An HVAC controller includes a first input terminal configured to be electrically coupled with a first field wire and a second input terminal configured to be electrically coupled with a second field wire, and a double pole relay including two input terminals and two output terminals. Control circuitry is operably coupled to the temperature sensor and the double pole relay and is configured to determine whether the first field wire is electrically coupled with the first input terminal and whether the second field wire is electrically coupled with the second input terminal.