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

Charging the A/C system through the low side can be done both when the engine is on and when it is off. This flexibility allows a technician to accommodate different service procedures depending on the specific situation.

When the engine is off, the charging process can be conducted without the need to contend with system dynamics such as pressures varying due to the compressor operation. This can be useful for adding refrigerant in a controlled manner, especially when working on systems that may not have a functioning compressor or are otherwise inoperative.

Conversely, charging with the engine running allows the technician to charge the system while monitoring the pressure readings on the gauge. This can help assess the system's performance in real time and allows for more accurate charging to the manufacturer's specifications.

A certified technician will typically choose the method based on the condition of the vehicle and the A/C system, along with safety considerations. Hence, there's no restriction on charging exclusively with the engine on or off, making it permissible in both states.