What is the purpose of the normally open set of contacts in a fan center relay?

The primary function of the normally open set of contacts in a fan center relay is to control the operation of the blower motor, specifically during high-speed operation. When the heating system is activated, these contacts close, allowing electricity to flow to the blower motor and enabling it to operate at high speed. This high-speed operation is essential for providing adequate airflow to distribute heat throughout the space, ensuring that the heating system operates efficiently and effectively.

In contrast, the other options do not accurately represent the specific purpose of these contacts. For instance, low-speed operation of the blower motor is typically managed by a different set of contacts or a separate relay, which would not be the role of the normally open contacts in a fan center relay. Similarly, regulating the fuel supply to the burner and monitoring heat exchanger temperature involve processes outside the function of the relay's contacts, as they are managed by different components and systems in the heating setup. Therefore, the correct role of the normally open contacts in a fan center relay pertains directly to controlling the high-speed operation of the blower motor.