What color is the sight glass on a refrigerant system if moisture is present?

• A. Blue
• B. Green
• C. Red
• D. Yellow

Answer: (D)

Moisture in a refrigerant system shows up as a yellow color in the sight glass. The sight glass includes a moisture-sensitive indicator or desiccant inside, which changes color when water content rises above a certain level. When moisture is present, the indicator turns yellow, signaling that the refrigerant is not dry and the system should be evacuated and dried before charging. In many systems, a dry condition is shown by a green or blue appearance, so yellow specifically points to moisture.