When charging a system, the refrigerant cylinder pressure may drop too low for further charging. Which of the following methods should not be used to increase the pressure?

• A. Heat the cylinder with a heat lamp.
• B. Heat the cylinder by wrapping it in a specially built electric heater.
• C. Heat the cylinder by immersing it in a tub of warm water.
• D. Heat the cylinder with a torch.

Answer: (D)

Raising the cylinder’s temperature to increase pressure must be done with controlled, indirect heating. An open flame is not safe because it can heat the metal unevenly and rapidly, risking overpressurizing the cylinder, damaging the valve, or causing a rupture. The flame also creates a serious ignition hazard if refrigerant oil or vapors are present. In contrast, methods like a heat lamp, an electric heater wrapped around the cylinder, or immersion in warm water provide gradual, uniform heating, allowing the pressure to rise safely as the contents warm. If pressure still won’t rise or if anything seems abnormal, follow proper procedures rather than attempting further charging.