On systems using R-12, a sight glass is typically found with which component?

In systems using R-12 refrigerant, the sight glass is typically found in conjunction with the receiver/dryer. The role of the sight glass is to provide a visual indication of the refrigerant's state within the system, specifically showing whether the refrigerant is in liquid, vapor, or a mixture of both forms.

The receiver/dryer is a component that collects the refrigerant from the condenser and separates the liquid refrigerant from vapor, ensuring that only liquid refrigerant enters the expansion device (typically a thermal expansion valve). The sight glass allows technicians to monitor the system's condition, checking for issues such as being undercharged or overcharged, which can lead to performance problems.

While a thermal expansion valve is a critical component that regulates the flow of refrigerant into the evaporator, it does not usually incorporate a sight glass for monitoring refrigerant conditions. The sight glass is primarily associated with the receiver/dryer, where it can best help in assessing the refrigerant's state and health within the system. Therefore, it is crucial to associate the sight glass with the receiver/dryer for accurate diagnosis and troubleshooting in R-12 systems.