Automotive Service Excellence (ASE) Air Conditioner Certification Practice Exam 2025 - Free ASE Air Conditioner Practice Questions and Study Guide

The correct answer indicates that hearing a hissing noise after the vehicle is turned off is typically associated with normal behavior in an A/C system as the pressures within the system are equalizing. When the engine is running, the A/C compressor is actively compressing the refrigerant, leading to high pressure. After the engine is turned off, the refrigerant can begin to migrate back through the system, causing a temporary hissing sound as the pressures balance out.

This hissing noise is a common occurrence and does not imply any malfunction or immediate concern regarding the A/C system. It reflects the refrigerant returning to a stable state, indicating that the system is functioning as expected under normal operating conditions.

Understanding this phenomenon helps distinguish between normal operational sounds and potential issues, such as a refrigerant leak, which would typically present with different symptoms, like a continuous hissing or bubbling sound during operation.