What voltage would be measured from terminal Y to the input side of the coil on line #11 when the thermostat is closed and the fan is in auto?

When the thermostat is closed and the fan is set to auto, the system is completing its electrical circuit to energize the coil, which typically operates at a standard voltage. In this scenario, if the line referenced is part of a common residential or commercial setup, the output voltage from the transformer supplying power to the thermostat and thereby to the control circuit is usually 24 volts. However, measuring from terminal Y (which typically represents the call for cooling or heating) to the input side of the coil on line #11, you might encounter 120 volts if that line is part of the higher voltage circuit that supplies power to the system components like the compressor or fan motors.

If the setup involves a 120-volt supply to the control circuit that includes the thermostat, measuring directly across these terminals would reflect that 120 volts, provided there is no load on the line. This indicates that the fan and any other circuit controlled by the thermostat will receive sufficient voltage to operate when the thermostat activates the system. Hence, the answer indicating 120 volts as the voltage measured from terminal Y to the coil's input when the system is operating is a reflection of the typical wiring and voltage supply configuration in such HVAC systems.