Where would a sight glass normally be located in a refrigerant system?

• A. In the liquid line, before the metering device
• B. In the suction line
• C. In the discharge line after the condenser
• D. In the oil line

Answer: (A)

You check the liquid line with a sight glass. After the condenser the refrigerant should be a high‑pressure liquid, so placing a sight glass in the liquid line before the metering device lets you visually verify that liquid is reaching the expansion device and, if the sight glass has a moisture indicator, whether the liquid is free of moisture. This position is chosen because it provides a direct view of the refrigerant state just before throttling, which is essential for confirming proper charge and subcooling. If the sight glass shows clear liquid with no bubbles (and the moisture indicator is safe), the system is typically in good shape. If you see bubbles or a moisture Color change, it suggests undercharge, inadequate subcooling, or moisture contamination, signaling a need to check charge, condensation, or contamination. Placing a sight glass in the suction line would show vapor, not useful for confirming liquid charge; in the discharge line you’d see hot gas; in the oil line there isn’t meaningful refrigerant state to observe.