorrect wiring or a configuration setting that forces the relay closed.
FIX Check for a wiring short first.
- Turn off HVAC power at the breaker.
- At the Ecobee wall plate, verify the green G (fan) wire and yellow Y1 (cooling) wire are in their correct, separate terminals. A wire in the wrong spot or a stray strand causing a short will keep the circuit engaged.
- Also check the corresponding connections at your outdoor condenser unit's low-voltage terminals.
IF THAT DIDN'T WORK The installer setup may be wrong. On the thermostat, go to Settings > Installation Settings > Equipment > Reconfigure Equipment. Ensure you did NOT select 'Heat Pump' if you have a conventional gas/electric system. An incorrect setting here energizes the wrong terminals.
HEADS UP While troubleshooting, set the thermostat to 'Off' and turn the breaker off to prevent freezing the evaporator coil. A constantly running A/C can cause serious ice damage in under an hour.