To safely increase the pressure in a refrigerant cylinder while charging the system, what should a technician do?

To safely increase the pressure in a refrigerant cylinder while charging the system, running warm water over the cylinder is the most effective and safest method. This approach gently raises the temperature of the refrigerant inside the cylinder, leading to an increase in pressure. When the refrigerant is warmer, it becomes more vaporous and can be more easily dispensed into the system.

The use of warm water is controlled and minimizes the risk of overheating or causing damage to the cylinder. It also allows the technician to maintain a close watch on the temperature increase, ensuring that the pressure does not exceed safe operating limits.

Other methods, like using a heat gun or leaving the cylinder in direct sunlight, can lead to uneven heating or excessive temperatures that might compromise the integrity of the cylinder or the safety of handling it. Moreover, placing the cylinder in a freezer would decrease the internal pressure, making it more difficult to extract refrigerant when needed. Therefore, running warm water is the preferred and safest method for managing cylinder pressure.