Ultrasonic leak detectors locate refrigerant leaks by:

• A. Hearing the high frequency of escaping gas.
• B. Measuring the leak rate with a flowmeter.
• C. Sampling refrigerant concentration in the air.
• D. Visually inspecting the system for bubbles.

Answer: (A)

Ultrasonic leak detectors locate leaks by listening for the high-frequency noise produced when pressurized refrigerant escapes through a small opening. The escaping gas creates a fast, turbulent jet that emits ultrasonic sound waves (above what humans can hear). The detector uses a microphone or sensor tuned to those ultrasonic frequencies and signals when it detects the sound, enabling leak location even on small leaks while the system is running. This is different from methods that rely on flow measurements, air sampling for refrigerant concentration, or visual bubble tests, which do not detect the acoustic signature of a leak.