Final answer:
A bubbling sight glass would indicate a restriction in the liquid line of a refrigeration system. Other potential symptoms of a restriction include high pressure in the liquid line. So option (A) is correct.
Step-by-step explanation:
What would indicate a restriction (such as dirt or scale) in the liquid line of a refrigeration system? One common symptom is a bubbling sight glass. A sight glass is a viewing window on the liquid line that allows a technician to observe the flow of refrigerant. Bubbling can occur when the refrigerant is not able to flow freely due to a restriction, causing it to flash or vaporize prematurely. This could be due to a blockage from debris like dirt or scale. The key is that a steady stream of refrigerant should be visible; any form of inconsistency such as bubbling or gurgling indicates a problem. Alternately, high pressure in the liquid line could also be a result of a restriction, as the compressor works harder to move refrigerant through the obstructed line.