When pressurizing a refrigerant system with nitrogen, what rule should you always follow?

Charging a refrigerant system with nitrogen should always be done with a pressure regulator to control the pressure accurately and safely. This is important because nitrogen, when compressed, can create very high pressures that could potentially damage the system or lead to dangerous situations if not regulated.

Using a pressure regulator allows for a consistent and manageable flow of nitrogen into the system, preventing spikes that could exceed the system's rated pressure. Over-pressurizing can cause seals to fail or components to rupture, leading to costly repairs and safety hazards.

In contrast, charging nitrogen as a liquid is not advisable for pressurizing systems since nitrogen behaves differently when it is in liquid form compared to gas and could lead to uneven pressure distribution. Pressurizing to above 1000 pounds is excessive and typically unnecessary, as most systems are designed to operate within much lower pressure ranges. Lastly, while nitrogen can be used for troubleshooting and leak detection, it should not be used inside the refrigerant system as a permanent refrigerant; thus, the option suggesting never to use it inside the system aligns with proper safety practices.

Hence, the rule of always using a pressure regulator when charging a refrigerant system with nitrogen is critical for maintaining control and safety during the process.