References to the pressure/temperature chart for determining the type of refrigerant are only valid if which parameter is known?

The correct answer is that the parameter known must be temperature. A pressure/temperature chart is essential for identifying the refrigerant because every refrigerant has a specific pressure associated with a certain temperature. When the temperature is known, you can accurately locate the corresponding pressure on the chart, which then allows you to identify the type of refrigerant in use.

Understanding the relationship between pressure and temperature is critical in refrigeration. As refrigerants change state (from liquid to gas and vice versa), their pressure and temperature will vary in predictable ways. Without knowing the temperature, it would be impossible to accurately determine what the corresponding pressure is, making identification of the refrigerant indeterminate.

On the other hand, pressure by itself does not provide a complete picture without knowing the temperature context. Temperature is the key factor that ties the two together and makes it possible to effectively use the chart for accurate analysis.