What is a key procedure to follow when soldering?

Applying flux to the tubing rather than the fitting is important because flux serves as a cleaning and bonding agent that helps to prevent oxidation during the heating process. When soldering, it is crucial for the surfaces of the metal components to be free of impurities to ensure a strong bond. By applying flux to the tubing, it ensures that the surfaces of the tubing are adequately prepared for soldering, leading to better adhesion of the solder. This practice promotes a cleaner joint and enhances the overall strength and reliability of the solder connection.

In contrast, the other options do not follow best practices for effective soldering. Directly applying heat to the solder rather than the joint can prevent proper melting and adhesion. Using cold solder does not provide the necessary bonding strength and can result in weak connections. Additionally, cooling the joint before cleaning might allow oxidation to form, which would compromise the integrity of the solder joint. Thus, the correct application of flux is crucial in achieving successful and durable solder connections.