Final answer:
A visual indication of saturation in a liquid line filter drier is typically a change in color of a moisture-sensitive indicator. Not all filter driers have such indicators, and other signs include temperature or pressure differences.
Step-by-step explanation:
A visual indication that a liquid line filter drier is saturated and needs to be replaced is often provided by a sight glass or a color indicator embedded in the unit. When a liquid line filter drier—an essential component in refrigeration and air conditioning systems—becomes saturated with moisture or contaminants, the color indicator typically changes color. It's important to note, however, that not all filter driers have such visual indicators, and other signs of saturation include a temperature drop across the drier, or pressure differences observed before and after the drier.
In the case of moisture-sensitive color indicators, they commonly turn from a standard color like green to yellow, pink, or another color depending on the indicator's design. Implementing dyes like fluorescent green-dyed antifreeze, as seen when inspecting a car's radiator header tank, might indicate the presence of moisture; however, such additives are more common in automotive cooling systems than in filter drier indicators.