What voltage would be found from Terminal Y to the Common side of the Contactor Coil when the thermostat bulb is closed?

When the thermostat bulb is closed, it typically completes a circuit to allow current to flow to the contactor coil. The standard voltage used in many HVAC systems for control circuits, including those for contactors and thermos, is 24 volts.

In this context, when the Y terminal (which often represents the cooling signal in a thermostat) connects to Common (which is usually the return path or neutral), the voltage read between these two points would indeed be 24 volts. This is a common configuration in residential and commercial HVAC systems, where low-voltage control is used to operate components like contactors and relays safely.

Understanding the standard voltages in HVAC systems is crucial, as connecting to incorrect voltages could lead to equipment malfunction or damage. Thus, the identification of 24 volts as the voltage present between the Y terminal and Common when the thermostat bulb is closed reflects standard practice in the field.