Technician A says evacuating (pumping down) an air-conditioning system removes air and moisture from the system. Technician B says evacuating must be done anytime the system has been opened for repairs. Who is correct?

In the context of air conditioning systems, evacuating or pumping down is a critical procedure that involves removing air and moisture from the refrigerant system. This process is essential for maintaining system efficiency and preventing damage.

Technician A's statement highlights that evacuation serves to eliminate both air and moisture, which can lead to issues such as reduced thermal conductivity, corrosion of components, and the potential for ice formation. Moisture in the system can react with refrigerant and create acids that degrade the system's materials, making this step vital.

Technician B emphasizes the need to evacuate the system any time it is opened for repairs. This is also accurate because opening the system can allow air and moisture to enter, contaminating the refrigerant circuit. To ensure that the system operates effectively after repairs, it is standard practice to perform an evacuation to create a vacuum, thereby ensuring that all contaminants are removed.

As both statements reflect important truths about the evacuation process and its necessity in maintaining a healthy air conditioning system, the correct answer recognizes that both technicians are correct in their assessments.