Why is a refrigerant gauge called a compound gauge?

• A. It reads humidity
• B. It reads temperature
• C. It reads positive pressure and vacuum
• D. It reads only pressure

Answer: (C)

A refrigerant gauge is called a compound gauge because it can display both positive pressure (above atmospheric pressure) and vacuum (below atmospheric pressure) on one instrument. In refrigeration work, you often need to monitor pressure while charging refrigerant, and you may also evacuate the system to remove air and moisture. Having a single gauge that shows how high the pressure is and how deep the vacuum is lets you track both directions relative to atmospheric pressure without swapping instruments. It’s not about humidity or temperature, which require different tools, and it’s not just a pressure-reading device, since it also shows vacuum.