Final answer:
In refrigeration system repairs using nitrogen, a regulator is essential for controlling the nitrogen flow and pressure safely.
Step-by-step explanation:
When repairing a sealed refrigeration system and using nitrogen, the nitrogen tank should always be equipped with a regulator. A regulator is essential for maintaining the proper flow and pressure of the nitrogen as it enters the refrigeration system. This Controlled pressure is crucial for the safety and effectiveness of the repair process. Other options such as a float sensor, red top, and hand valve provide different functions and are not primarily used for controlling gas pressure from a tank. Therefore, a regulator is always necessary when using nitrogen in such repairs. It is particularly important when dealing with dangerous gases or high-pressure situations.