What component load is being tested when measuring 120V across the heat terminal and neutral terminal?

When measuring 120V across the heat terminal and neutral terminal, the component that you are typically testing is the blower motor. In a standard HVAC system, the heat terminal is often connected to the control circuitry that triggers multiple components, including the blower motor itself. The blower motor is responsible for circulating air throughout the system, and when it operates during heating cycles, it generally runs at 120 volts.

The presence of the 120V measurement confirms that power is being supplied to the motor, indicating that the component is likely functioning as intended when the heat is activated. This voltage measurement serves as a critical checkpoint in the troubleshooting process, allowing you to ascertain that the blower motor is receiving adequate voltage to operate effectively.

In contrast, the other components mentioned typically serve different functions or operate under different conditions. The induced draft motor would be involved in exhausting flue gases and may not be directly connected to the heat terminal in the same way. The hot surface igniter operates under a different voltage setting and is primarily responsible for igniting the gas in a furnace. The transformer primary provides power to the control circuits of the system but does not directly relate to the 120V measurement across the heat terminal.