What is the circuit designation for the airflow indicator and alarm system?

• A. AF
• B. HF
• C. AQ
• D. HL

Answer: (B)

In this labeling system, circuit designations use two letters where the second letter signals the function and the first indicates the general system area. The airflow indicator and alarm is identified by the function letter F, paired with the airflow-related system group, which is why the designation HF is used. That makes this designation match exactly what the airflow indicator and alarm circuit does—notify you when airflow is present or not. The other codes point to different systems or functions, so they don’t describe the airflow indicator and alarm circuit.