_______________________ should be used to purge air conditioning systems tubing while brazing.

Nitrogen is used to purge air conditioning system tubing while brazing because it serves several important functions. When nitrogen is introduced into the tubing, it helps to prevent oxidative reactions that can occur at high temperatures during the brazing process. This oxidation can lead to the formation of scale or oxides on the interior surfaces of the tubing, which can negatively impact the efficiency and longevity of the system.

Additionally, purging with nitrogen helps to remove any moisture or air that may be present within the system. Moisture can cause serious problems in refrigeration systems, leading to corrosion and reduced performance. Nitrogen is inert, meaning it won’t react with the materials in the system, making it the ideal choice for maintaining the integrity of the refrigerant lines during the brazing process.

Using a regulator with nitrogen ensures that the flow is controlled, allowing for effective purging without introducing excess pressure that could damage the system or create safety hazards. This method supports maintaining a clean environment inside the tubing, which is critical for the proper functioning of the air conditioning system.

The other options, such as air, carbon dioxide, and oxygen, are not appropriate for this purpose because they can introduce contaminants or create reactions that harm the integrity of the refrigeration components.